Section 1 Fungal Growth

#### **Chapter 1**

## Abiotic and Biotic Factors: Effecting the Growth of Keratinophilic Fungi

*Manish Mathur and Neha Mathur*

#### **Abstract**

Fungi portray an important role in decomposition of keratin, as their activity is tough to measure. According to an estimation, a quantity of cellulose is synthesized by primary producers over photosynthesis and then reinstated to the atmosphere as carbon dioxide and through the activity of fungi, which decompose the complex and inflexible polymer. Without this activity, the world would soon be submerged by plant residues, and this would probably exclude most living organisms from their natural habitat. This chapter deals with several abiotic and biotic factors, which effect the growth of keratinophilic fungus and the substrates, which can serve as potential growth promoters for them.

**Keywords:** keratinophilic fungi, growth factors, fungus substrate

#### **1. Introduction**

The degradation is associated to the aptitude of the organism to develop on a substrate. The capacity of the growth depends upon the enzymes secreted by the microbe and conditions such as PH, protein content in the substrate, temperature, moisture, etc. The native feather keratin was degraded by species of *Aphanoascus fulvescens* and *Chrysosporium articulatum*, which are separated from soil. Recognition of strain was done by phenotypical qualities and nucleotide sequencing of protein. The ultimate deficit of substrate in comparison to the strain was recorded for *Aphanoascus fulvescens* and deficit of substrate for the *Aphanoascus fulvescens (*71.08%). Keratin is high in protein and abundant in nitrogen and sulfur [1–3]. Keratins have high mechanical and chemical resistance. Numerous disulfide bonds (S–S) are liable for the resistance. Except a few months, only keratinolytic microorganisms can grow and degrade native keratin including some bacteria of the genera *Bacillus, Vibrio, Serratia* ([4], actinomycetes [5]). The genus *Bacillus* [6], representative geophilic dermatophytes are associated with the fungi known as *Chrysosporia*, name taken from the genus *Chrysosporium* [7]. The development of fungi is backed by a humus, neutral or a little alkaline pH reaction, fruitfulness in CaCO3 [8]. The *Chrysosporim* belongs to this group, specialized in the growth of keratin, e.g., feathers, hairs [9]. Although it is considered safe in certain stages but can be converted into pathogenic form under certain conditions. Kushwaha [9] reported that genus *Chrysosporium* is effective in disorienting keratin; however, keratin degradation varies in the species. Some microbes grow on keratinous materials including bacteria, biodegradation has been exhibited by *Bacillus*, particularly *Bacillus licheniformis* [10]

and *Bacillus subtilis* [11], and *Chryseobacterium*. Actinomycetes from *Streptomyces* genus produce keratinases [12, 13]. The most common keratinolytic fungi are *Aspergillus*, *Penicillium* [14], *Fusarium* [15].

#### **2. Growth factors in keratinophilic fungi**

To-Ka-Va hair baiting technique [16] was used in the experiments. Several workers projected that saprophytic phase of dermatophytic fungi in the soil are global [17, 18]. Dispersal of pathogenic fungi [17, 19–22] specifies soil turns as pool meant for primary contamination may be for some pathogenic fungi. Potentially it is pathogenic to wild animals and acts as the resource of secondary infection to man and pets [23–26]. Besides soil, birds' nests and feathers [27–35], hairs [25, 36], water [37], plant debris [38], and dung [39] are the different ecological places for growth of capable dermatophytic fungi.

Fungi produce enzymes potent of degrading keratinized forms known as keratinophyles. Pathogenic strains find a suitable host in favorable environmental and physiological conditions and produce the symptoms known as "ringworm diseases" by growing on human dermis.

#### **2.1 Climatic factors**

#### *2.1.1 Temperature*

Keratinophilic fungi are mesophilic while a few have grown at 37°C such as *C. tropicum, Chrysosporium keratinophilum, C. queenslandicum*, etc. Nevertheless, geophilic dermatophytes grow best at 25–30°C. In 1970, Pugh and Evans mentioned span of 25–27°C in the keratinophilic fungi, which do not grow more than at 40°C.

The broadly recognized view about mesospheric in nature has been disquieted by the results of Battelli et al. [40], about the existence of *Microsporuzri pypseiim, Trichophyton ajelloi, T. terrestre* in alpine mountain. Pugh and Allsopp [41] stated a recurring existence of *Chrysosporium pannorum* and *Mortierella* spp. with exceptional incidence of *Trichophyton terrestre* and *Chrysosporium* sp. Some varieties are thermotolerant, and recently, it was shown that they can adapt to adverse temperatures for survival [41].

#### *2.1.2 Light*

It was known that the UV light is fungicidal, which creates about a reserve of spore sprouting leading to a hypha. Excellence of illumination on spore germination has entirely been analyzed by Buchnicek [42].

First shown by Berde [43], the growth reticence of dermatophytes is via means of lamp. Fungicidal effect in *Candida albicans* differed with the strength of light sensitizer and light intensity as was observed by Dickey [44]. There is no effect on illumination of spore suspension of *T. mentagrophytes* without photosensitization [44]. The red or blue light when applied separately prevents the growth greater than visible light. The quantity of inhibitions by both color lights utilized individually is more than the reserve by their mixture.

#### *2.1.3 Seasonal variations*

Season is quite anticipated with respect to dermatophytic flora of the soil, which has climatic differences resulting in change of temperature. *Keratinomyces ajelloi,* 

*Abiotic and Biotic Factors: Effecting the Growth of Keratinophilic Fungi DOI: http://dx.doi.org/10.5772/intechopen.103716*

*Trichophyton Terrestre, and Microsporum gypseum* were found in soil samples during April and in August.

#### *2.1.4 Soil pH*

Effects of pH on microbial life are explored extensively. Bohme and Ziegler [45] observed about soil pH as verified by Pugh [32]. Ziegler [46] observed the degradation of keratin over a wide range. Findings uncovered the optimum pH for amylase 7–2, alkyl phosphates 8–7, lipids 6–8, proteinase 5.4–6.9. Ectoenzymes are shown dormant at pH below 4.5, and the enzymatic catabolism of keratinophyles occurs at pH 6.9. Ziegler [46] further confirmed that the most luxuriant growth and highest frequency of keratinophilic fungi were seen in soils with pH 6.9.

#### *2.1.5 Carbon*

Decomposition of carbon can be done by keratinophilic fungi but there is not enough information regarding carbonate impacting the delivery in soils. Chmel et al. [47] described favored incidence of *M. qypseum* in carbonate field soil, an alliance of *K. ajelloi* with soils and a predilection of T. *terrestre* in alluvial soils. It was studied that a plenty of keratinophilic fungi in carbonate field and chernozemic soils have greater humus substance in comparison to gray podzolic soils. Keratinophyles can decompose extremely compound carbon complexes in many culture media, a simple carbon source can be used and not influence their qualitative spreading but the findings on their quantitative dispersal may disclose fascinating truths.

#### *2.1.6 Nitrogen*

Keratinolytic fungi can decompose keratin, which is a rich source of nitrogen. Rate of keratinolysis has been reported by Ziegler [46] at pH 6–9 supporting the earlier finding.

Growth of *Microsporum gypseum* is fine revealed by the experiments utilizing optically dissimilar forms of cystine, quite large amounts in the scleroprotein [48]. Carbon and nitrogen application was perceived when surplus sulfur was secreted in the medium and became oxidized. Oxidation of sulfur in the extracellular medium makes use of L-cystine, which was showing a slow form. The way of consumption of L- and D-L-cystine was the same. The nitrogen-containing substances of keratin differ from one another and in opportunity would impact colonization of the last.

#### *2.1.7 Sulfur*

Kunert [49, 50] calculated that the inorganic and organic sulfur resources for the development of the fungus *M. gypseum.*, sulfite, disulfide, peroxodisulfate dithionate, and sodium sulfate were the best hints of inorganic sulfur. Inorganic sources sulfide produced a primary inhibition of the fungal growth supportive to a previous report that mineral water comprising H2S is repressing for the growth of dermatophytes. Amino acids such as cystine, cysteine, glutathione, S-sulfocysteine, lanthioneine, taurine, and serine-sulfate are the leading organic sulfur sources of the fungus.

#### *2.1.8 Moisture content*

An enzymatic reaction takes place in aqueous solution in the cell cytoplasm and is vital to life. The systems of germination, growth, and reproduction are energetic

associated to the substrate moisture content. Pugh and Evans described a better percentage of spore growing in *Arthroderma uncinatum* and *Ctenomyces serratus* at 90–100% RH. It was also stated that an plenty of keratinophyles in birds' nest with moisture usually showed a greater occurrence of keratinophilic fungi in bird nests with 15–20% water content [51].

#### *2.1.9 Humus*

High humus content in soils invites M. *gypseum* and *T. terrestre* in soils as revealed by Chmel *et al.* [47]. Whereas distribution of K. *ajelloi* and *C. keratinophilum* is regardless of soil humus. Soils made up of fragmented lava with little organic matter in the Galapagos Islands revealed by Ajello and Padhye [52] reported the occurrence of *A. quadrifidum, C. indicum*, C. *keratinophilum, C. tropicum,* and *Ctenomyces serratus*. A higher number of keratinophilic fungi were described in soils with exceptional humus value. In all levels of soil profile extreme in the region with high humus content, there exist *M. gypseum and T. georgii,* while *T. oanbreuseqhemii* and its flawless state *A. gertleri* were primarily found in soils with low humus value.

#### *2.1.10 Fatty acids and oils*

In 1899, Clarke antifungal estates of fatty acids were known to scientific world. The anti-dermatophytic properties were discussed by Rigler and Greathouse in 1940, which was later validated by Das and Banerjee [53].

Hajini et al. [54] studied unsaturated fatty acids, hair oils, and various natural fatty acids for their anti-dermatophytic properties. Reticence of growth of *T. rubrum* and associated dermatophytes was at 0.1% strength of mustard oil, oleic, linoleic. Linolenic, and aracliidionic acids while coconut oil, castor oil, till oil, Bryl cream, vaseline hair tonic, palmitic acid, and stearic acid did not prevent the growth even at 10% strength.

#### *2.1.11 Salts*

In coastal soils, various keratinophilic fungi can survive. *A. curreii* occur although the rate of availability of keratin must be small. Varieties of hares, rabbits, and birds exhibited *A. curreyi* and *C tenomices serratus*. Padhye *et al.* [55] isolated *Clirysosporium tropicum* and *Microsporum* gypseum from long immersed marine soils in Bombay. *C. indicum* and *Cteiiomyces sermons* and inaccessible to somewhat irregularly. The fungi remain to be revealed, for no such fungi have been found from coastal Mediterranean soils, which have salinity. A repressive sodium chloride impact on the growth has been stated of dermatophytes. Growth was reserved by NaCl in *Microsporum, Epidermophyton, Trichophyton,* etc*.*

#### **2.2 Biotic factors**

Biotic component influences the occurrence of keratinophilic fungi as the main causal factor in spread and persistence of ringworm diseases produced by dermatophytes up to a great extent. Biotic component influences the occurrence of fungi in birds and animals.

#### *2.2.1 Birds*

Pugh [56] displayed the existence of keratinophilic fungi on the experimental birds although validated them on birds in Australia. An association exists in the

keratinophilic fungi and birds of correct order, *e.g., A. curreyi* and *Turdus* [31]; *C. serratus* and representatives of Galliforme, particularly partridges and chickens. Regularly conveyed from most of the bird forms [56], in *Chrysosporium* spp. Commonly found species are *C. k eratinophilum, Keratinomyces ajelloi,* and *T. terreste*. There was significant habitation for the cleistrocarpic stage of *C. serraius.*

#### *2.2.2 Animals*

The role of wild animals as carrier of these diseases has been documented earlier in literature.

Occurrence of *Tinea capitis* was in newborns who obtained disease from stray kittens. Incidence of scalp abrasions in an 8-year-old boy and a 3-year-old Yorkshire was seen as well as subsequent isolation of *Microctenopoma nanum* from soil. Soil acts as a group for dermatophytes [57].

#### **3. Fungal growth on feathers**

Keratin makes feather obstinate to common proteases such as trypsin, pepsin, papain, slowing its degradation process. Each bird has up to 125 gm of feather and approx. 400 million chickens processed universally the daily accumulation of which reaches 5 million tons [58, 59]. According to Lin *et al.* [60], the waste disposal is a global issue foremost to pollution of both air and water resources. Keratinasetreated feather is considered as a viable source of dietary protein in food and feed, as it has high nutritive value. Keratinases are potential market as proteases. Microorganisms are described to produce keratinase as *Doratomyces microsporus, Alternaria radicina, Trichurus spiralis, Aspergillus sp., Rhizomucor sp., Absidia sp,* etc., and *actinomycetes as Streptomycespactum*, *S. alvs*, *Streptomyces thermoviolaceus, Streptomyces fradiae, Thermoactinomyces candidus* etc.), and as bacterial species (*Fervidobacterium islandicum, Pseudomonas aeruginosa, Microbacterium sp*., and *Bacillus* including *Bacilluslicheni formis* and *B. pumilus*) [61]. Feather is insoluble fibrous protein and highly resistant [62] to enzymatic digestion [63]. Though, fungi often colonize on various keratinous substrates, degrade them and enhance the minerals in soil [64].

Hydrolytic enzymes are synthesized by filamentous fungi. Various species are used to produce industrially important enzymes as distinct proteases, carbohydrates, and lipases. It is the key enzymes in fungal incursion of skin found in dermatophytes as *Trichophyton* [65]. *Candida* also contributes to skin infections. Enzymes are found in *Streptomyces* [66] and *Bacillus* spp. [60]. Novel and Nickerson [67] examined bacteria, actinomycetes, and fungi for keratinolytic activity and found *Streptomyces* as most active in the decomposition of sheep wool. Keratin hydrolysis was the most active in *Verticillium tenuipes, Trichophyton equinum,* and *T. mentagrophytes* in peacock feathers*. T. mentagrophytes, T. verrucosum,* and *Keratinomyces ajelloi* degraded hair, whereas only *T. gallinae* degraded chicken feathers.

#### **4. Fungal growth on hair**

Keratin, the fibrous protein, is a codified part of hair, wool, and related structures, which differ from other proteins in their high cystine content.

Five keratinophilic fungi, i.e., *Chrysosporium indicum, Geotrichum candidum, Gymnoascoideus petalosporus, Scopulariopsis brevicaulis,* and *Talaromyces* 

#### *Fungal Reproduction and Growth*

*trachyspermus,* which grow on human hair in stationary culture, have been examined. Hair was studied on criteria of cysteine, cystine, inorganic sulfate, thiosulfate, total protein, keratinase, and change in alkalinity. *Gymnoascoideus petalosporus* showed degradation to remaining isolates when grown on human scalp hair as the sole resource of nutrients *in vitro.*

Kunert [68, 69] described a release of cystine, cysteine, and sulfate in the culture filtrate of *Microsporum gypseum* growing on hair. Ruffin et al. [70] discovered the S-sulfo cysteine in culture fluid and established the role of sulfitolysis during keratin degradation by *Keratinomyces ajelloi.* Stahl et al. [71], Chesters and Mathison [72], and Ziegler & Bohme [73] could not detect cysteine in filtrates of the dermatophytes studied. Weary et al. [63] recorded the production of 21 pg./ml and 38 pg./ ml of cysteine by two strains of *Trichophyton rubrum.*

#### **5. Fungal growth on leather**

Samples collected from different museums of feather and leather objects and deposited dusts were studied for the isolation of keratinopliilic and nonkeratinophilic fungi. Throughout the study, five species of *Chrysosporium*, four of *Aspergillus*, one of *Penicillium,* and two each of *Acremonium* and *Fusarium* were isolated.

Deterioration of objects of cultural value, in the conservation of cultural heritage, is a real problem. Microbial activity on museum objects, especially skin or leather, starts with a surface infection that eventually invades the full thickness of the skin. The most common molds belonging to the genera *Aspergillus* and *Penicillium* emerge as black and green surface discoloration. There are, however, other molds, although of rare incident compared with the above, causes degradation of skin objects [74–76].

From different museums of Northern India, 24 keratinophilic and nonkeratinophilic fungi represented by five genera and 15 species were isolated. Strains of *C. keraiinophilum,* three of *C. tropicum,* two each of *C. evolceanui* and *C. indicum,* and one *Chrysosporium* sp. were found in museums. Some nonkeratinophilic fungi, i.e., three isolates of *Aspergillus flavus,* three of *A. niger,* one each of *A. sulphureus* and *A. luchuensis,* two species of *Penicillium, i.e., P. ciirinum, P. chrysogenum,* and two species of both of *Fusarium* and *Acremonium* were found and called as non-keratinophilic [77]. These were involved in the degradation of feather and leather objects.

Keratinophilic and non-keratinophilic fungi arise in regions where they can find dissimilar types of keratinaceous substrates. The existence of the fungi was connected with numbers of people inhabiting [47]. English [78] found 31 saprophytic fungi capable of inhabiting keratin along with non-keratinophilic fungi on keratinic substrate witnessed by Nigam and Kushwaha [77]. *Aspergillus* and *Penicillium* colonized keratinous substrates, and pathogenic behavior was revealed by Kishimoto and Baker [79]. The capacity of these fungi to colonize keratinous substrates was confirmed by Carmichael [80]. Some saprophytes are involved in microbial deterioration of leather [81, 82].

Keratinophilic fungi were commonly found on birds and animals and also isolated in the Antarctic [74]. Isolation of *Chrysosporium* spp. is supported by other work, and it was frequently isolated [55, 83–88]. The presence of *Chrysosporium* and related keratinophilic fungi was reported from museum objects, their surroundings, or their deposited dusts.

In 2006, several valued leather objects were found during archeological excavation of Ghalee-Kooh-i Ghaen (historic stronghold from the Seljuk

#### *Abiotic and Biotic Factors: Effecting the Growth of Keratinophilic Fungi DOI: http://dx.doi.org/10.5772/intechopen.103716*

period, 11th–13th centuries) in the South Khorasan province of Iran. When examined after 5 years, there were red stains on the fragments of a shoe with poor strength and powdery surface like red rot decay. Since red rot is more common in manmade leathers from the mid-nineteenth century as clarified by the structural features and degradation factors responsible for red stains on the shoe.

As leather production is an ancient industrial activity [89], historical and archeological leathers represent an important part of any society's cultural materials. *Ghalee-Kooh-i Ghaen is* a fortified castle from the Seljuk period (11th–13th centuries) located 3.4 km from Ghaen city in the South Khora-san province of Iran [90]. It was destroyed in 1066 A.D. by an intensive earthquake in the Ghaen area [91]. Later, Hossein Ghaeni rebuilt the castle in the late eleventh century to use as headquarters in the southern part of Khorasan known as Ghohestan [92]. The castle was registered as no. 4803 in the list of Iranian national monuments due to its historical and archeological value in 2002.

Several leather bottles, shoes, a fur, and some pieces of leather were found in the archeological investigation. Studies of the leather bottles indicated goat skin treated with lime depilation, vegetable tanning, and animal fats as lubricant for leather making. After excavation, the leathers were stored in inappropriate conditions at the base of the cultural heritage organization of South Khorasan province without any preventive measures. During the time of storage, there was no information about the environmental condition of the leathers within their archeological context in 2011 one of the excavated shoes was examined. Red rot is more common in manufactured leathers from the **mid-nineteenth** century, but the decomposition pattern may be found in more ancient leathers as well [93]. Therefore, this leather shoe was studied to better understand the deterioration mechanism prior to any interceptive activities.

Previous investigations on the structural features and degradation of leather and parchment artifacts have revealed important information, which is of value to our study [94, 95]. Sulfuric acid is regarded as main deterioration factor of red rot [96], possibly originating from environmental pollution or the materials used in the leather-making process [97]. Additionally, the production of acid from vegetable tannins, especially condensed and disintegration of the collagen-tannin complex, may result in red rot [96]. Many methods are available for identifying the decay, such as assessment of esthetic properties, pH and evaluation of the physical and mechanical characteristics of the object [96–98]. Red rot probably occurs in leathers with pH under 2.8. However, the degree of degradation cannot be determined just by pH measurement [98]. Moreover, biodeterioration is another important factor altering the artistic and useful properties of leather [99]. Fungi species attach to materials such as paper, textile, wood, paints, leather, etc., and produce characteristic signs that can be used for identification [100]. Leather composed of collagen, i.e., fibrous protein, provides a source for the evolution of proteolytic fungi. Some species of Aspergillus and *Penicillium* have been identified as the most common species related to leather and parchment molds [101]. There are also other rare molds responsible for biodeterioration of proteinous materials. Ebrahimi et al. [100] observed the activity of *Aspergillus* spp., *Penicillium* spp., *Chrysosporium* spp., *Madurella* spp., *Trichophyton* spp., and *Zygomycota* on the leather artifacts in Shahrekord Museum, Iran. Abdel-Maksoud [102] identified Penicillium spp., *Aspergillus* spp., and *Fusarium* sp. as the most profuse fungi found on a leather book binding of a Quranic manuscript from the nineteenth century. Nigam et al. [103] attributed degradation of leather and feather objects in Indian museums to keratinophilic and non-keratinophilic fungi.

#### **6. Fungal growth on wool**

Common method of isolating dermatophytes of so-called "keratinophilic" fungi is by baiting with hair [104, 105]. Little is known of the relationship of these nondermatophytic fungi to the decomposition and utilization of keratinous substrates, although previous studies [78] have indicated that role in the breakdown of keratinous tissue may be significant.

Fungal succession on woolen baits was studied and was found that the initial colonizers on woolen baits are non-keratinophilic fungi, while the late colonizers are keratinophilic fungi comprising six phases during fungal succession. The successional tendencies obtained during degradation of wool in samples collected from plain and hilly areas, apart from for the prevailing colonization in the last phase, composed of *chrysosporium tropicum* for the plain, but *Miorosporum* gypseum and *M. fulvum* for the hilly area.

Various workers [68, 69, 75, 76, 106–109] studied degradation of keratinous material, but none of them reported the involvement of other soil microbes in the decomposition of keratin. On succession of fungi on keratinous material [104], little but adequate information on fungal succession on woolen baits is still lacking.

The archeological textiles have a unique position in archaeology, textiles probably contain much archeological information, even more than ceramics. During the Bronze Age (1700–500 BCE), the trade of wool textiles was complex, widespread, significant, and possibly important as the metals [110]. Foundation of economic and political development in the late Middle Ages (c. CE 1100–1500) [111] was Trans-European trade of these materials.

#### **7. Conclusions**

The keratinophilic fungi can cause superficial mycosis both in humans and animals. They include a variety of taxonomic groups of filamentous fungi, one of them being the dermatophytes fungi. The keratinophilic fungi can produce a specific enzyme named keratinase that is responsible for keratin degradation. Keratinases can be serine proteases or metalloproteases [86]. The keratinophilic fungi could use keratin from keratinized materials (superficial layers of the skin, hair shaft and nails in humans and claws, horns, wool in animals) as the unique source of carbon and nitrogen. Keratin is found predominantly in feathers, hair, nails, horns, hooves, furs, claws, bird beaks, skin and consists of two types of keratin: α (alpha) and β (beta)-keratin; α keratin (soft) is usually found in hair, wool, horns, nails, claws, and hooves, whereas β keratin (harder) is found in bird feathers, beaks, and claws. Understanding of abiotic and biotic factors and role of different substrates for the growth of these fungi can help researchers to study their growth pattern and conduct their studies for better management of these fungi.

#### **Conflict of interest**

The authors declare no conflict of interest.

*Abiotic and Biotic Factors: Effecting the Growth of Keratinophilic Fungi DOI: http://dx.doi.org/10.5772/intechopen.103716*

#### **Author details**

Manish Mathur1 and Neha Mathur2 \*

1 Amity University, Lucknow, Uttar Pradesh, India

2 Amity Institute of Pharmacy, Lucknow, Amity University, Noida, Uttar Pradesh, India

\*Address all correspondence to: nmathur1@amity.edu; neha07.mathur@gmail.com

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 2**

## Fungal Growth and Mycotoxins Production: Types, Toxicities, Control Strategies, and Detoxification

*Chinaza Godswill Awuchi, Erick Nyakundi Ondari, Ifie Josiah Eseoghene, Hannington Twinomuhwezi, Ikechukwu Otuosorochi Amagwula and Sonia Morya*

#### **Abstract**

Fungal growth and the production of mycotoxins are influenced by several factors. Environmental conditions such as temperature, water activity, and humidity affect mycotoxin production and fungal growth. Other factors such as pH, fungal strain, and substrate also play roles. Common mycotoxins include aflatoxins, fumonisins, trichothecenes, sterigmatocystin (STC), citrinin, ergot alkaloids, ochratoxins, zearalenones (ZEAs), patulin, deoxynivalenol (DON), Alternaria toxins, tremorgenic mycotoxins, fusarins, cyclochlorotine, sporidesmin, 3-nitropropionic acid, etc. These toxins cause many health conditions in animals and humans, including death. A comprehensive approach starting from the field before planting, continuing throughout the entire food chain is required to control mycotoxin contamination. Good practices, such as proper field practices before and after planting, good harvest practices and postharvest handling, and proper drying and storage measures, help reduce mycotoxin contamination. Several physical, biological, and chemical techniques have been applied to help reduce/eliminate mycotoxin contamination. Food processing also play slight role in mycotoxins removal.

**Keywords:** Fungal growth, Mycotoxin production, Mycotoxin toxicities, Mycotoxin control and detoxification measures, Factors affecting mycotoxins production

#### **1. Introduction**

Fungi are members of the group of eukaryotic organisms that mainly include molds and yeasts. Where conditions are favorable, fungi produce mycotoxins, which are naturally occurring toxic secondary metabolites produced by some fungi, mostly molds, which grow on several crops and foods such as nuts, apples, grains, coffee, fruits, spices, etc., before and after harvest. These filamentous fungi are among the microorganisms that metabolize many organic substances such as sugars, lipids, proteins, etc. Fungi are naturally abundant and ubiquitous and have the capability to attack crops in field, after harvest, and during storage, and can survive under several environmental conditions including humidity, temperature,

pH, water activity (aw), etc. [1, 2]. Fungi commonly invade the commodities consumed by animals and humans, and due to their growth on the commodities, they produce low molecular weight secondary metabolites called mycotoxins [3]. Mycotoxins have been recognized as emerging toxins of concern worldwide [4]. Although more than 100,000 fungal species are known, only few, such as species of *Aspergillus, Fusarium, Penicillium,* etc., are known to produce most of the mycotoxins that significantly affect agriculture, humans, and animals [5].

At present, at least 300 mycotoxins are known, with the widely varied fungal origin, function, structure, toxic potency, and biological effects, although only a few have established significant effects on agriculture, animals, and humans [6, 7]. Many of them have not been sufficiently studied. All mycotoxins identified have between four carbon and complex carbons, which is mainly a result of the different biosynthetic pathways involved in their production [3]. As the production of mycotoxin has not been reported to have any significant biological effect on the growth of fungi, they might play a role in defense mechanisms against several intruders such as insects, animals, nematodes, microorganisms, and even humans [8, 9]. Production of mycotoxins may play role in the maintenance of cell oxidative status at a level essential for the safety of fungi [10]. Several mycotoxins have numerous toxic effects on animals and humans; they pose a real health concern to the public, as they are widely spread in foods worldwide [11].

Mycotoxigenic and pathogenic fungi are common in almost all regions worldwide. They invade, colonize, and grow on many crops, producing mycotoxins under various conditions such as environmental conditions [1]. Several factors have effects on the growth of fungi and production of mycotoxin, and in general, contamination with mycotoxins occurs at various points in the food chain [1]. Fungi presence, however, does not automatically signifies subsequent mycotoxin production, as the conditions required for mycotoxins production are definitive and independent from the conditions that promote the growth of fungi [12, 13]. This chapter throws insight into fungal growth and consequent production of mycotoxins, including their types and toxicities. The chapter also provides methods and strategies for mycotoxins control and detoxification.

#### **2. Fungal growth conditions and mycotoxin formation**

Several factors influence fungal invasion, colonization, growth, and consequent production of mycotoxins [14]. The most significant conditions favorable for growth of fungi and production of mycotoxin include temperature and aw. The optimum temperature for production of mycotoxin by several molds range from 20 to 30°C. Generally, in the tropics and subtropics which are characterized by warm climate, aflatoxins B1, B2, G1, G2, M1, and M2 (AFB1, AFB2, AFG1, AFG2, AFM1, and AFM2 respectively) are of main concern, whereas fusariotoxins, e.g. trichothecenes occur mostly in regions with moderate climate [15, 16]. Additionally, stress factors, including mechanical damage, insect ingression, weed competition, high crop densities, poor fertilization, and drought, can weaken the natural defense mechanism of plants and, as a result, promote fungal colonization, mycotoxin production, and formation of toxins. The optimum conditions for production vary along with temperature, substrate, humidity, and type of mycotoxin [17–19]. Interactions between temperatures and aw with respect to *F. Verticillioides* growth and mycotoxins production have been studied [17]. The study reported that at 0.995 aw, the optimal *F. verticillioides* growth rate ranged from 20 to 25°C, however, when the aw reduced to 0.98, the optimal temperature for growth shifted to 30–35°C. The conclusion was opposite for the production of mycotoxins. For example, the optimum aw and temperature for *Fungal Growth and Mycotoxins Production: Types, Toxicities, Control Strategies… DOI: http://dx.doi.org/10.5772/intechopen.100207*

the production of fumonisin B1 (FB1) were 0.98–0.995 and 20°C respectively [17]. This shows that the optimum conditions required for mycotoxins production differ from those required for their growth. **Figure 1** shows the minimum, optimum, and maximum required by some fungi for the production of mycotoxins.

The growth of Fungi is categorized into primary and secondary growths. In primary growth, organic compounds are required for the biomass synthesis and production of energy needed to drive chemical reactions to produce the primary metabolites that are essential for growth; secondary growth takes place after the phase of maintained growth and may, sometimes, lead to sporulation and secondary metabolites production [1]. The secondary metabolites, including mycotoxins, have no significant impacts on the fungal growth, but appear to be produced as a result of the excess accumulation of the precursors of primary metabolites, as a means to reduce their concentrations in the fungi [12]. As the fungi that produce mycotoxin and their targeted hosts are diverse in nature, it is difficult to define a single set of conditions which ultimately leads to mycotoxin production. However, in general, the main factors which affect the production of mycotoxins, include temperature, relative humidity, aw, substrate, fungal strain, and pH.

#### **2.1 Temperature, relative humidity, and water activity**

Environmental factors play significant roles in determining the occurrence of fungi; the fungal activities and colonization are predominantly determined by conditions such as temperature and humidity [21]. These factors influence the mycotoxigenic fungal prevalence, development, frequency, distribution, and survival, and their subsequent accumulation of toxin. Also, humidity and temperature affect plant growth, health, strength, and influence the mycotoxigenic fungal competitiveness. Due to differences in growth requirements and the environmental factors, fungal development and production of mycotoxin differ from one geographical region to another [22–24]. Before harvest, on the field, fungi *Fusarium* species mostly dominate since they are hygrophilic and require at least 90% relative

#### **Figure 1.**

*Minimum, optimum, and maximum range of temperatures (°C) for the production of mycotoxins (adapted from [20]).*

humidity (RH) to germinate/grow. Whereas after harvest, the hygrophilic fungi are not seen, as xerophylic and mesophilic fungi, such as *Penicillium spp.* and *Aspergillus spp.*, germinate and grow, leading to mycotoxins production at 80% or less RH and 80 to 90% RH, respectively [23]. In storage, if the surrounding environment's RH is more than the food's equilibrium RH, the food gains moisture and its aw increases [25]. Increased aw during storage increases the food vulnerability to fungal invasion, germination, growth, and production of mycotoxin. The major optimal factors for fungal growth and mycotoxin production are shown in **Table 1**.

For temperature requirement, most fungi are mesophilic and grow in range of temperature between 5 and 35°C, with optimal growth occurring around 25–30°C [1]. In addition, there are species of fungi called psychrophiles (tolerant to low temperatures) and thermophiles (can bare high temperatures). When there is shift in optimal temperature range (see **Table 1**), it may lead to a halt in growth [28]. The conditions that encourage the growth of fungi may not necessarily result in the production of mycotoxins. However, temperatures of 25–30°C, aw above 0.78, and RH of 88–95% favor fungal growth and production of mycotoxin [23, 25]. The most common mycotoxins, their toxicities, and fungi that produce them are shown in **Table 2**. Most of these mycotoxins are carcinogenic, genotoxic, mutagenic, immunotoxic, teratogenic, etc.

#### **2.2 Fungal strains**

There is variation in the toxicity of Fungal species and their mycotoxins production may usually depends on species, strains, and/or genera. The production of mycotoxin is influenced by strain stability, variation, and specificity [29]. Strains of the same species can have different optimum conditions required for growth and production of mycotoxins; also, strains of the same species can produce one or more different mycotoxins. For instance, while *Aspergillus flavus* can thrive within 15 to 44°C and produce aflatoxin B1 (AFB1), *Aspergillus carbonarius* thrives at 8 to 40°C and produce ochratoxin A (OTA) [23].

#### **2.3 pH**

The surrounding medium and its pH influence the development of fungi and production of mycotoxins. pH of the surrounding medium affects fungal growth either by direct or indirect actions on cell surfaces or on nutrient availability


#### **Table 1.** *Optimal conditions for fungal growth and mycotoxin production [26, 27].*


*Fungal Growth and Mycotoxins Production: Types, Toxicities, Control Strategies… DOI: http://dx.doi.org/10.5772/intechopen.100207*



**Table 2.** *Common mycotoxins, their producing fungi, and known toxicities [1, 2, 25].*

*Fungal Growth and Mycotoxins Production: Types, Toxicities, Control Strategies… DOI: http://dx.doi.org/10.5772/intechopen.100207*

respectively. Fungi can modulate the pH of the surrounding medium through secreting alkali or acids; species of *Aspergillus* and *Penicillium* can acidify the surrounding through citric and gluconic acids secretion [30]. The ability to control the pH provides fungi a better possibility of surviving in their host. In addition, the pH can have influence on the interactions of temperature and aw, as it affects metabolic processes, including morphogenesis and sporulation [31].

The pH can also affect the gene expression for biosynthesis, e.g. at pH 8, the genes responsible for production of ochratoxin A by *Penicillium verrucosum* are expressed [32]. Although the pH effect on the production of some mycotoxins has not been fully established for every type of mycotoxins, however acidic conditions are known to promote germination and production of mycotoxin. Production of aflatoxins requires pH 4.0 and the pH has inverse relationship with the level of synthesis [12]. In the same way, OTA levels are higher when *Aspergillus ochraceus* are at low pH [32]. Fumonisin B1 (FB1) is unstable in alkaline medium and requires pH 4.0–5.0 for synthesis; production of trichothecenes is initiated in acidic conditions [12].

#### **2.4 Substrate**

Mycotoxigenic fungi grow on several substrates, however, the major reason for their predominate on some foods has not been sufficiently established. The nutrients needed for the fungal growth, mostly nitrogen and carbon, are commonly found in foods, especially those rich in carbohydrates, molds are found in many foods [33]. Substrates that encourage the growth of fungi may not necessarily be support mycotoxin production, as conditions that promote the production of mycotoxins are usually different from those needed for fungal growth (see **Table 1** and **Figure 1**). Generally, mycotoxins production is greatly influenced by the interactions between many factors in substrate, such as temperature, aw, pH, and composition (e.g. simple sugars). The substrate's osmotic pressure affects the growth of fungi and the production of mycotoxin, and several studies reported that it can aid in evaluating fungal physiological responses, as well as can affect the secondary metabolites biosynthesis such as mycotoxins biosynthesis [34]. On the other hand, upon osmotic stress fungal species adjust their physiological responses to enhance their survival and adaptation [34].

Sugars have carbon and filamentous fungi have the natural ability to hydrolyse several sources of carbon to support growth and produce energy [35]. Consequently, in sugars presence, such as the presence of simple sugars, which readily breakdown, there is higher frequency of fungal growth. When complex sugars dominate, fungal growth is slower as the complex sugars need further digestion to yield simpler units of carbon that are readily absorbable. Simple sugars may contribute to the mycotoxins production. [36] reported that increase in the concentration of soluble sugars to 3 and 6 percent, especially maltose, glucose, and sucrose, promoted production of AFB1 in cell cultures. [37] also reported that more production of AFB1 by *Aspergillus flavus* resulted from an increase in the medium sugar levels.

#### **2.5 Effects of climate change on mycotoxins production**

Climate change has resulted in changes in most environmental conditions, including rise in global temperature which is expected to increase by 1.5–4.5°C by 2100 [38]. A rise in droughts, precipitation, flooding, and extreme weather conditions are expected [39]. Climate change and global warming affect food security greatly, including reduction in crop quality, reduction in yields, and increased food *Fungal Growth and Mycotoxins Production: Types, Toxicities, Control Strategies… DOI: http://dx.doi.org/10.5772/intechopen.100207*

safety challenges making some crops unsafe for human and animal consumption. Global change affects mycotoxin production, mainly by affecting the environmental conditions that influence their production [40].

Climate change affects different regions in various ways, with some regions having advantage whereas the opposite is the case for other regions [41]. The Mediterranean basin and Southern Europe most likely experience significant changes resulting in increase in mycotoxin prevalence, while the effects of climate change are anticipated to be positive in northern Europe [42]. As fungal growth, their germination, and production of mycotoxins are largely influenced by environmental conditions, especially the optimal conditions, temperature changes and change in humidity induced by climate change may several effects on production of mycotoxins. The mycotoxins usually produced at low temperature may not be produced at higher levels, whereas others predominant in tropical and sub-tropical regions, including aflatoxins, may be produced in temperate regions as a result of the expected rise in temperatures in these regions; for example, in Italy, in 2003 and 2004, hot and dry conditions resulted in the *Aspergillus flavus* colonization and aflatoxins production [43]. Different mycotoxins can be affected differently, usually based on the optimum conditions required for their production. Climate change also affects mycotoxins production indirectly via the increase of pest and insect populations, global spread, and attacks, early maturing and ripening of crops, decreased plant resilience, and change in host pathology upon the presence of CO2 in the atmosphere [42, 44].

#### **3. Mycotoxins prevention and control**

The production of mycotoxins has shown unavoidability and, as a result, many foods are being contaminated regularly. Mycotoxins greatly and widely vary and are produced by many fungi at various stages, on many crops, and consequently, a specific strategy for controlling all the mycotoxins has proven difficult with little or no success in decontaminating the affected foods or reducing all the mycotoxins to safe levels; most specific control strategies may only be effective in reducing the levels of specific types of mycotoxins. However, certain control measures can be employed to prevent or minimize their entrance, production, and occurrence in foods. Currently, no method has proven sufficient to totally control all mycotoxins. A successful strategy may adopt a combination of food safety system involving suitable quality measures at every production stage to reduce the frequency of mycotoxins occurrence in the final food products, which would include taking appropriate measures before, during, and after harvest. **Table 3** shows the overview of the action mechanisms of mycotoxins.

#### **3.1 Mycotoxins control using appropriate field practices**

Most fungi are phytopathogens that infect the crops in field, and their preharvest management is very important. In general, fungi that mostly predominate in field include *Alternaria spp., Cladosporium spp.,* and *Fusarium spp.* However, *Penicillium spp.* and *Aspergillus spp.* also occur in field at low levels and the contamination levels in general are usually higher anywhere climate conditions are favorable to the production of mycotoxin [45]. Whereas it is unlikely to totally prevent the production of mycotoxins in the field before harvest, it is of extreme importance to adhere to strategies which aim to reduce contamination to the barest possible minimum in preharvest. To choose and implement suitable strategies, a sufficient knowledge about the mycotoxigenic fungi, crops mostly affected, harvesting


#### **Table 3.**

*Mycotoxins action mechanisms [2].*

practices, and proper field management play important role [46]. Many factors such as delayed harvesting, poor soil fertility, heat, insect infestation, and drought contribute to the production of mycotoxins in the field [46, 47]. Appropriate practices in the field include the management and preparation of field before planting, and proper management of crop and field after planting.

*Fungal Growth and Mycotoxins Production: Types, Toxicities, Control Strategies… DOI: http://dx.doi.org/10.5772/intechopen.100207*

#### *3.1.1 Preparation and management of the field before planting*

Preparation of the field prior to planting is critical in controlling fungal invasion and the consequent production of mycotoxins. Deep plowing, tilling, production cycle, use of disease-resistant cultivars, crop rotation, use of high-quality seeds, etc. play important role. Deep plowing and tilling can be essentially used for the removal of remaining plant materials. Previous residues of crops which persist on the soil end up deteriorating and harboring soil-borne fungi, which increase their possibility of invading new crops. Plowing puts debris under the ground, making them not accessible to inhabitation by fungi. Tilling may also increase water availability to crops by minimizing the compressed layers of soil [48]. Additionally, rotation of crops prevents the build-up of fungi; it was reported that the production of mycotoxins is higher in lands where same crops are consecutively grown for years, as molds that may colonize a plant can occur from year to year if same crop was continuously planted [46–48]. Seeds for planting are also very important. Seeds with good quality contribute to the health of plants' growth to withstand fungal invasion.

#### *3.1.2 Management of crop and field after planting*

Facilitating the healthy plants growth after planting through implementing proper practices in the field and decreasing the stress on crops reduces fungal growth and production of mycotoxins [47, 49]. Fertilizers application improves the health of plants and maintains their disease and fungal resistance. Availability of nutrients is important for plant life and lack of proper nutrition of plant results in a break in the plant stem, exposing it to more invasion by fungi and other microorganisms [50]. Proper irrigation also has the capacity to prevent accumulation of mycotoxins via method and timing of irrigation. Proper timing can prevent drought stress, while the method of irrigation that control splashing can help prevent the spreading of fungi. The control of insect and weed is also important in preventing crop diseases and invasion by fungi [2, 51]. Fungicide application at proper doses can also help in controlling the fungal invasion and consequent production of mycotoxins.

#### *3.1.2.1 Early fungal detection as a control means*

Fungi presence does not necessarily indicate mycotoxin production; however, their presence implies an increased mycotoxin production risk if the conditions are suitable for the production of mycotoxin. Consequently, early detection of fungi which allows corrective measures can be very critical in controlling mycotoxin production [52]. When fungi are detected at early stages, the methods of decontamination (see [2]) in the field can be used to prevent fungal germination and growth, which in turn prevent subsequent production of mycotoxins.

#### *3.1.2.2 Biological control after planting*

After planting of crops, biological control measure largely includes the applying harmless species of fungi that compete with mycotoxigenic fungi, inhibiting their pathogenic activities. While this measure seems practically challenging, it presents safer control methods that are ecofriendly. This measure implies introducing a strain of harmless bio-agents, e.g. yeasts or bacteria, which compete with mycotoxigenic fungi for resources, thereby reducing their growth and ability to produce mycotoxin. For instance, *Aspergillus spp.* strains that do not produce aflatoxins are

applied as biological agents to compete with the strains that produce aflatoxins and prevent their dominance and subsequent aflatoxins production [53, 54]. A study reported that after applying non-aflatoxigenic strain of *Aspergillus parasiticus* on the soil in the field, significant reduction in the levels of aflatoxin was attained [55]. Same was the case after non-toxic strains of *Aspergillus flavus* were applied to cotton row. However, this biological control method has limitations that may discourage its wide application. First of all, the biological agent used may have impact on other natural occurring microorganisms. Secondly, non-toxigenic strains of fungi, even though they can help in reducing the production of mycotoxins, may produce other metabolic compounds that might be toxic to humans and animals. Thirdly, the non-toxigenic strains may result in underestimating the levels of mycotoxins, as they may have effects on the fungal metabolic pathways and cause the production of modified derivatives of mycotoxins [54]. Additionally, the ability to produce mycotoxins may be transferred from one fungi to another (a descendant) via nontoxigenic strains crossing with toxigenic strains, resulting in likely reproduction of successive fungi that produce mycotoxins [54].

#### *3.1.2.3 Chemical control after planting*

Use of fungicides as chemical control is one of the current most effective ways to proper control of crop invasion by fungi and consequent production of mycotoxins [53, 56]. Use of chemicals such as captan, mancozeb, cinnamaldehyde, citronella oil, tea tree oil, monocerin, sulfur, etc. has been recommended.

#### **3.2 Appropriate measures during harvest**

Another critical stage for controlling mycotoxin production is during harvest, where moisture plays the most crucial role for the protection of crops. Harvest should start after dry weather condition. Harvesting crops in wet weather may make them more vulnerable to the growth of fungi and subsequent mycotoxin production; also, keeping crops on the field for a long period of time can increase the risk of invasion by fungi, birds, rodents, pests, and insects, all of which can contribute to mycotoxin production through one way or the other [1]. It is important to prevent mechanical damage during harvest.

#### **3.3 Postharvest control and prevention**

#### *3.3.1 Appropriate storage*

Measures should be taken to limit fungal invasion and the production of mycotoxins before food products reach storage facility. If commodities are highly contaminated before reaching storage facility, it is difficult and more complicating to prevent further fungal or mycotoxins accumulation [47]. During storage, proper techniques should be applied to avoid fungal invasion and germination. Several fungi inhabit stored grains, especially fungal species that are infrequent in the field such as *Penicillium spp.* and *Aspergillus spp.*, whereas fungi in the field that require high water activity pose less significance during storage [57]. Several factors and storage conditions affect fungal growth and germination capacity during storage, especially temperature and aw. The fungi active in storage can grow at 70–90% relative humidity, and they usually thrive at temperatures of 10 to 40°C with 25–35°C range of optimum temperature [58]. Use of chemical preservatives, hygienic conditions, and storage time can also affect fungal growth and mycotoxin production. Temperature and water activity should be monitored and properly controlled during storage. The relative humidity should be kept below 70% throughout storage. The foods should be kept at low temperatures to reduce fungal activity during storage. The temperature of the stored food can be used as a good storage quality indicator.

#### *3.3.2 Chemical detoxification and decontamination*

Chemical methods make use of chemical treatments with oxidizing agents, reducing agents, alkalis, and acids which are synthetic or organic. The chemicals are employed in the detoxification of mycotoxins after adding the foods. Chemicals can be introduced through packing, fumigation, mixing, or immersion [59]. Chemical commonly used include formaldehyde, ozone, chlorinating agents, sodium bisulphite, hydrogen peroxide, hydrochloric acid, ammonium hydroxide, organic acids, and natural substances (e.g., spices, herbs, and their extracts) [59–61]. Treatment with chemical is effective in removing some mycotoxins, although they are mostly weak chemicals and most mycotoxins can be resistant to the chemicals. Ozone treatment is promising as it has the ability to degrade mycotoxins via reacting with bonds in the structure of mycotoxins, such as the double bonds in aflatoxin B1. By-products may form in the process [62, 63].

#### *3.3.3 Physical detoxification and decontamination*

Physical measures to control mycotoxins mostly comprise separating contaminated and damaged crops from wholesome crops using methods such as sorting, steeping, dehulling, washing, density segregation, sieve cleaning, etc., to reduce the mycotoxins levels [60, 64]. In physical process of decontamination, mycotoxins that are soluble in water can be removed partially from the grain outer surface using water or solutions of water [62]. Physical methods also include mycotoxins destruction and removal using irradiation and heat treatment [59]. Thermal processes including extrusion heating, radiofrequency, microwave, infrared, steam, boiling, etc. have been applied as innovative methods of mycotoxin decontamination [63]. Heat treatments that make use of a combination of the temperature conditions and time might give the most significant approach to control mycotoxins, however, most mycotoxins have heat stability and require very high temperatures and prolonged durations of processing for destruction, which may not be achieved in conventional food processing [64, 65] or destructive to the food constituents such as nutrients [63]. Non-thermal treatments like irradiation might be effective by partial lowering of mycotoxin levels, as the mycotoxins absorb energy of radiation and can be widely applied at industrial scale [62]. However, Irradiation is not widely applied due largely to public distrust of irradiated foods, since radiation has the ability to penetrate cells, causing DNA damage that results in mutations. In spite of that, the European Commission has approved 10 kGy dose as the maximum dose allowable for food application after it was demonstrated that this level poses no danger to humans [62].

Cold plasma is a recent novel non-thermal physical method used for the removal of fungi and mycotoxins. Cold plasma is ionized gas with partially ionized molecules and atoms with net charge approximately zero [66]. Cold plasma treatment caused the destruction of fungal DNA and cell wall, leading to the leakage of intracellular components [66–69]. Cold plasma partially or completely destroyed mycotoxins quickly [66, 70]. The efficiency of mycotoxins destruction mechanism is associated with their molecular structures, the nature of plasma, and subsequent interactions; destruction may be associated with the production of free radicals in the course of the treatment regimen, or the UV photons and ozone presence, or reactive electrons and ions [66]. Treatment with cold plasma is distinctive from conventional methods, as the mycotoxins can be rapidly decontaminated at ambient

#### *Fungal Reproduction and Growth*

pressure and temperature conditions without affecting the quality of the food [66]. However, some studies indicated that treatment with cold plasma may have effects on lipids, and it may be difficult to apply at large-scale industries, especially for the treatment of foods with irregular shape and bulky foods [71].

Photocatalytic detoxification is another emerging non-thermal technique used for mycotoxins removal from foods. The process involves chemical reaction initiated by photons absorption by solid photocatalyst, resulting in redox reactions on the photocatalytic material surface, leading to free radicals' formation which interact with the contaminants (mycotoxins) and helps degrade or convert them to lesser toxic substances via oxidation [72]. Several studies have reported photocatalytic detoxification effects on mycotoxins [72–75].

#### *3.3.4 Biological detoxification and decontamination*

Biological decontamination strategy makes use of microorganisms (algae, molds, yeasts, and bacteria). The microorganisms may bind, modify, or degrade the mycotoxins to lesser toxic compounds in some feed and foods through decarboxylation, hydrolysis, deamination, glucosylation, and/or acetylation [60]. Ochratoxin A can be converted to phenylalanine by some bacteria, plants, mold, and yeasts [76]. Some enzymes and microorganisms can be added to feed for mycotoxins degradation/detoxification in the ruminants' GI tracts. Yeasts and Lactic acid bacteria are mostly used for decontaminating mycotoxins as they can reduce their levels by binding to their cell surface or by converting them to lesser toxic substances [62]. Additionally, enzymatic catalysis can be used as they have promising applications in decontaminating mycotoxins [77].

#### **4. Conclusion**

Fungi commonly invade the commodities consumed by animals and humans, and due to their growth on the commodities, they produce low molecular weight secondary metabolites called mycotoxins. Environmental conditions such as temperature, water activity, and humidity affect mycotoxin production and fungal growth. Other factors such as pH, fungal strain, and substrate also play roles. The conditions that encourage the growth of fungi may not necessarily result in the production of mycotoxins. Common mycotoxins include aflatoxins, zearalenones (ZEAs), patulin, deoxynivalenol (DON), fumonisins, trichothecenes, sterigmatocystin (STC), citrinin, ergot alkaloids, ochratoxins, Alternaria toxins, tremorgenic mycotoxins, fusarins, cyclochlorotine, sporidesmin, 3-nitropropionic acid, etc. These toxins cause many health conditions in animals and humans, including death. A comprehensive approach starting from the field before planting, continuing throughout the entire food chain is required to control mycotoxin contamination. Good practices, such as proper field practices before and after planting, good harvest practices and postharvest handling, and proper drying and storage measures, help reduce mycotoxin contamination. Several physical, biological, and chemical decontamination methods can be used to reduce/eliminate mycotoxin levels. More studies are required to develop methods and techniques that can effectively reduce all mycotoxins in foods and feeds.

#### **Conflict of interest**

The authors declare no conflict of interest.

*Fungal Growth and Mycotoxins Production: Types, Toxicities, Control Strategies… DOI: http://dx.doi.org/10.5772/intechopen.100207*

#### **Author details**

Chinaza Godswill Awuchi1,2\*, Erick Nyakundi Ondari1 , Ifie Josiah Eseoghene2 , Hannington Twinomuhwezi2,3, Ikechukwu Otuosorochi Amagwula4 and Sonia Morya5

1 Department of Biochemistry, Kampala International University, Bushenyi, Uganda

2 School of Natural and Applied Sciences, Kampala International University, Kampala, Uganda

3 Department of Chemistry, Kyambogo University, Kampala, Uganda

4 Department of Food Science and Technology, Federal University of Technology Owerri, Owerri, Imo State, Nigeria

5 Department of Food Technology and Nutrition, Lovely Professional University, Phagwara, India

\*Address all correspondence to: awuchichinaza@gmail.com; awuchi.chinaza@kiu.ac.ug

© 2021 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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#### **Chapter 3**

## Fungal Growth and Pathology

*Ozlem Gulmez and Ozlem Baris*

#### **Abstract**

Fungi, an important group with a wide variety of species, shows spectacular development with their unique cell structures. Fungi survive in many different ecosystems with their reproductive abilities and metabolic features. Thanks to wide temperature and pH tolerances, fungi develop on organic and inorganic materials in all ecosystems they are in and maintain the existence of ecosystems by taking part in many cycles. However, examples of pathogens are also available. They are a group of organisms that are environmentally important, such as saprophytes and mutualists, but are pathogens for animals, especially plants. Fungi basically have two different cell structures: yeast, and molds. But some fungi have both of these structures. Depending on the temperature of the environment they are in, they can be found in yeast or mold structures, and fungi with this feature are called dimorphic fungi. Whether it is yeast, mold, or dimorphic fungi, they use their enzymes with high activity to benefit from the nutrients in the environment. Fungi can be easily grown in natural and synthetic media. Yeast can reproduce rapidly with their single-celled structure, while molds and mushrooms are very successful with their hyphae structures.

**Keywords:** fungal growth, pathology, reproduction

#### **1. Introduction**

Fungi are eukaryotic organisms thought to have about 4 million species [1]. Although the cell structures of fungi are similar to other eukaryotic cells, they differ from other cells by the presence of ergosterol in their cell membrane and chitin in their cell walls. Cell cytoplasm contains higher concentrations of salt and sugar than other eukaryotes. This regulates cell homeostasis and regulates the exchange of substances. Except for yeasts, most fungi have microscopic structures called hyphae, and these come together to form visible structures called mycelium. The hyphae have apical growth. In the apical growing parts of the hyphae, there are secretory vesicles called "Spitzenkörper" and Wooronin body organs that act as peroxisomes. Because of these properties of hyphae, fungi can live where other eukaryotic cells do not and can use various substrates [2, 3]. Fungi take part in many degradations, transformation, and cycle events in nature. Although they are heterotrophic creatures, they can survive as saprophytic, mutualistic, and parasitic. The fact, that they are found in all parts of the world and live in different environments is due to the superior reproductive abilities of fungi [4–6].

#### **1.1 Fungal reproduction**

Fungi can reproduce sexually and asexually. Asexual reproduction of fungi is carried out by vegetative reproduction through hyphae or by the spores they

produce. Sexual reproduction is; they form a diploid nucleus with the union of haploid spores, and the cycle continues with the germination of this nucleus. In fungi, asexual reproduction takes place more than sexual reproduction. This event increases the adaptive power of fungi and prevents the accumulation of any harmful mutations that may occur and their transmission from generation to generation. In addition, their chances of survival and competitive advantage are ensured [4, 5, 7].

Sexual reproduction in fungi takes place in three stages. In the first stage; haploid cells fuse, this is called plasmogamy. In the second stage; the fusion of two haploid nuclei, this event is karyogamy. The third stage is; the resulting diploid cells undergo meiosis to form haploid cells, and the cycle continues in this way [8]. These stages are summarized in **Figure 1**.

The association or non-union of haploid cells is determined by DNA. The sex of haploid cells is determined by a specific gene region in fungi. This region is known as the mating-type locus and is abbreviated MAT. MATs genetically determine the mating identity of fungi and stimulate the secretion of pheromones. Secreted pheromones provide communication between fungi and realize sexual intercourse [4, 9–11].

#### **1.2 Growth and development needs of fungi**

Fungi, like every living thing, need energy and food sources to complete their development and life cycles after sexual and asexual reproduction. These food sources are carbon, nitrogen, vitamins, and minerals. They also need suitable environmental conditions (such as pH, temperature, humidity, oxygen) to grow and develop [12–14].

Fungi can consume vegetable and animal carbon sources thanks to their hydrolytic enzymes. They can use monosaccharides and polysaccharides such as glucose, fructose, chitin, cellulose, hemicellulose, and lignin [15, 16]. Like all living things,

**Figure 1.** *Fungal reproduction.*

fungi need a nitrogen source for their growth and development, and fungi can metabolize many different nitrogen sources. Especially ammonium and glutamine are the first nitrogen sources they use. In addition, they can easily use other nitrogen sources [17].

Vitamins are cofactors of enzymes and growth factors of many organisms. Fungi need vitamins for their growth and development. Some of these vitamins are; thiamine, biotin, riboflavin, nicotinic acid, vitamin K and pantothenic acid [18].

Like many microorganisms, fungi can survive in varying environmental conditions and under various stress factors. They can survive and reproduce in extreme environments, such as the poles, in extremely cold regions, and in extremely hot regions such as deserts. Fungi are generally; grow better in warm, acidic, and aerobic environments, but they can survive in cold, alkaline, and anaerobic environments. Although the growth temperatures of the fungi are quite wide, the best growth is seen at 25°C. Fungi that live under the temperature at which they develop optimally are called psychrotolerant, and fungi that live at temperatures of 40°C and above are called thermotolerant fungi. Fungi that live in or are exposed to temperatures above 40°C can survive by protecting themselves from heat stress by producing heat shock proteins. Fungi can be found in yeast or mold structures depending on the temperature of the environment they are in, and fungi with this feature are called dimorphic fungi. One of the most important fungi showing this feature is *Histoplasma* sp. If the place where it is located in an environment of 25°C, it develops as a mold with a hyphae structure that can reproduce vegetatively, and as yeast if the environment is 37°C. This feature allows them to survive in different ecosystems and even to continue their generation [19]. The pH value, which is important for the realization of many biochemical reactions in all living things, is one of the important environmental conditions for fungi. Some fungi can survive and even reproduce at pH 1 and 13, which are extreme for many organisms. Most fungi survive and reproduce between pH 3 and 10. The optimum pH range is between 5 and 7 [20–22]. In addition, if the environment in which fungi are found in alkaline, they can achieve maximum growth by converting the pH of the environment to the optimum growth pH with the organic acids they secrete. Abiotic stress factors such as water, UV, and heavy metals affect the development of fungi as well as all organisms. In particular, UV-B radiation, which is more biologically harmful, negatively affects the growth and development of fungi [23].

Fungi are among the largest and most diverse groups of eukaryotic organisms. Because of their complex gene structure, the enzymes they produce, and their ability to use many different carbon sources, they, directly and indirectly, affect human life. They have been used for centuries as a food source and in the production process of many biotechnological products. Today, fungi are used in various fields such as antibiotics, enzyme technology, drug production, pigment production [24–26]. Although fungi are necessary for the survival of life on earth, they cause serious problems in most organisms. Fungi cause disease in humans, animals, and plants and cause the death of these organisms [27, 28]. Fungi infect many organisms with the secondary metabolites and mycotoxins they produce, even cause their extinction [29].

#### **1.3 Pathogenic fungi**

A fungal kingdom is a group that contains the most and most harmful plant pathogens. By infecting all tissues and organs of plants, they damage many herbaceous and woody plants with high economic value and nutritional properties. In cultivated plants such as corn, wheat, sugar beet, potato, banana; causes great harm to farmers by causing diseases such as root rot, wilt, stem softness, gall and rust.


#### **Table 1.**

*Some plant pathogenic fungi and infecting plants.*


**Table 2.**

*Diseases are caused by some pathogenic fungi in humans and animals.*

They also develop in stored grains and cause product loss. Also; high woody plants are infected by white rot and brown rot fungi, resulting in tissue deterioration and plant death. Plant pathogen fungi can reproduce both sexually and asexually in host plants [30–33]. **Table 1** shows the plants that some fungi cause disease.

Fungi cause infections not only in plants but also in humans and animals. Bees, insects, frogs, fish, and corals are some organisms affected by fungal infections. Fungi enter the body from the outer shells, trachea, and skin of these creatures and cause the death of these creatures. Fungal diseases have killed more than 1.6 million people annually. It is thought that pandemics caused by fungi may occur with global

#### *Fungal Growth and Pathology DOI: http://dx.doi.org/10.5772/intechopen.103109*

warming and climate change [34]. Because the stress tolerance and adaptation abilities of the fungi are very high, they have destroyed their existence on earth by infecting many different organism groups (**Table 2**). In humans, they cause skin infection, lung infection, and intestinal infection. They also cause diseases in animals and humans by reproducing sexually and asexually [35, 36].

### **2. Conclusions**

Apart from its use as food; the fungi which we use in the production of drugs, antibiotics, anticarcinogenic substances, pigments, alcohol, and biofuels, are indispensable elements for the continuation of our lives. As we stated in this publication, their high reproductive capacity and ability to survive in extreme conditions provide fungi with a competitive advantage and advantage over other organisms. These abilities give it the capability to live in the plant, animal, and human tissue-organs. If the development and growth demand of fungi, whether pathogenic or not, are known, we can make the most of these organisms and prevent the development of fungi that cause disease. This study will enable us to get to know fungi a little more closely and will enable us to take precautions against these organisms.

### **Conflict of interest**

The authors do not declare any conflict of interest.

#### **Author details**

Ozlem Gulmez\* and Ozlem Baris Faculty of Science, Biology Department, Ataturk University, Erzurum, Turkey

\*Address all correspondence to: ozlmg90@gmail.com

© 2022 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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