**4. Sources of secondary metabolites**

The major sources of secondary metabolites are plants (80% of secondary metabolite), bacteria, fungi, and many marine organisms (sponges, tunicates, corals, and snails) (**Table 1**) [8].


which threaten its survival in an unfavorable environment, such as drought, physical damage or infections. Resistance of plants to UV radiations is due to the phenolic compounds especially the phenylpropanoids present in them [17]. Phenolic compounds act as antioxidants protecting cells from oxidative stress scavenging of free radicals by hydrogen atom donation. The action of phenolic as neuroprotective [18], fungicidal [19], bactericidal [20] compounds and their anti-atherosclerosis [21] effects, and anticancer [22] activity is well documented.

An Introductory Chapter: Secondary Metabolites http://dx.doi.org/10.5772/intechopen.79766 7

Terpenoids are commercially important fragrance and flavoring agents [23]. Prenol and α-bisabolol are used in fragrance due to fruity odor and sweet floral aroma, respectively. Mono and sesqui terpenes are basis of natural perfumes and also of spices and flavorings in the food industry. The roles of terpenoids as pharmaceutical agents with activities such as antibacterial and antineoplastic are still under investigation. There are examples of diterpenes that exhibited *in vitro* cytotoxic, antitumor, and antimicrobial activities. Terpenes are vital for life in most organisms exerting metabolic control and mediating inter and intra species interactions, for example, manufacture compounds in response to herbivory or stress factors, and it has also been shown that flowers can emit terpenoids to attract pollinating insects and even attract beneficial mites, which feed on herbivorous insects. Cheng et al. [24] have reported that terpenes may act as chemical messengers influencing the expression of genes involved in plant defensive functions or influence gene expression of neighboring plants. Other second-

The conventional method of secondary metabolite production relies on extraction of metabolite, not production, from the tissues of plant by different phytochemical procedures like solvent, steam, and supercritical extraction. The recent developments in biotechnological methods like plant tissue culture, enzyme and fermentation technology have facilitated *in vitro* synthesis and production of plant secondary metabolites. The major processes include:

Cell or biocatalysts are confined within a matrix by entrapment, adsorption or covalent linkage. On addition of suitable substrate and provision on optimum physico chemical parameters, the desired secondary metabolites are synthesized. Immobilization with suitable bioreactor system provides several advantages, such as continuous process operation, but for the development of an immobilized plant cell culture process, natural or artificially induced

Plant cell and tissue cultures can be established routinely under sterile conditions from explants, such as plant leaves, stems, roots, meristems, etc., both for multiplication and extraction of secondary metabolites. Shoot, root, callus, cell suspension, and hairy root culture are used to synthesize metabolite of interest. Metabolites which are localized in multiple tissues

secretion of the accumulated product into the surrounding medium is necessary.

ary metabolite of plant origin and their functions is given in **Table 2** [25].

**4.2. Production of secondary metabolites from plants**

*4.2.1. Conventional*

*4.2.2. Immobilization*

*4.2.3. In vitro tissue, organ, and cell culture*

**Table 1.** Approximate number of known natural metabolites.

#### **4.1. Secondary metabolites of plants**

Plant secondary metabolites represent highly economically valuable products. These are used as high value chemicals such as drugs, flavors, fragrances, insecticides, dyes, etc. Plants are rich in a wide variety of secondary metabolites, such as tannins, terpenoids, alkaloids, and flavonoids, which have been found to have *in vitro* antimicrobial properties. Plants have an almost limitless ability to synthesize aromatic substances, most of which are phenols or their oxygen-substituted derivatives [9]. About 25,000 terpenoids are known as secondary compounds and are derived from the five-carbon precursor isopentenyl diphosphate (IPP). In total, around 12,000 known alkaloids are identified, and they possess one or more nitrogen atoms which are biosynthesized from amino acids. The 8000 known phenolic compounds are synthesized either through the shikimic acid pathway or through the malonate/acetate pathway [10].

Many alkaloids are used in medicine, usually in the form of salts. Some examples include vinblastine which has antitumor properties [11]; quinine which has antipyretics and antimalarial properties [12]; and reserpine which can be used to treat high blood pressure. Alkaloids are regarded as reserve materials for protein synthesis, as protective substances discouraging animal or insect attacks, and as plant stimulants or regulators or simply as detoxification products. Alkaloids currently in clinical use include the analgesics morphine and codeine, the anticancer agent vinblastine, the gout suppressant colchicine, the muscle relaxant tubocurarine, the antiarrhythmic ajmalicine, the antibiotic sanguinarine, and the sedative scopolamine.

*In vitro* studies have shown that natural phenols have antimicrobial [13], antiviral [14], antiinflammatory [15], and vasodilatory actions [16]. It protects the plant against adverse factors which threaten its survival in an unfavorable environment, such as drought, physical damage or infections. Resistance of plants to UV radiations is due to the phenolic compounds especially the phenylpropanoids present in them [17]. Phenolic compounds act as antioxidants protecting cells from oxidative stress scavenging of free radicals by hydrogen atom donation. The action of phenolic as neuroprotective [18], fungicidal [19], bactericidal [20] compounds and their anti-atherosclerosis [21] effects, and anticancer [22] activity is well documented.

Terpenoids are commercially important fragrance and flavoring agents [23]. Prenol and α-bisabolol are used in fragrance due to fruity odor and sweet floral aroma, respectively. Mono and sesqui terpenes are basis of natural perfumes and also of spices and flavorings in the food industry. The roles of terpenoids as pharmaceutical agents with activities such as antibacterial and antineoplastic are still under investigation. There are examples of diterpenes that exhibited *in vitro* cytotoxic, antitumor, and antimicrobial activities. Terpenes are vital for life in most organisms exerting metabolic control and mediating inter and intra species interactions, for example, manufacture compounds in response to herbivory or stress factors, and it has also been shown that flowers can emit terpenoids to attract pollinating insects and even attract beneficial mites, which feed on herbivorous insects. Cheng et al. [24] have reported that terpenes may act as chemical messengers influencing the expression of genes involved in plant defensive functions or influence gene expression of neighboring plants. Other secondary metabolite of plant origin and their functions is given in **Table 2** [25].

#### **4.2. Production of secondary metabolites from plants**

#### *4.2.1. Conventional*

**4.1. Secondary metabolites of plants**

**Table 1.** Approximate number of known natural metabolites.

NA – Data Not Available. Source: Bérdy [8].

**Source All known** 

6 Secondary Metabolites - Sources and Applications

pathway [10].

Plant secondary metabolites represent highly economically valuable products. These are used as high value chemicals such as drugs, flavors, fragrances, insecticides, dyes, etc. Plants are rich in a wide variety of secondary metabolites, such as tannins, terpenoids, alkaloids, and flavonoids, which have been found to have *in vitro* antimicrobial properties. Plants have an almost limitless ability to synthesize aromatic substances, most of which are phenols or their oxygen-substituted derivatives [9]. About 25,000 terpenoids are known as secondary compounds and are derived from the five-carbon precursor isopentenyl diphosphate (IPP). In total, around 12,000 known alkaloids are identified, and they possess one or more nitrogen atoms which are biosynthesized from amino acids. The 8000 known phenolic compounds are synthesized either through the shikimic acid pathway or through the malonate/acetate

**compounds**

Natural products Over one million 200,000–250,000 25,000–30,000 Plant kingdom 600,000–700,000 150,000–200,000 ~25,000 Microbes Over 50,000 22,000–23,000 ~17,000 Algae, lichens 3000–5000 1500–2000 ~1000

Higher plants 500,000–600,000 ~100,000 10,000–12,000

Animal kingdom 300,000–400,000 50,000–100,000 ~5000 Protozoa Several hundreds 100–200 ~50 Invertebrates ~100,000 NA ~500 Marine animals 20,000–25,000 7000–8000 3000–4000 Insects/ worms/ *etc.* 8000–10,000 800–1000 150–200 Vertebrates (mammals, fishes, amphibians, *etc.*) 200,000–250,000 50,000–70,000 ~1000

**Bioactives Antibiotics**

Many alkaloids are used in medicine, usually in the form of salts. Some examples include vinblastine which has antitumor properties [11]; quinine which has antipyretics and antimalarial properties [12]; and reserpine which can be used to treat high blood pressure. Alkaloids are regarded as reserve materials for protein synthesis, as protective substances discouraging animal or insect attacks, and as plant stimulants or regulators or simply as detoxification products. Alkaloids currently in clinical use include the analgesics morphine and codeine, the anticancer agent vinblastine, the gout suppressant colchicine, the muscle relaxant tubocurarine, the antiarrhythmic ajmalicine, the antibiotic sanguinarine, and the sedative scopolamine. *In vitro* studies have shown that natural phenols have antimicrobial [13], antiviral [14], antiinflammatory [15], and vasodilatory actions [16]. It protects the plant against adverse factors The conventional method of secondary metabolite production relies on extraction of metabolite, not production, from the tissues of plant by different phytochemical procedures like solvent, steam, and supercritical extraction. The recent developments in biotechnological methods like plant tissue culture, enzyme and fermentation technology have facilitated *in vitro* synthesis and production of plant secondary metabolites. The major processes include:

#### *4.2.2. Immobilization*

Cell or biocatalysts are confined within a matrix by entrapment, adsorption or covalent linkage. On addition of suitable substrate and provision on optimum physico chemical parameters, the desired secondary metabolites are synthesized. Immobilization with suitable bioreactor system provides several advantages, such as continuous process operation, but for the development of an immobilized plant cell culture process, natural or artificially induced secretion of the accumulated product into the surrounding medium is necessary.

#### *4.2.3. In vitro tissue, organ, and cell culture*

Plant cell and tissue cultures can be established routinely under sterile conditions from explants, such as plant leaves, stems, roots, meristems, etc., both for multiplication and extraction of secondary metabolites. Shoot, root, callus, cell suspension, and hairy root culture are used to synthesize metabolite of interest. Metabolites which are localized in multiple tissues


can be synthesized through unorganized callus or suspension cultures. But when the metabolite of interest is restricted to specialized part or glands in host plant, differentiated microplant or organ culture is the method of choice. Saponins from ginseng are produced in its roots, and hence *in vitro* root culture is preferred for saponin synthesis. Similarly, antidepressant hypericin and hyperforin are localized in foliar glands of *Hypericum perforatum*, which have

**S. No. Secondary metabolites Biological activity**

An Introductory Chapter: Secondary Metabolites http://dx.doi.org/10.5772/intechopen.79766 9

35. Capsacin Vanilla 36. Vanillin Rubber 37. Gutla percha Essential oils 38. Terpendids Spasmolytic 39. Papaverive Hypertensive 40. Ajmalicive Stimulant 41. Caffeine Antispasmadic

42. Birberine NA

The quantum of secondary metabolite production in cell cultures can be enhanced by treating plant cells with biotic and/or abiotic elicitors. Methyl jasmonate, fungal carbohydrates, and yeast extract are the commonly used elicitors. Methyl jasmonate is an established and effective elicitor used in the production of taxol from *Taxus chinensis* [27] and ginsenoside from *Panax ginseng* [28–32]. The most recently evolved and designed metabolic engineering can be

The production of metabolites through hairy root system based on inoculation with *Agrobacterium rhizogenes* has garnered much attention of late. The quality and quantity of secondary metabolite by hairy root systems is same or even better than the synthesis by intact host plant root [33]. In addition, stable genetic make up, instant growth in plant tissue culture media san phytohormones provides additional scope for biochemical studies. Root tips infected with *A. rhizogenes* are grown on tissue culture media [Murashige and Skoog's (MS) Gamborg's B5 or SH media] lacking phytohormones. Srivastava and Srivastava [34] have recently summarized the attempts to adapt bioreactor design to hairy root cultures; stirred tank, airlift, bubble columns, connective flow, turbine blade, rotating drum, as well as different gas phase reactors have all been used successfully. Genetic manipulation in hairy root culture for secondary metabolite production is being tried out. The established roots are screened for higher growth and production of metabolites. Transgenic hairy roots generated though *Agrobacterium rhizogenes* have not only paved way for plantlet gen-

eration but also for synthesis of desired product through transgenic hairy root cultures.

not been synthesized from undifferentiated cells [26].

**Table 2.** Biological activities of some secondary metabolites of plants.

employed to improve the productivity.

NA – Not Assessed.

Source: Ramawat and Merillon [25].


**Table 2.** Biological activities of some secondary metabolites of plants.

**S. No. Secondary metabolites Biological activity** 1. Pyrethrins Insecticidal 2. Nicotine Insecticidal 3. Rotenoids Insecticidal 4. Azadirachtin Insecticidal 5. Phytoecdysones Insecticidal 6. Baccharine Antineoplastic 7. Bruceantine Antineoplastic 8. Gsaline Antineoplastic 9. 3-Doxycolchicine Antineoplastic 10. Ellipticine Antineoplastic 11. 9-methoxyellipticine Antineoplastic 12. Fagaronive Antineoplastic 13. Tlarringtovinl Antineoplastic 14. Jandicine N-oxide Antineoplastic 15. Maytansive Antineoplastic 16. Podophyllotoxin Antineoplastic 17. Taxol Antineoplastic 18. Thalicarpine Antineoplastic 19. Tripdiolide Antineoplastic 20. Vinblastin Antineoplastic 21. Quinine Antimalarial 22. Digoxin Cardiac tonic 23. Diosgunin Antifertility 24. Morphine Analgesic

8 Secondary Metabolites - Sources and Applications

25. Thebaine Source of codeine 26. Suolpolanine Antihypertension 27. Alropine Muscle relaxant 28. Codeine Analgesic

29. Shikonin Dye, pharmaceutical

31. Rosamarinic acid Spice, antioxidant, perfume

30. Anthroquinones Dye, laxative

32. Jasmini Sweetner 33. Stevioside Saffron 34. Croun Chili

can be synthesized through unorganized callus or suspension cultures. But when the metabolite of interest is restricted to specialized part or glands in host plant, differentiated microplant or organ culture is the method of choice. Saponins from ginseng are produced in its roots, and hence *in vitro* root culture is preferred for saponin synthesis. Similarly, antidepressant hypericin and hyperforin are localized in foliar glands of *Hypericum perforatum*, which have not been synthesized from undifferentiated cells [26].

The quantum of secondary metabolite production in cell cultures can be enhanced by treating plant cells with biotic and/or abiotic elicitors. Methyl jasmonate, fungal carbohydrates, and yeast extract are the commonly used elicitors. Methyl jasmonate is an established and effective elicitor used in the production of taxol from *Taxus chinensis* [27] and ginsenoside from *Panax ginseng* [28–32]. The most recently evolved and designed metabolic engineering can be employed to improve the productivity.

The production of metabolites through hairy root system based on inoculation with *Agrobacterium rhizogenes* has garnered much attention of late. The quality and quantity of secondary metabolite by hairy root systems is same or even better than the synthesis by intact host plant root [33]. In addition, stable genetic make up, instant growth in plant tissue culture media san phytohormones provides additional scope for biochemical studies. Root tips infected with *A. rhizogenes* are grown on tissue culture media [Murashige and Skoog's (MS) Gamborg's B5 or SH media] lacking phytohormones. Srivastava and Srivastava [34] have recently summarized the attempts to adapt bioreactor design to hairy root cultures; stirred tank, airlift, bubble columns, connective flow, turbine blade, rotating drum, as well as different gas phase reactors have all been used successfully. Genetic manipulation in hairy root culture for secondary metabolite production is being tried out. The established roots are screened for higher growth and production of metabolites. Transgenic hairy roots generated though *Agrobacterium rhizogenes* have not only paved way for plantlet generation but also for synthesis of desired product through transgenic hairy root cultures.

#### **4.3. Secondary metabolites of microorganisms**

Microbial secondary metabolites are low molecular mass products with unusual structures. The structurally diverse metabolites show a variety of biological activities like antimicrobial agents, inhibitors of enzymes and antitumors, immune-suppressives and antiparasitic agents [7], plant growth stimulators, herbicides, insecticides, antihelmintics, etc. They are produced during the late growth phase of the microorganisms. The secondary metabolite production is controlled by special regulatory mechanisms in microorganisms, as their production is generally repressed in logarithmic phase and depressed in stationary growth phases. The microbial secondary metabolites have distinctive molecular skeleton which is not found in the chemical libraries and about 40% of the microbial metabolites cannot be chemically synthesized [35].

**Name of secondary metabolites Source of secondary** 

Trioxacarcins *S. ochraceus* and *S.* 

Oxohexaene and Cephalaxine *Streptomyces* sp. RM17*;* 

N-isopentyltridecanamide *Streptomyces labedae* ECR

Staurosporine *Streptomyces champavatii*

Thuricin CD 19 *B. thuringenesis DPC6431*

Bacillomycin *B. amyloliquefacins* FZB42,

Bacilysin 1 *B. subtilis* 168*, B. pumilus*

77

KV2

**Secondary metabolites of Actinobacteria**

Napyradiomycin (C-16 stereoisomers)

and Citreaglycon A

Citreamicin θ A, Citreamicin θ B,

**Secondary metabolites of** *Bacillus* **spp.**

**metabolites**

*bottropensis*

*Streptomyces* sp. RM42

Bacthurucin f4 *B. thuringenesis* sp. Fungicidal sub sp., *kurstaki*

*B. anthracis*

*B. subtilis*

GSB272

*B. amyloliquefaciens*

Resistomycin *S. corchorusii* HIV-1 protease inhibitor Shiono et al. [39] Himalomycins A and B *Streptomyces* sp. B6921 Antimicrobial Maskey et al. [40] Bonactin *Streptomyces* sp. BD21–2 Antibacterial Schumacher et al. [41]

Chinikomycins A and B *Streptomyces* sp. Antitumor and antiviral Li et al. [43] Daryamides *Streptomyces* sp. CNQ-085 Cytotoxic polyketides Asolkar et al. [44] Resistoflavine *S. chibaensis* Antibacterial Gorajana et al. [45] Chalcomycin A and terpenes *Streptomyces* sp. M491 Antibacterial Wu et al. [46]

Spiramycin *Streptomyces* sp. RMS6 Antibacterial Vijayakumar and

Coagulin *B. coagulans* Bactericidal, Bacteriolytic Le Marrec et al. [53]

Cerein *B. cereus* Bactericidal, bacteriolytic Bizani et al. [55] Megacin *B. megaterium* , Lisboa et al. [56] Thuricin S *B. thuringenesis* , Chehimi et al. [57]

Halobacillin 5b *B. licheniformis* Hemolytic, cytotoxic Kalinovskaya et al.

Bacilysocin *B. subtilis* Fungicidal, antibacterial Tamehiro et al. [61]

BUPM4

**Biological activities References**

An Introductory Chapter: Secondary Metabolites http://dx.doi.org/10.5772/intechopen.79766 11

Antitumor and antimalarial Maskey et al. [42]

Antibacterial Remya and

Antibacterial Thirumurugan et al.

Antimicrobial Cholarajan and

, Rea et al. [58]

Antifungal hemolytic Ramarathnam et al.

Antifungal, antibacterial Steinborn et al. [62]

Vijayakumar [48]

Malathi [50]

Vijayakumar [52]

Kamoun et al. [54]

[51]

[59]

[60]

*S. antimycoticus* Antibacterial Motohashi et al. [47]

*S. caelestis* Antibacterial Liu et al. [49]

#### *4.3.1. Features of microbial secondary metabolites*


#### **4.4. Applications of microbial secondary metabolites**

#### *4.4.1. Antibiotics*

The discovery of penicillin initiated the researchers for the exploitation of microorganisms for secondary metabolite production, which revolutionized the field of microbiology [5]. With the advent of new screening and isolation techniques, a variety of β-lactam-containing molecules [36] and other types of antibiotics have been identified. About 6000 antibiotics have been described, 4000 from actinobacteria (**Table 3**). In the prokaryotic group, unicellular bacteria *Bacillus* (**Table 3**) and *Pseudomonas* (**Table 3**) species are the most recurrent antibiotic producers. Likewise in eukaryotes, fungi are dominant antibiotic producers next to plants (**Table 3**). In the recent years, myxobacteria and cyanobacteria species have joined these distinguished organisms as productive species.

The pharmaceutical product, especially anti-infective derivatives comprise 62% antibacterials, 13% sera, immunoglobulins, and vaccines, 12% anti-HIV antivirals, 7% antifungals, and 6% nonHIV antivirals. There are over 160 antibiotics. *Streptomyces hygroscopicus* with over 200 antibiotics, *Streptomyces griseus* with 40 antibiotics, and *Bacillus subtilis* with over 60 compounds are the major contributors to the antibiotic market [7].

#### *4.4.2. Antitumor agents*

Natural product and its derivatives account for more than 60% of anticancer formulations. Actinobacteria derived antineoplastic molecules currently in use are actinomycin D,


**4.3. Secondary metabolites of microorganisms**

10 Secondary Metabolites - Sources and Applications

*4.3.1. Features of microbial secondary metabolites*

discovery and design of new drugs.

organisms as productive species.

*4.4.2. Antitumor agents*

further through chemical or biological transformation.

**4.4. Applications of microbial secondary metabolites**

pounds are the major contributors to the antibiotic market [7].

food, and environment.

*4.4.1. Antibiotics*

Microbial secondary metabolites are low molecular mass products with unusual structures. The structurally diverse metabolites show a variety of biological activities like antimicrobial agents, inhibitors of enzymes and antitumors, immune-suppressives and antiparasitic agents [7], plant growth stimulators, herbicides, insecticides, antihelmintics, etc. They are produced during the late growth phase of the microorganisms. The secondary metabolite production is controlled by special regulatory mechanisms in microorganisms, as their production is generally repressed in logarithmic phase and depressed in stationary growth phases. The microbial secondary metabolites have distinctive molecular skeleton which is not found in the chemical libraries and about 40% of the microbial metabolites cannot be chemically synthesized [35].

• The principle and process of natural fermentation product synthesis can be successfully scaled up and employed to maximize its application in the field of medicine, agriculture,

• The metabolite can serve as a starting material for deriving a product of interest, extended

• New analog or templates in which secondary metabolite serve as lead compounds will lead

The discovery of penicillin initiated the researchers for the exploitation of microorganisms for secondary metabolite production, which revolutionized the field of microbiology [5]. With the advent of new screening and isolation techniques, a variety of β-lactam-containing molecules [36] and other types of antibiotics have been identified. About 6000 antibiotics have been described, 4000 from actinobacteria (**Table 3**). In the prokaryotic group, unicellular bacteria *Bacillus* (**Table 3**) and *Pseudomonas* (**Table 3**) species are the most recurrent antibiotic producers. Likewise in eukaryotes, fungi are dominant antibiotic producers next to plants (**Table 3**). In the recent years, myxobacteria and cyanobacteria species have joined these distinguished

The pharmaceutical product, especially anti-infective derivatives comprise 62% antibacterials, 13% sera, immunoglobulins, and vaccines, 12% anti-HIV antivirals, 7% antifungals, and 6% nonHIV antivirals. There are over 160 antibiotics. *Streptomyces hygroscopicus* with over 200 antibiotics, *Streptomyces griseus* with 40 antibiotics, and *Bacillus subtilis* with over 60 com-

Natural product and its derivatives account for more than 60% of anticancer formulations. Actinobacteria derived antineoplastic molecules currently in use are actinomycin D,


treating obesity. *Firmicutes* and *Bacteroidetes* are the dominant beneficial bacteria present in the normal human gastrointestinal tract, and the latter was reported in lower numbers in constipation-predominant irritable bowel syndrome patients [38]. Carotenoids of microbial origin are used as food colorant, fish feeds, nutraceuticals, cosmetics, and antioxidants. Food colorant widely used is carotene derived from *Blakeslea trispora, Dunaliella salina* and lycopene from *B. trispora* and *Streptomyces chrestomyceticus, subsp*. *rubescens.* Astaxanthin produced from *Xanthophyllomyces dendrorhous* is an approved fish feed. Astaxanthin, lutein, β-carotene, zeaxanthin, and canthaxanthin are used as nutraceuticals due to their excellent antioxidant property. Docosahexaenoic acid (DHA) used in infant formula as nutritional supplements is

An Introductory Chapter: Secondary Metabolites http://dx.doi.org/10.5772/intechopen.79766 13

Enzymes produced from microorganism have annual sales of US \$ 2.3 billion enzymes that find application in detergents (34%), foods (27%), agriculture and feeds (16%), textiles (10%), and leather, chemicals, and pulp and paper (10%). The protease subtilisin used in detergents has an annual sale of \$ 200 million. The other major enzymes include glucose isomerase (100,000 tons) and penicillin amidase (60,000 tons). Nitrilase (30,000 tons) and phytase are amounting for \$135 million worth of production. *Streptomyces* glucose isomerase is used to isomerize D-glucose to D-fructose, to make 15 million tons per year of high fructose corn

The most important enzyme inhibitors are clavulanic acid, synthesized by *Streptomyces clavuligerus*, the inhibitor of β-lactamases. Some of the common targets for other inhibitors are glucosidases, amylases, lipases, proteases, and xanthine oxidase. Amylase inhibitors prevent absorption of dietary starches into the body, and hence can be used for weight loss [38].

Secondary metabolites find wide applications in the field of agriculture and animal health: kasugamycin and polyoxins are used as biopesticides; *Bacillus thuringiensis* crystals, nikkomycin, and spinosyns are used as bioinsecticides; bioherbicides (bialaphos) find application as bioherbicides; ivermectin and doramectin as antihelmintics and endectocides against worms, lice, ticks, and mites; ruminant growth promoters in the form of coccidiostats; plant hormones

Secondary metabolites branch out from the pathways of primary metabolism. Commercially,

Batch or fed-batch culture in submerged fermentation is employed for production of secondary metabolites. Inoculum is developed after careful strain improvement of producing organism. Initially, shake flasks culture is employed, and the culture which are in active growth

like gibberellins as growth regulators are the most common application [7].

important secondary and primary metabolic pathways are given in **Table 4**.

**4.5. Production of secondary metabolites from microorganisms**

derived from microalgae *Schizochytrium* spp. [7].

*4.4.4. Enzymes and enzyme inhibitors*

syrup, valued at \$1 billion [7].

*4.5.1. Liquid fermentation*

*4.4.5. Agricultural and animal health products*

**Table 3.** Secondary metabolites produced by microorganisms.

anthracyclines (daunorubicin, doxorubicin, epirubicin, pirarubicin, and valrubicin), bleomycin, mitosanes (mitomycin C), anthracenones (mithramycin, streptozotocin, and pentostatin), enediynes (calicheamicin), taxol, and epothilones [37].

Taxol is the nonactinobacterial molecule derived from plant *Taxus brevifolia* and endophytic fungi *Taxomyces andreanae* and *Nodulisporium sylviforme.* It interferes with microtubule breakdown, an essential event leading to cell division, thereby inhibiting rapidly dividing cancer cells. It is effective against breast and advanced form Kaposi's sarcoma. It is also found to exhibit antifungal activity against *Pythium*, *Phytophthora,* and *Aphanomyces*.

#### *4.4.3. Pharmacological and nutraceutical agents*

One huge success was the discovery of the fungal statins, including compactin, lovastatin, pravastatin, and others which act as cholesterol-lowering agents. Lovastatin is produced by *A. terreus.* Of great importance in human medicine are the immunosuppressants such as cyclosporin A, sirolimus (rapamycin), tacrolimus, and mycophenolate mofetil. They are used for heart, liver, and kidney transplants and were responsible for the establishment of the organ transplant field. Cyclosporin A is made by the fungus *Tolypocladium niveum*. Mycophenolate mofetil is a semisynthetic product of the oldest known antibiotic, mycophenolic acid, and is also made by a fungus. Sirolimus and tacrolimus are products of streptomycetes [7]. Metabolites of probiotic bacteria are considered as a remedy for controlling weight gain, preventing obesity, increasing satiety, prolonging satiation, reducing food intake, reducing fat deposition, improving energy metabolism, treating and enhancing insulin sensitivity, and treating obesity. *Firmicutes* and *Bacteroidetes* are the dominant beneficial bacteria present in the normal human gastrointestinal tract, and the latter was reported in lower numbers in constipation-predominant irritable bowel syndrome patients [38]. Carotenoids of microbial origin are used as food colorant, fish feeds, nutraceuticals, cosmetics, and antioxidants. Food colorant widely used is carotene derived from *Blakeslea trispora, Dunaliella salina* and lycopene from *B. trispora* and *Streptomyces chrestomyceticus, subsp*. *rubescens.* Astaxanthin produced from *Xanthophyllomyces dendrorhous* is an approved fish feed. Astaxanthin, lutein, β-carotene, zeaxanthin, and canthaxanthin are used as nutraceuticals due to their excellent antioxidant property. Docosahexaenoic acid (DHA) used in infant formula as nutritional supplements is derived from microalgae *Schizochytrium* spp. [7].

#### *4.4.4. Enzymes and enzyme inhibitors*

Enzymes produced from microorganism have annual sales of US \$ 2.3 billion enzymes that find application in detergents (34%), foods (27%), agriculture and feeds (16%), textiles (10%), and leather, chemicals, and pulp and paper (10%). The protease subtilisin used in detergents has an annual sale of \$ 200 million. The other major enzymes include glucose isomerase (100,000 tons) and penicillin amidase (60,000 tons). Nitrilase (30,000 tons) and phytase are amounting for \$135 million worth of production. *Streptomyces* glucose isomerase is used to isomerize D-glucose to D-fructose, to make 15 million tons per year of high fructose corn syrup, valued at \$1 billion [7].

The most important enzyme inhibitors are clavulanic acid, synthesized by *Streptomyces clavuligerus*, the inhibitor of β-lactamases. Some of the common targets for other inhibitors are glucosidases, amylases, lipases, proteases, and xanthine oxidase. Amylase inhibitors prevent absorption of dietary starches into the body, and hence can be used for weight loss [38].

#### *4.4.5. Agricultural and animal health products*

Secondary metabolites find wide applications in the field of agriculture and animal health: kasugamycin and polyoxins are used as biopesticides; *Bacillus thuringiensis* crystals, nikkomycin, and spinosyns are used as bioinsecticides; bioherbicides (bialaphos) find application as bioherbicides; ivermectin and doramectin as antihelmintics and endectocides against worms, lice, ticks, and mites; ruminant growth promoters in the form of coccidiostats; plant hormones like gibberellins as growth regulators are the most common application [7].

#### **4.5. Production of secondary metabolites from microorganisms**

Secondary metabolites branch out from the pathways of primary metabolism. Commercially, important secondary and primary metabolic pathways are given in **Table 4**.

#### *4.5.1. Liquid fermentation*

anthracyclines (daunorubicin, doxorubicin, epirubicin, pirarubicin, and valrubicin), bleomycin, mitosanes (mitomycin C), anthracenones (mithramycin, streptozotocin, and pentostatin),

Hydrogen cyanide *P. pseudoalcaligenes* P4 Antifungal Ayyadurai et al. [64]

Limonene and guaiol *Trichoderma viride* Antimicrobial Awad et al. [66] Tuberculariols *Tubercularia* sp. TF5 Anticancer Xu et al. [67] Oxaline *Penicillium raistricki* Anti-cell proliferation Sumarah et al. [68]

Roquefortine C *P. roqueforti; P. crustosum* Neurotoxin Kim et al. [70]; Xu

Pravastatin *Penicillium citrinum* Anticholesterolemics Gonzalez et al. [71]

**Biological activities References**

Enzyme inhibitor Dewick [65]

Antimalarial Stierle et al. [69]

Lewis et al. [63]

et al. [67]

phytopathogens

Taxol is the nonactinobacterial molecule derived from plant *Taxus brevifolia* and endophytic fungi *Taxomyces andreanae* and *Nodulisporium sylviforme.* It interferes with microtubule breakdown, an essential event leading to cell division, thereby inhibiting rapidly dividing cancer cells. It is effective against breast and advanced form Kaposi's sarcoma. It is also found to

One huge success was the discovery of the fungal statins, including compactin, lovastatin, pravastatin, and others which act as cholesterol-lowering agents. Lovastatin is produced by *A. terreus.* Of great importance in human medicine are the immunosuppressants such as cyclosporin A, sirolimus (rapamycin), tacrolimus, and mycophenolate mofetil. They are used for heart, liver, and kidney transplants and were responsible for the establishment of the organ transplant field. Cyclosporin A is made by the fungus *Tolypocladium niveum*. Mycophenolate mofetil is a semisynthetic product of the oldest known antibiotic, mycophenolic acid, and is also made by a fungus. Sirolimus and tacrolimus are products of streptomycetes [7]. Metabolites of probiotic bacteria are considered as a remedy for controlling weight gain, preventing obesity, increasing satiety, prolonging satiation, reducing food intake, reducing fat deposition, improving energy metabolism, treating and enhancing insulin sensitivity, and

exhibit antifungal activity against *Pythium*, *Phytophthora,* and *Aphanomyces*.

enediynes (calicheamicin), taxol, and epothilones [37].

**Table 3.** Secondary metabolites produced by microorganisms.

**Name of secondary metabolites Source of secondary** 

**Secondary metabolites of** *Pseudomonas* **spp.**

12 Secondary Metabolites - Sources and Applications

Lovastatin *Monascus ruber;*

Benzomalvin C *Penicillium raistrickii*,

**Secondary metabolites of Fungi**

**metabolites**

Pseudomonine *P. stutzeri* KC Competitive inhibition of

*Aspergillus terreus*

*Penicillium* sp. SC67

*4.4.3. Pharmacological and nutraceutical agents*

Batch or fed-batch culture in submerged fermentation is employed for production of secondary metabolites. Inoculum is developed after careful strain improvement of producing organism. Initially, shake flasks culture is employed, and the culture which are in active growth


the nature of solid phase used [7]: (a) solid culture of one support-substrate phase solid phase and (b) solid culture of two substrate-support phase solid phase. The advantages of solidstate fermentation in relation with submerged fermentation include: energy requirements of the process are relatively low, since oxygen is transferred directly to the microorganism. Secondary metabolites are often produced in much higher yields, often in shorter times, and

It is important here to note our own experience of deriving actinobacterial secondary metabolite. Actinobacteria from terrestrial and marine habitats were screened for their antimicrobial activity. The bioactive metabolites were extracted and purified by thin layer and column chromatography, and the structure of the metabolite was elucidated by UV-spectrometry, FT-IR, mass spectrum analysis, and NMR. The derived metabolites staurosporine, octa-valinomycin, methyl-4,8-dimethylundecanate, and N-isopentyltridecanamide are known for their biologi-

This review emphasizes the importance of secondary metabolites from various sources like plants, microorganisms including bacteria, actinobacteria, and fungi and its classification, production and applications in various fields. Since there is a constant and crucial requirement for new pharmaceutical agents to fight cancers, cardiac disorders, pests, cytotoxic, mosquitoes, infectious diseases, and autoimmune disorders of both animals and plants as climate changes provide conditions favorable to repeated outbreaks of these events. The battle against any disease is a vibrant symmetry between advances in chemotherapy and natural selection on infectious or invasive agents. If the scientific community is to put constant importance in this never ending effort, then new sources of bioactive secondary metabolites with novel activities must be found. Secondary metabolites are one of their essential means of growth and defense, and these metabolites are readily available for discovery. Secondary metabolites with noteworthy biological activity are considered as an alternative to most of the synthetic

often sterile conditions are not required [7].

drugs and other commercially valuable compounds.

\*

\*Address all correspondence to: rvijayakumar1979@gmail.com

, Alagappan Cholarajan<sup>2</sup>

1 Department of Biotechnology, SRM Institute of Science and Technology, Tamilnadu, India

2 P.G. Department of Microbiology, Srinivasan College of Arts and Science, Perambalur,

3 Research Department of Microbiology, Bharathidasan University Constituent College,

, Suresh S.S. Raja<sup>3</sup>

and

An Introductory Chapter: Secondary Metabolites http://dx.doi.org/10.5772/intechopen.79766 15

cal activity (**Figure 2**).

**5. Conclusion**

**Author details**

Perambalur, India

India

Durairaj Thirumurugan1

Ramasamy Vijayakumar<sup>3</sup>

**Table 4.** Intermediate from primary metabolism and their secondary metabolite derivatives.

**Figure 2.** Chemical structures of actinobacterial secondary metabolites. (a) Staurosporine, (b) octa-valinomycin, (c) methyl-4,8-dimethylundecanate, and (d) N-isopentyltridecanamide from actinobacteria. Source: Cholarajan and Vijayakumar [52]; Cholarajan [72]; Thirumurugan et al. [73].

phase are transferred to a small fermenter and later into a larger fermenter with production medium. Several parameters, like medium composition, pH, temperature, and agitation and aeration rate, are controlled. An inducer such as methionine is added to cephalosporin fermentations, phosphate is restricted in chlortetracycline fermentation, and glucose is avoided in penicillin or erythromycin fermentation.

#### *4.5.2. Solid-state fermentation*

Solid-state fermentation, defined as a microbial culture that develops on the surface and at the interior of a solid matrix and in the absence of free water, holds an important potential for the production of secondary metabolites. Two types of SSF can be distinguished, depending on the nature of solid phase used [7]: (a) solid culture of one support-substrate phase solid phase and (b) solid culture of two substrate-support phase solid phase. The advantages of solidstate fermentation in relation with submerged fermentation include: energy requirements of the process are relatively low, since oxygen is transferred directly to the microorganism. Secondary metabolites are often produced in much higher yields, often in shorter times, and often sterile conditions are not required [7].

It is important here to note our own experience of deriving actinobacterial secondary metabolite. Actinobacteria from terrestrial and marine habitats were screened for their antimicrobial activity. The bioactive metabolites were extracted and purified by thin layer and column chromatography, and the structure of the metabolite was elucidated by UV-spectrometry, FT-IR, mass spectrum analysis, and NMR. The derived metabolites staurosporine, octa-valinomycin, methyl-4,8-dimethylundecanate, and N-isopentyltridecanamide are known for their biological activity (**Figure 2**).
