**3.2 Wood decaying fungi**

Wood decaying or xylophagous fungi are those fungi that decompose wood dead or alive. These fungi in nature break down complex molecules of deadwood and branches and return their nutrients to the soil [2, 28]. Wood decaying fungi cause brown rot, soft rot, and white rot, with a different set of enzymes, and


#### **Table 1.**

*White-rot fungi and lignin degradation enzyme produced by them.*

based on the type of decay they cause they are classified as brown-rot fungi, softrot fungi, and white-rot fungi [29]. Brown-rot fungi produce hydrogen peroxide that breaks down cellulose and due to this the fungus removes all the cellulose compound from the wood and left the wood brown in color. Soft-rot fungi secrete the cellulolytic enzyme and break down the cellulose of the wood, these fungi are less aggressive than the white-rot fungi, whereas the white-rot fungi break both lignin and cellulose of the wood [5]. White-rot fungi produce laccase enzyme in higher concentrations and therefore they have been investigated for various use in mycoremediation, biofuel production, medical industries [5]. Fungi belonging to ascomycetes and basidiomycetes are generally white rot-fungi and have the potential to produce numerous enzymes of economic importance and hence white-rot fungi are extensively investigated to support the human lifestyle [29], however, these fungi also have adverse effects on our household wooden gadgets.

The wood and the leaf litter biomass have mostly lignocelluloses as the major components produced by the plant photosynthesis and represent the most abundant renewable resource in the soil [11]. Lignocellulose is consists of three types of polymers, cellulose, hemicellulose, and lignin which are strongly linked together by chemical bonds like non-covalent forces and by covalent cross-linkage, very small amount of lignocellulose produced by-product in agriculture or used in industries, and the remaining are considered as residue [11, 30]. Different microorganism degrades residue for the carbon as a source of energy, however, filamentous fungi evolved with the ability to degrade lignin to CO2 and other compounds as discussed in the above paragraph [31]. Some other lignocelluloses degrading fungi like brownrot and soft-rot fungi rapidly modify the lignin content and these fungi collectively play an important role in the carbon cycle [1, 11]. Apart from degrading lignin the white-rot fungi also degrade a variety of persistent environmental pollutants [30, 32, 33] like aromatic hydrocarbon, aliphatics hydrocarbon, cyanide compound, pesticides, fungicides, etc. This ability of white-rot fungi is only due to the strong oxidative activity and low substrate specificity of their ligninolytic enzyme (**Table 1**). As discussed above the white-rot fungi most commonly the macrofungi belongings to ascomycetes and basidiomycetes served as the integrated part in an ecosystem service as they produce various enzymatic mechanisms that degrade the wood and helps in maintaining the forest soil healths. Many fungi are the source of food for invertebrates in the forest, the organisms that feed on the fungi are termed as the fungivore. The ecological function of the fungi is strongly linked with the wood decay dynamics in the forest ecosystem [37], in **Table 1** the fungus listed with the enzymes are some most common enzymes produced by these fungi when come in contact with the woods and forest debris to degrade the recalcitrants forest wood and debris, the listed fungi in **Table 1** is mostly common in the forest ecosystem that acts as the decomposers.

#### **4. Role of fungi in human nutrition**

Fungi degrade different biomass and obtain nutrition for their growth and development. Fungi occur in diverse climates under different challenging conditions, and therefore they synthesized secondary metabolites to pace with the challenging threats of their life and the secondary metabolites have a broad range from antibiotic to mycotoxin. Fungi mainly use three pathways to synthesized metabolites: i. the mevalonic acid pathway (synthesize terpenoids, steroids, etc), ii. the shikimic acid pathway (synthesize aromatic amino acids, alkaloids, etc), and iii. The acetate pathway (synthesize polyketides, fatty acids, etc). Metabolites have

beneficial effects on human health like antioxidants, antibiotics, immunity booster, potent anticancer agents, and reduce stress, etc.

Mushrooms (filamentous fungi) with fruiting bodies show a huge number of pharmacological aspects in human health. Macrofungus like *Ganoderma sp.* and *Cordyceps sp.* used in the traditional medicines, *Ganoderma* (Reishi) mushroom has also been commonly referred to as the "mushroom of immortality", "tenthousand-year mushroom", "mushroom of spiritual potency", and "spirit plant by the Chinese monk [38, 39]. Generally, Mushrooms seemed to be used for food, medicine, poison, and in spiritual mushroom practices in religious rituals across the world since at least 5000 BC [40]. Gordon Wasson (father of modern Ethno mycology) supposed that the Soma plant used in religious ceremonies, over 4000 years ago, before the beginning of the Christian era, by the people who called themselves "Aryans" was a mushroom [41, 42]. The Vedic juice called "soma rasa" is said to bestow divine qualities on the soul of the consumer,


#### **Table 2.**

*Nutraceutical value of some edible mushrooms.*

even immortality [40, 42]. Mushrooms are considered one of the delicious foods and are commonly produced worldwide. They have been an essential part of the human diet and are used as both food and medicine for centuries. As shown in **Table 2**, they are a rich source of nutrients and bioactive compounds such as carbohydrates, fibers, proteins, vitamins, minerals, and have enormous medicinal attributes such as antibacterial, antiviral, antioxidant, anticancerous, and hypocholesterolemic which are valuable for human health [43]. The mushrooms are rich in protein and carbohydrate content, whereas low in lipid content. They contain essential amino acids, which help in meeting the needs of amino acids in the human body (**Figure 3**). They are also rich in many essential unsaturated fatty acids, such as linoleic and oleic acids, which are necessary for the proper functioning of the body. Apart from this, they contain many essential minerals, which are responsible for the proper metabolism of many pathways. Mushrooms being achlorophyllous therefore, they grow on decayed organic matters, rich in lignin, cellulose, and other important carbohydrates. It is economical, rich in pharmacological properties, easy to cultivate, requires low resources and area, and can be grown all over the world. Nutritional, medicinal, bioremediation, and biodegradation aspects of mushrooms are increasing day by day and have got strong focused in investigation for their hidden metabolic compounds [44, 45].
