**2. Mechanism of fungal degradation**

Fungi have numerous enzyme system and occur under the various climatic condition on a variety of substrates, the mode of nutritious in fungi is always heterotrophic, therefore being a heterotrophic organism they obtain their nutrition either through parasitic or saprotrophic mode and to do so, they employ a series of enzyme reaction on the substrate they grow since the biomass (dead bodies of plants and animals) are complex in chemical composition they are made available to fungi nutrition by converting it to the simpler form [3]. Generally, plant residues are lignocellulosic in nature which is a very complex molecule to digest by any organism, but fungi with the potential to produce enzymes that digest these residues to simpler, the mechanism of fungal degradations depend on the type of substrates and the enzymatic system, for example, lignin degradation by the white-rot fungi is an oxidative process and phenol oxidases are the key enzymes, manganese peroxidases, lignin peroxidases, laccase from the white-rot fungi have been found to play a significant role in lignin degradations [11] (discussed in Section 3.1.), white-rot fungi degrades lignin to use it as a sole carbon and energy source, and it is generally believed that lignin breaks down is necessary to gain access to cellulose and hemicelluloses of the substrates [11].

### **3. Fungi-mediated biodegradation**

Fungal has the potential to degrade organic materials naturally, considering this capacity of fungi to convert organic residue to different simple products are harnessed to produce valuable products for mankind's, which is used under control condition for the production of desired products by humans like production of bread, wine, medicine, and other industrial application, among this cultivation of edible and medicinal mushroom on organic residue is an example of fungal mediated biodegradation. The conversion of lignocellulosic residue to value products involves multi-steps which includes [11]:


Edible mushroom cultivation is a mediated fungal degradation for the production of non-consumable residue into the consumable source of nutrition riched

#### *Biodegradation by Fungi for Humans and Plants Nutrition DOI: http://dx.doi.org/10.5772/intechopen.99002*

food, mushrooms are fleshy and saprophytic fungus that utilizes wood trunks of trees, decaying organic matter, and damp soil rich in organic substances for their growth. Cultivation of mushrooms can be viewed as an effective way to utilize bioresources left in agricultural residues and environmental protection strategy [12, 13]. Cultivation of any type of mushroom implies principles of microbiology, environmental engineering, and solid-state fermentation in the conversion of domestic agricultural, industrial, forestry wastes into food for humans. *Pleurotus* mushrooms are simplest and are easily cultivable on the agric residue available on the agric farm, different types of substrate have been used for the cultivations to increase the yield [14–16]. *Pleurotus* is a genus of edible mushrooms widely cultivated throughout the world in a variety of substrates and conditions. This genus consists of more than 200 saprophytic species distributed worldwide in temperate and tropical environments and the most common species of *Pleurotus* genera (Oyster mushroom), are *P. ostreatus*, *P. djamor*, *P. citrinopileatus,* and *P. eryngii.* Among the common substrate used are wheat straw, sawdust, paddy straw, corn cob, sugarcane bagasse, ground nutshell, etc. [15, 17, 18]. *Pleurotus* produces the enzyme system to degraded the lignocellulosic components of the substrates and made them available for the mushroom for their metabolism which makes the mushroom a rich source of protein, dietary fiber, vitamins, and minerals [14, 19, 20]. Apart from oyster mushroom cultivation different variety have been adopted worldwide for the cultivation on the large scale both for medicine and the nutritions like species of *Agaricus, Lentinus*, *Calocybe*, *Volvariella*, *Auricularia*, *Ganoderma*, *Trametes,* etc., are some of the examples of fungal mediated biodegradation for production and utilization of wastes.
