Abstract
The most abundant aromatic biopolymer on earth Lignin is extremely recalcitrant to degradation. It creates a barrier to solutions or enzymes by linking to both hemicellulose and cellulose preventing the penetration of lignocellulolytic enzymes into the interior lignocellulosic structure. Global attention has been gained by fungi owing to the potential use of their versatile enzymes for agriculture, medicines, industries and bioremediation. The combination of extracellular ligninolytic enzymes, mediators, organic acids and accessory enzymes make some of the basidiomycete white-rot fungi to be able to degrade lignin efficiently. This review describes remediation of lignocelluloses by fungi, properties of fungi, their spatial distribution and the mechanisms of action which render them attractive candidates in biotechnological applications like biopulping, animal feed, genetic engineering and space exploration.
TopProperties Of Lignocelluloses
The word lignin is derived from Latin word ‘Lignum’ meaning wood. It embodies three components of lignocellulosic biomass in addition to cellulose and hemicellulose. Lignin, the second most abundant natural substance in nature after cellulose is produced approximately 5 x 106 metric tons annually through industrial processes (Mai, Majcherczyk, & Huttermann, 2000). Lignin, most abundant renewable source of aromatic polymers owes it degradation mandatory for carbon recycling. Lignin chemically is a cross-linked macromolecule derived from the oxidative coupling of monolignols, mainly hydroxycinnamyl alcohols which are three main components comprising of p-coumaryl, coniferyl and synapyl alcohols. The composition of lignin is plant-specific, with molecular weight and linkage motifs varying according to plant species and environmental factors.
Key Terms in this Chapter
Biorefineries: Co-production of a variety of biologically-based products such as food, feed, materials, chemicals and energy i.e fuels, power, heat from biomass.
Fungal Degradation: It is a beneficial activity of fungi in carrying out biodegradation using chemical substances as carbon and energy source for metabolism, thereby breaking down larger molecules to smaller ones.
Polymers: Compounds with high molecular weight consisting of repeated linked units, each a relatively light, similar and simple molecule. e.g. natural compounds like lignin and cellulose and many synthetic organic materials used as plastics and resins.
Biotechnological Applications: It is the use of living systems and organisms to develop or make products. Applications include the production of certain drugs, synthetic hormones, and bulk foodstuffs as well as the bioconversion of organic waste and the use of genetically altered bacteria in the cleanup of oil spills.
Genetic Engineering: A set of technologies used to change the genetic makeup of cells, including the transfer of genes within and across species boundaries to produce improved or novel organisms.
Extracellular Enzymes: These are enzymes that are secreted by a cell which function outside of that cell, where their function is to break down complex macromolecules into smaller units to be taken up by the cell for growth and assimilation. These enzymes degrade complex organic matter such as cellulose and hemicellulose into simple sugars that enzyme-producing organisms use as a source of carbon, energy, and nutrients.
Fungi: Plural for fungus which is a group of unicellular, multicellular, or syncytial spore-producing organisms including yeasts and molds, as well as multicellular fungi that produce familiar fruiting forms known as mushrooms.
Biopulping: It is a type of industrial biotechnology. It uses natural fungus to convert wood chips to paper pulp.