White and Brown Rot Fungi as Decomposers of Lignocellulosic Materials and Their Role in Waste and Pollution Control
Along with bacteria, fungi contribute to essential ecological functions, such as recycling of organic carbon 'trapped' in cellulose and lignin, an ability that is the hallmark of white and brown rot fungi. The mycelium of some of these fungi produces digestive enzymes that speed up the breakdown of lignocellulosic wastes. In doing so, they promote the recycling of nutrients and help maintain the ecosystem equilibrium. Some fungi are parasites and mutualistic symbionts, and obtain their nutrients from living organisms. Others are saprotrophs, which rely on dead organisms for their nutrition. Among fungal saprotrophs, basidiomycete white and brown rot fungi are the main decomposers of lignocellulosic materials and will be the focus of this chapter. White and brown rot fungi are important contributors to mitigation of environmental pollution. They decompose lignocellulosic residues and wastes generated from agricultural and forestry operations, releasing the carbon stored in plant and wood cell walls. Collected residues, along with purposely grown energy crops, can be converted into value added products, such as biofuels and novelty chemicals, and the application of white and brown rot fungi and their enzymes can significantly improve process efficiency. On the negative side, these fungi cause damage to wooden structures constructed for human use. However, the knowledge gained on the growth conditions, physiology, biochemistry and enzymology of white and brown rot fungi in an effort to minimise or control the damage caused by them to useful wooden structures is offering opportunities to employ these fungi and their enzymes to degrade a wide range of environmental contaminants and pollutants from industrial and other sources. The chapter will describe the processes of decomposition of lignocellulosic materials by white and brown rot fungi, and then highlight the advances being made in the application of these fungi and their enzymes in waste and pollution minimisation. Limitations to developing effective technologies will also be discussed.