A Because of insolubility, fungal degradation occurs either

A diverse range of microorganisms,
primarily fungi and bacteria have been identified over the years which
producing lignocellulolytic enzymes. They depolymerize lignocellulose via series
of hydrolytic or oxidative enzymes including lignin peroxidase, magnese
peroxidase, versatile peroxidise, laccases, endoglucanases, cellobiohydrolases and
?-glucosidases. These enzymes have been broadly studied in submerged and solid culture
processes ranging from flask shake to large scale. Since bacteria lacking
lignin peroxidases thus biodegradation of lignocellulose in bacteria is
essentially a slow process. Grasses are more susceptible than wood for actinomycete
and play a substantial role in the humification processes together with
bacteria in soils and composts. Bacterial
enzymes can cleave alkyl-aryl ether bonds in oligomeric and monomeric aromatic
compounds, released by degradation of lignin through fungi. Thus lignocellulose
biodegradation by prokaryotes is of ecological significance while by fungi is
of commercial importance.

Degradation of lignocellulose by
fungi include white
rot and brown rot fungi. White rot fungi degrade lignin more quickly and
extensively than any other microorganisms. Because of insolubility, fungal degradation occurs either
exocellularly, in association with the outer cell envelope layer or
extracellularly. Two enzymatic systems are found; a hydrolytic system in which
hydrolases degrade polysaccharide and a distinctive oxidative and
extracellular ligninolytic system, which degrades lignin and unlocks phenyl
rings. Despite a large number of microorganisms which are producing
lignocellulolytic enzyme only few have been studied extensively. In the
commercial production of hemicellulases and cellulases Trichoderma reesei and its mutants are extensively employed. Most of the microorganism used in the production
of lignocellulytic enzymes are acting mainly on cellulose or hemicellulose. Only
few group of microorganisms has evolved with the ability to degrade lignin. It has been reported that T. reesei produce hemi and cellulolytic enzymes significantly but
unable to degrade lignin. The most efficient lignin degrading microbes are
basidiomycetes, a white rot fungi Phanerochaete
chrysosporium, producing plentiful amounts of unique set of lignocellulytic
enzymes which efficiently degrade lignin into CO2. Other white-rot fungi such as Daedalea flavida, Phlebia fascicularia, P.
floridensis and P. radiate have been found to selectively degrade lignin in
wheat straw. So these fungi are used to selectively remove the lignin leaving
the other components almost intact. Some lignocellulose degrading brown-rot fungi rapidly
depolymerize cellulosic materials while only modifying lignin. In addition to lignin, white-rot fungi are able to degrade
a variety of persistent environmental pollutants, such as chlorinated aromatic compounds,
heterocyclic aromatic hydrocarbons, various dyes and synthetic high polymers.
This degradative ability of white-rot fungi is due to the strong oxidative
activity and low substrate specificity of their ligninolytic enzymes.
Nevertheless, it is clear that some soft-rot fungi can degrade lignin, because
they erode the secondary cell wall and decrease the content of acid-insoluble material
(Klason lignin) in angiosperm wood. Soft rot fungi typically attack higher
moisture, and lower lignin content materials. 

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