BIOLOGY, FIBER-DEGRADATION, AND ENZYMOLOGY OF ANAEROBIC ZOOSPORIC FUNGI

Anaerobic zoospore-producing fungi that inhabit the gastrointestinal t ract of herbivores, especially ruminants, have recently been discovere d. These fungi have been isolated from the rumen, hind gut, and the fe ces of ruminants. Thirteen species, belonging to five genera, of these fungi have been assigned to the class Chytridiomycetes. These species are classified according to the number of flagella on the zoospores a nd the types of thalli that develop from the zoospores. Their life cyc le consists of a zoospore that encysts and develops into a vegetative thallus with zoosporangia, which at times become resting sporangia. Th ese fungi produce a wide range of active hydrolytic enzymes, notably c ellulases arid xylanases, that provide them with the potential to degr ade die major structural polysaccharides in plant cell walls. Their ce llulases are among the most active reported to date and solubilize bot h amorphous and highly ordered cellulose. Their esterases are active a gainst both feruloyl and p-coumaroyl arabinoxylans, which provides an advantage in degrading poorly biodegradable cell walls. They degrade l ignin-containing cell walls, but do not metabolize the lignin moiety. Rhizoids of vegetative thalli penetrate cell walls, and they are bette r able than bacteria or protozoa to attack recalcitrant tissues and we aken the textural strength of plant material.