Biology, Fiber-Degradation, and Enzymology of Anaerobic Zoosporic Fungi

Abstract

Anaerobic zoospore-producing fungi that inhabit the gastrointestinal tract of herbivores, especially ruminants, have recently been discovered. These fungi have been isolated from the rumen, hind gut, and the feces 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 and the types of thalli that develop from the zoospores. Their life cycle consists of a zoospore that encysts and develops into a vegetative thallus with zoosporangia, which at times become resting sporangia. These fungi produce a wide range of active hydrolytic enzymes, notably cellulases and xylanases, that provide them with the potential to degrade the major structural polysaccharides in plant cell walls. Their cellulases are among the most active reported to date and solubilize both amorphous and highly ordered cellulose. Their esterases are active against both feruloyl and p-coumaroyl arabinoxylans, which provides an advantage in degrading poorly biodegradable cell walls. They degrade lignin-containing cell walls, but do not metabolize the lignin moiety. Rhizoids of vegetative thalli penetrate cell walls, and they are better able than bacteria or protozoa to attack recalcitrant tissues and weaken the textural strength of plant material.

Lignocellulose biodegradation: Fundamentals and applications

“…These fungi produce active polymer degrading enzymes, including cellulases and xylanases (Hodrova et al 1998). Their cellulases are among the most active reported to date and able to solubilise both amorphous and crystalline cellulose (Wubah et al 1993). These fungi can be used in situations where process principles and design necessitate anaerobic conditions.…”

Fungi open new possibilities for anaerobic fermentation of organic residues

“…Furthermore, anaerobic fungi are known to form co-cultures with ruminal methanogenic archaea which utilize the fungal hydrogen production [13]. The role of ruminal fungi in the degradation of plant fibres has been studied extensively [9,10,[14][15][16][17]. The fungi can attach to the most lignified plant tissues [18] and are in turn followed by the ingress of cellulolytic bacteria which then gain access to the interior of otherwise less fermentable plant material.…”

Primary sequence and enzymic properties of two modular endoglucanases, Cel5A and Cel45A, from the anaerobic fungus Piromyces equi The EMBL accession numbers for the sequences reported in this paper are AJ277482 and AJ277483.

“…At least five genera of anaerobic fungi have been described to date including Neocallimastix, Orpinomyces, Piromyces, Caecomyces and Anaeromyces. The polysaccharide hydrolases produced by anaerobic fungi are amongst the most active that have been described to date ; they are capable of degrading a wide range of polysaccharides and can completely solubilize both amorphous and highly crystalline cellulose (Li & Heath, 1993 ; Selinger et al, 1996 ;Wubah et al, 1993). Unlike aerobic fungi, anaerobic fungi produce large, multienzyme cellulasehemicellulase complexes, similar to the cellulosome of Clostridium thermocellum (Ali et al, 1995 ; Dijkerman et al, 1997 ; Fanutti et al, 1995 ; Hazlewood & Gilbert, 1998 ; Teunissen et al, 1993 ;Wilson & Wood, 1992).…”