Anaerobic gut fungi: Advances in isolation, culture, and cellulolytic enzyme discovery for biofuel production

Abstract

Anaerobic gut fungi are an early branching family of fungi that are commonly found in the digestive tract of ruminants and monogastric herbivores. It is becoming increasingly clear that they are the primary colonizers of ingested plant biomass, and that they significantly contribute to the decomposition of plant biomass into fermentable sugars. As such, anaerobic fungi harbor a rich reservoir of undiscovered cellulolytic enzymes and enzyme complexes that can potentially transform the conversion of lignocellulose into bioenergy products. Despite their unique evolutionary history and cellulolytic activity, few species have been isolated and studied in great detail. As a result, their life cycle, cellular physiology, genetics, and cellulolytic metabolism remain poorly understood compared to aerobic fungi. To help address this limitation, this review briefly summarizes the current body of knowledge pertaining to anaerobic fungal biology, and describes progress made in the isolation, cultivation, molecular characterization, and long-term preservation of these microbes. We also discuss recent cellulase- and cellulosome-discovery efforts from gut fungi, and how these interesting, non-model microbes could be further adapted for biotechnology applications.

Mapping the membrane proteome of anaerobic gut fungi identifies a wealth of carbohydrate binding proteins and transporters

“…Whereas their tremendous biotechnological potential is unquestionable, isolation and cultivation of the gut fungi under laboratory conditions has proven challenging and only a relatively small number of strains have been isolated to date. Moreover, very little is known about the membranes and membrane proteins of these early branching fungi, and the extreme AT-richness of their genomes have precluded high quality genomic data from being obtained [22, 23]. …”

Early-branching gut fungi possess a large, comprehensive array of biomass-degrading enzymes

“…1), making them rich untapped sources for previously unidentified lignocellulolytic enzymes. However, their strict anaerobic lifestyle, complex nutritional requirements, and culture recalcitrance have severely hindered early attempts at isolation, exploitation, and molecular characterization (10). …”

Coexpression of rumen fungal xylanase and bifunctional cellulase genes in Escherichia coli

“…Rumen fungi produce a wide range of plant cell wall degrading enzymes that enable them to utilize fibrous plant biomass efficiently. Studies on the functional transfer of rumen fungal genes to tractable bioprocessing hosts are rapidly emerging 27 . In this study, xylanase encoding xynA-7 and cellulase and lichenase encoding bifunctional celA-5 were cloned into E. coli and we performed partial characterization of XynA-7 and CelA-5.…”