P25: Anaerobic fungi as a novel platform for ethanol production from cellulosic biomass

Anaerobic fungi (AF) reside in the rumen, hindgut, and feces of herbivores and combine the invasiveness and hyphal growth of aerobic fungi with the fermentative mode of metabolism of anaerobic bacteria. Here we demonstrate that an anaerobic fungal isolate (Orpinomyces sp. strain C1A) is a prolific and versatile biomass degrader that could be utilized for ethanol production from cellulosic biomass. Strain C1A effectively utilized cellulosic and hemicellulosic fractions in a wide range of untreated bioenergy crops (Switchgrass), crop residues (corn stover, sorghum forage, energy cane, alfalfa), mixed native prairie grasses, and mixed grasses from marginal lands, with biomass degradation ranging between 18.6- 39.3% (28.7-47.5% of fermentable sugars) in switchgrass and corn stover, respectively. Implementation of various pretreatment schemes, adjustments to the inoculum: substrate ratio, and immobilization of C1A on solid surfaces lead to marked improvements in the rate and extent of biomass degradation, with values reaching 40.8-60.9% of plant biomass (53.9-75.2% of fermentable sugars) in switchgrass and cornstover, respectively. In monoculture, strain C1A produced acids (lactate, formate, and acetate) and low concentrations of ethanol from plant biomass. However, in co-culture with an ethanologenic strain, a significant fraction of the degraded plant biomass was redirected towards ethanol production. Thus, these cocultures are capable of direct, high titer ethanol production from several different types of lignocellulosic biomass in a consolidated process, which does not require the addition of enzymatic preparations and could proceed without pretreatment steps. The economic and environmental implications of this novel biomass to ethanol conversion process are discussed.