Deconstruction of plant biomass by the hyperthermophilic anaerobe Caldicellulosiruptor without conventional pretreatment

Thermophilic organisms offer special advantages for the conversion of lignocellulosic biomass to biofuels and bioproducts. The use of complex feedstocks often requires pretreatment, involving exposure to acid or base at high temperature and the addition of hydrolytic enzymes that partially digest the plant cell walls. Enzymatic pretreatment is expensive and often prohibitive for the production of low value commodity products, such as ethanol. Members of the Gram-positive bacterial genus Caldicellulosiruptor are anaerobic thermophiles with optimum growth temperatures between 65°C to 78°C and are the most thermophilic cellulolytic organisms known. Members of this genus vary in their ability to use unpretreated substrates including populus and switchgrass and do so in the absence of a cellulosome. We have used genetic methods developed in our lab to generate deletions of genes predicted to be involved in biomass utilization including celA, a family-48/family-9 glycosyl hydrolase and a cluster of genes involved in pectin utilization. We report the effect of these mutations on biomass deconstruction and their use to identify key plant cell wall components that contribute to plant biomass recalcitrance.