S56: Engineering synthetic microbial consortia for consolidated bioprocessing of lignocellulosic biomass

Inspired by the ubiquitous existence and remarkable metabolic capabilities of synergistic microbial communities in nature, we are exploring an alternative strategy for microbial engineering and synthetic biology - design and construction of synthetic microbial consortia consisting of different specialists that coordinate to accomplish a complicated task. Our current application focus is to integrate saccharification and fermentation capabilities for enabling one-step “consolidated” bioprocessing (CBP), a potential breakthrough technology that can lead to large-scale and cost-effective production of lignocellulosic biofuels or chemicals. Our general design includes one cellulolytic member responsible for hydrolyzing hemicellulose and cellulose into mono and oligosaccharides; one hexose fermenting member for converting glucose monomer and oligosaccharides into desired products; and one pentose fermenting member for converting pentose sugars. In our initial work, using a consortium of cellulolytic fungus Trichoderma reesei and genetically modified Escherichia coli, we demonstrate direct conversion of microcrystalline cellulose and pretreated corn stover to isobutanol, a promising next-generation biofuel. Without costly nutrient supplementation, we achieved titers up to 1.86 g/L and yields up to 62% of the theoretical maximum, which represent the highest reported to date for conversion of cellulosic substrates to next-generation biofuels. In addition, we show that cooperator-cheater dynamics lead to stable coexistence of the two consortium members and provide a mechanism for tuning population composition. In parallel, we engineered a consortium consisting of two E. coli specialists for converting lignocellulose-derived hexose and pentose sugars to isobutanol. Under certain conditions, the biculture performed better than each monoculture on defined sugar mixtures or enzymatic hydrolysates from real biomass.