2-39: Metabolic engineering of C. thermocellum for biofuel production

Clostridium thermocellum is a thermophilic anaerobic bacterium that specializes in the rapid solubilization and fermentation of crystalline cellulose to products that include ethanol. As such, it is considered a prime candidate for consolidated bioprocessing, the process by which a single organism is responsible both for the hydrolysis and fermentation of plant biomass for biofuel production. Recent advances in genetic tool development in this organism have greatly accelerated metabolic engineering efforts to reroute central metabolism toward biofuel production. We have constructed C. thermocellum deletion mutants that constrain carbon and electron flux, resulting in strains that produce substantially more ethanol than the wild type. Phenotypic characterization of these strains gives insight into central metabolism of C. thermocellum and suggests future paths for the engineering of more efficient biofuel production from plant biomass. We are further improving these strains using both rational and random approaches. Heterologous gene expression is being used to expand the repertoire of enzymatic reactions available to C. thermocellum for efficient fuel production. The engineered organisms are also being improved through strain evolution. Genome resequencing of these evolved strains will lead to improved understanding of the bottlenecks that limit metabolic flux and growth upon modification of central metabolism.