Molecular breeding of Clostridia for butanol production from rice straw

Biobutanol produced by Clostridium spp. can be used as a biofuel and/or chemical feedstock. For cost-effective and sustainable production of biobutanol, an untapped biomass such as rice straw could be used as a substrate. Rice straw, which is composed of cellulose, hemicellulose, and lignin, is cheap and abundant. However, the utilization of rice straw is limited because butanol-producing clostridia cannot degrade cellulose, which is the major carbon source in lignocellulose. To achieve butanol production from lignocellulose, cellulose needs to be hydrolyzed to dior monosaccharides that can then be metabolized by Clostridium spp. In this study, we developed a system for butanol production from rice straw using a co-culture of cellulose-degrading Clostridium thermocellum and butanol-producing Clostridium saccharoperbutylacetonicum. In addition, we showed that β-glucosidase enhances butanol production from rice straw, and identified promoters that may be used for high-level expression of the β-glucosidase gene to increase productivity.