Production of Butanol Directly from Hemicellulose through Secretory Expression of a Xylanase in Clostridium acetobutylicum

Butanol is an attractive second-generation biofuel as well as an important chemical. Production of butanol from lignocellulosic feedstock via consolidated bioprocessing has attracted increasing interest in recent years. However, this has been limited by the inefficient degradation of extracellular polysaccharides in butanol-producing strains. In this study, production of butanol directly from hemicellulose was achieved simply through overexpression of an indigenous xylanase in Clostridium acetobutylicum. The xylanase (XynB) encoded by CA_P0053 was highly soluble and fully secreted from C. acetobutylicum. The extracellular xylanase activity was increased 88-fold, and 4.03 g/L biobutanol was obtained from hemicellulose, which has been the highest yield yet reported from either hemicellulose or xylan. This study proved that the solventogenic C. acetobutylicum had great potential for consolidated production of biofuels. Understanding and applying its secretion mechanism will be of great significance in the future.