The influence of the genes hfsB and hfsD in high ethanol production in T. thermossacharolyticum

Abstract

Second-generation ethanol production from lignocellulose will help meet today's energy, environmental and climate challenges. To carry out lignocellulosic biomass fermentation, several research groups are studying the usage of the bacterium Clostridium thermocellum, one of the best cellulose solubilizers among all known microorganisms. However, for this process to be economically viable, C. thermocellum must produce ethanol with high yield and titer, and work to date has only been partially successful. Much better ethanol yield and titer has been achieved with the distantly related Thermoanaerobacterium saccharolyticum. Results in T. saccharolyticum point to a critical role for the genes encoded by the hfsABCD operon. These genes encode hydrogenases, which transfer electrons in the sugar to ethanol pathway to protons, and allow for redox balanced fermentation. It was observed that the hfsC and hfsD genes are essential to obtain high ethanol yield, and seem to have their activity down-regulated by the presence of the hfsA and hfsB genes. This project seeks to investigate the mechanism by which the presence of the hfsD gene leads to a higher level of ethanol and a lower level of H2 and aims to understand how this gene is related to the other subunits of this same operon. Therefore, a series of genetic manipulations will be carried out in T. thermosaccharolyticum and an investigation whether HfsB has a regulatory role or if HfsD interacts with other proteins will be performed. If proven to be a key element in increasing ethanol production, we will be able to optimize the strains obtained so far and move closer to making second-generation biofuels an even more competitive alternative. (AU)