Screening and engineering thermostable enzymes for deconstruction of lignocellulosic biomass

High enzyme cost for hydrolysis of lignocellulosic biomass is a major challenge for next generation fuel and chemical production from this renewable biomass. Large amounts of enzymes are needed and many problems about the degrading enzymes exist, such as high production cost, poor stability, and low tolerance to inhibitors generated during pretreatment and hydrolysis. Bacterial enzymes, especially the ones from thermophiles, are generally more robust compared with enzymes from fungi. Some Geobacilli, a genus of Gram-positive thermophilic bacteria, have demonstrated lignocellulolytic activities. In this study, we have screened about 150 Geobacillus strains for their production of thermostable lignocellulolytic enzymes, including cellulases, hemicellulases, and ligninolytic enzymes and characterized their enzymatic activity. Moreover, we developed a spore surface display system to construct super robust enzyme complexes to enhance their function under unfavorable conditions. This system also provides a platform to investigate the synergism between different enzymes in lignocellulose deconstruction.