The effect of lignin S/G ratio on consolidated bioprocessing (CBP) fermentation performance

Recent published data has found the ratio of syringyl and guaiacyl in the lignin of natural Populus trichocarpa variants to influence the release of total sugars through enzymatic hydrolysis. In general, it was found that glucose and xylose release varies in correlation with the S/G ratio, and in the case of glucose also in relation to the total lignin content (Studer et al, 2011, PNAS, 108(15): 6300-6305). A higher S/G ratio is generally expected to improve biomass degradation. The goal of the current research is to establish the relation between lignin S/G content and biomass deconstruction by microbial cultures under a consolidated bioprocessing approach. We analyzed five poplar (Populus trichocarpa) individuals with similar and average lignin content, but with a wide spectrum of S/G ratios undergoing fermentation by three naturally cellulolytic strains of Clostridium thermocellum. Following this screening process we narrowed our selection to two poplar samples with either very high or with very low S/G ratios and one microorganism that carried out fast biomass deconstruction. The results investigate microbial hydrolysis and fermentative performance as well as the structural and compositional characteristics of the biomass and residues that may influence the microbial activity.