AbstractThe cellulolytic and ethanologenic bacterial community is a promising candidate for the production of bioethanol from lignocellulose. In this study, by artificially changing the ratio of Clostridium thermocellum in the cellulolytic consortium H, ethanol production was increased by 72.7%. Metatranscriptomic analysis was used to elucidate the contribution of Clostridium thermocellum to ethanol production. A comprehensive analysis of genes mapped to the Clostridium thermocellum ATCC 27405 genome was performed; the identified gene expression differences related to cellulosic ethanol pathways were carefully studied. The results indicated that the majority of genes involved in lignocellulose degradation, sugar transport, cellodextrin breakdown, glycolysis, and ethanol synthesis were up-regulated in C. thermocellum when added to H (HCt). More than 18 cellulosome-related genes had 15-fold or greater increased expression. The results illustrate the role of C. thermocellum in the cellulolytic consortium H and HCt and provided useful information for identifying genes and preferred pathways. These results will aid in the metabolic and genetic engineering of bacterial strains for more efficient biofuel production.