In these situations, the presence of a NFO or NAD(P)H-dependent H2ase may intermittently

alleviate these high NADH/NAD+ ratios through generation of reduced Fd pools or H2 production, respectively, albeit it would decrease reducing equivalents for mTOR inhibitor ethanol production. While some attempts to increase H2 and/or Tideglusib ethanol yields through genetic engineering have been successful in a number of lignocellulolytic organisms (reviewed elsewhere; [101]) engineering of strains discussed here has only been marginally successful. Heterologous expression of Zymomonas mobilis pyruvate decarboxylase and Adh in C. cellulolyticum increased cellulose consumption and biomass production, and decreased lactate production and pyruvate overflow due to a more efficient regulation of carbon and electron flow at the pyruvate branchpoint [102]. However, despite higher levels of

total ethanol produced, ethanol yields (per mol hexose consumed) actually decreased when compared to the wild-type strain. Similarly, deletion of PTA in C. thermocellum drastically reduced acetate production, but had minimal impact on lactate or ethanol production [103]. This suggests that genome content alone cannot exclusively dictate see more the extent of end-product yields observed in literature, and thus growth conditions must be optimized in order to moderate regulatory mechanisms that direct carbon and electron flux. This could only be attained through a thorough understanding of regulatory mechanisms that mediate gene and gene-product expression and activity levels under various growth conditions through a combination of genomics, transcriptomics, proteomics, metabolomics, and enzyme characterization. Conclusions Fermentative bacteria offer the potential to convert biomass into renewable biofuels such as H2 and ethanol through consolidated bioprocessing. However, Acetophenone these bacteria display highly variable, branched catabolic pathways that divert carbon and electrons towards unwanted end

products (i.e. lactate, formate). In order to make fermentative H2 and/or ethanol production more economically feasible, biofuel production yields must be increased in lignocellulolytic bacteria capable of consolidated bioprocessing. While the cellulolytic and, to a lesser extent, H2 and ethanol producing capabilities of cellulolytic bacteria have been reviewed [8, 9, 44], a comprehensive comparison between genome content and corresponding end-product distribution patterns has not been reported. While reported end-product yields vary considerably in response to growth conditions, which may influence gene and gene product expression and metabolic flux, we demonstrate that composition of genes encoding pyruvate catabolism and end-product synthesis pathways alone can be used to approximate potential end-product distribution patterns.