Abstract: Improved yields of biofuels and other chemicals are obtained by culturing a cellulolytic microorganism, such as Clostridium phytofermentans, Clostridium sp. Q.D, or Clostridium biocatalysts thereof in modulated amounts of vitamins, such as thiamine or nicotinic acid. Provided are methods to increase yields of ethanol and other fermentation products through vitamin supplementation. Recombinant microorganisms with altered metabolic pathways that obviate the need to modulate media components during hydrolysis and fermentation of biomass are also described.