초록
Sixteen combinations of seven growth nutrients, namely α-cellulose, yeast extract (YE), urea, CaCl<SUB>2</SUB>.2H<SUB>2</SUB>O, MgCl<SUB>2</SUB>.6H<SUB>2</SUB>O, FeSO<SUB>4</SUB>.6H<SUB>2</SUB>O and vitamins, were studied to improve direct cellulose fermentation by Clostridium thermocellum DSM 1237 under carbon-excess conditions. Varied nutrient compositions improved cellulose fermentation conditions for C. thermocellum and displayed two major types of effects: a general growth enhancement effect and a carbon-flux shifting effect. Different concentrations of the four most influential nutrients (YE, α-cellulose, CaCl<SUB>2</SUB> and MgCl<SUB>2</SUB>) resulted in enhanced yields of ethanol or H<SUB>2</SUB>. High ethanol yields, high ethanol to acetate (E/A) ratios, and low acetate and H<SUB>2</SUB> yields were obtained when YE, α-cellulose and CaCl<SUB>2</SUB> were present at high concentrations, in combination with low concentrations of magnesium. Vitamins were identified as a relatively less influential nutrient, but high concentrations of vitamins supported enhanced yields of acetate and H<SUB>2</SUB>. High urea and YE in combination with low MgCl<SUB>2</SUB> concentrations enhanced cellulose utilization per unit mass of cells and cell-specific yields of both ethanol and H<SUB>2</SUB>. Volumetric yields for ethanol and H<SUB>2</SUB> were improved by 2.3-fold (76.5 mM) and 2.04-fold (71.22 mmol per liter), respectively, compared with the basic combination. The highest hydrogen yield (1.64 mol/mol glucose) was obtained in the combination with the lowest ethanol yields while the lowest hydrogen yielding combination had the highest ethanol yield of 1.36 mol/mole glucose, representing 68% of the theoretical maximum for ethanol. The culture conditions determined by this study can be optimized further for enhanced production of either ethanol or H<SUB>2</SUB> by direct cellulose fermentation.