FERMENTATION OF D-XYLOSE BY CLOSTRIDIUM-BUTYRICUM LMG-1213T1 IN CHEMOSTATS

Clostridium butyricum LMG 1213t1 was able to grow on D-xylose and L-arabinose in a minimal medium. In a chemostat in carbon limitation, the same fermentation balance (when corrected for the difference in carbon atoms) was obtained on D-xylose as on glucose in the pH range 5.5-7.0. Per mole D-xylose consumed, 1.74 mol H-2 was produced, which was equal to the H-2 production on glucose previously reported. By varying the dilution rate, the molar growth yields remained less than half these on glucose. From a critical literature survey, we propose that this was caused by an additional ATP expenditure for the active transport of D-xylose across the cell membrane. From our data we calculated that 1 mol ATP was required for the transport of D-xylose. With higher D-xylose concentrations, the butyrate production and molar growth yield Y(xylose) gradually decreased, but the H-2 production remained constant. On glucose-xylose mixtures (10 g l-1 total sugar), the fermentation of D-xylose was not inhibited by glucose under the conditions tested. The molar growth yields increased linearly with the weight percentage of glucose in the carbon source, while the H-2 production was not affected.