SIMULTANEOUS UPTAKE AND UTILIZATION OF GLUCOSE AND XYLOSE BY CLOSTRIDIUM-THERMOHYDROSULFURICUM

Growth studies of Clostridium thermohydrosulfuricum Rt8.B1 demonstrate d that glucose and xylose were used simultaneously when supplied toget her at nonlimiting concentrations in pH-controlled batch culture. Unde r conditions of hyperbolic growth, both catabolite repression and indu cer exclusion were absent. Glucose did not repress xylose metabolism ( i.e. xylose permease and xylose isomerase genes were expressed in the presence of glucose and were not subject to catabolite inhibition when glucose was added to cultures growing on high concentrations of xylos e). The kinetics of glucose and xylose utilisation indicated that sepa rate systems were present for the uptake of these substrates when supp lied together. Glucose utilisation was biphasic, indicating high- and low-affinity systems for glucose uptake. Xylose utilisation was direct ly proportional to the xylose concentration, suggesting a facilitated diffusion mechanism was operative for uptake.