Pentose transport by the ruminal bacterium Butyrivibrio fibrisolvens

Butyrivibrio fibrisolvens is a fibrolytic ruminal bacterium that degrades hemicellulose and ferments the resulting pentose sugars. Washed cells of strain D1 accumulated radiolabelled xylose (Km = 1.5 microM) and arabinose (Km = 0.2 microM) when the organism was grown on xylose, arabinose, or glucose, but cultures grown on sucrose or cellobiose had little capacity to transport pentose. Glucose and xylose inhibited transport of each other non-competitively. Both sugars were utilized preferentially over arabinose, but since they did not inhibit transport of arabinose, it appeared that the preference was related to an internal metabolic step. Although the protonmotive force was completely abolished by ionophores, cells retained some ability to transport pentose. In contrast, the metabolic inhibitors iodoacetate, arsenate, and fluoride had little effect on protonmotive force but caused a large decrease in intracellular ATP and xylose and arabinose uptake. These results suggested that high-affinity, ATP-dependent mechanisms were responsible for pentose transport and hexose sugars affected the utilization of xylose and arabinose.