PENTOSE TRANSPORT BY THE RUMINAL BACTERIUM BUTYRIVIBRIO-FIBRISOLVENS

Butyrivibrio fibrisolvens is a fibrolytic ruminal bacterium that degra des hemicellulose and ferments the resulting pentose sugars. Washed ce lls of strain D1 accumulated radiolabelled xylose (K-m = 1.5 mu M) and arabinose (K-m = 0.2 mu M) when the organism was grown on xylose, ara binose, or glucose, but cultures grown on sucrose or cellobiose had li ttle capacity to transport pentose. Glucose and xylose inhibited trans port of each other non-competitively. Both sugars were utilized prefer entially over arabinose, but since they did not inhibit transport of a rabinose, it appeared that the preference was related to an internal m etabolic step. Although the protonmotive force was completely abolishe d 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 i n intracellular ATP and xylose and arabinose uptake. These results sug gested that high-affinity, ATP-dependent mechanisms were responsible f or pentose transport and hexose sugars affected the utilization of xyl ose and arabinose.