PENTOSE UTILIZATION AND TRANSPORT BY THE RUMINAL BACTERIUM PREVOTELLA-RUMINICOLA

Plant cell wall polysaccharides are primarily composed of hexose or hexose derivatives, but a significant fraction is hemicellulose which contains pentose sugars. Prevotella ruminicola B(1)4, a predominant ruminal bacterium, simultaneously metabolized pentoses and glucose or maltose, but the organism preferentially fermented pentoses over cellobiose and preferred xylose to sucrose. Xylose and arabinose transport at either low (2 muM) or high (1 mM) substrate concentrations were observed only in the presence of sodium and if oxygen was excluded during the harvest and assay procedures. An artificial electrical potential (DELTAPSI) or chemical gradient of sodium (DELTApNa) drove transport in anaerobically prepared membrane vesicles. Because (i) transport was electrogenic, (ii) a DELTApNa drove uptake, and (iii) the number of sodium binding sites was approximately 1, it appeared that P. ruminicola possessed pentose/sodium symport mechanisms for the transport of arabinose and xylose at low substrate concentrations. Pentose uptake exhibited a low affinity for xylose or arabinose (> 300 muM), and transport of xylose exhibited bi-phasic kinetics which suggested that a second sodium-dependent xylose transport system was present. Little study has been made on solute transport by Prevotella (Bacteroides) species and this work represents the first use of isolated membrane vesicles from these organisms.