Transport of D-xylose in Lactobacillus pentosus, Lactobacillus casei, and Lactobacillus plantarum:: Evidence for a mechanism of facilitated diffusion via the phosphoenolpyruvate:: Mannose phosphotransferase system

We have identified and characterized the D-xylose transport system of Lactobacillus pentosus. Uptake of D-xylose was not driven by the proton motive force generated by malolactic fermentation and required D-xylose metabolism. The kinetics of D-xylose transport were indicative of a low-affinity facilitated-diffusion system with an apparent K-m of 8.5 mM and a V-max of 23 nmol min(-1) mg of dry weight(-1). In two mutants of L. pentosus defective in the phosphoenolpyruvate:mannose phosphotransferase system, growth on D-xylose was absent due to the lack of D-xylose transport. However, transport of the pentose was not totally abolished in a third mutant, which could be complemented after expression of the L. curvatus manB gene encoding the cytoplasmic EIIBMan component of the EIIMan complex. The EIIMan complex is also involved in D-xylose transport in L. casei ATCC 393 and L. plantarum 80, These two species could transport and metabolize D-xylose after transformation with plasmids which expressed the D-xylose-catabolizing genes of L. pentosus, xylAB. L, casei and L. plantarum mutants resistant to 2-deoxy-D-glucose were defective in EIIMan activity and were unable to transport D-xylose when transformed with plasmids containing the xylAB genes. Finally, transport of D-xylose was found to be the rate-limiting step in the growth of L, pentosus and of L. plantarum and L, casei ATCC 393 containing plasmids coding for the D-xylose-catabolic enzymes, since the doubling time of these bacteria on D-xylose was proportional to the level of EIIMan activity.