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 Lacto bacillus pentosus. Uptake of D-xylose was not driven by the proton motive f orce generated by malolactic fermentation and required D-xylose metabolism. The kinetics of D-xylose transport were indicative of a low-affinity facil itated-diffusion system with an apparent K-m of 8.5 mM and a V-max of 23 nm ol min(-1) mg of dry weight(-1). In two mutants of L. pentosus defective in the phosphoenolpyruvate:mannose phosphotransferase system, growth on D-xyl ose 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 co mplemented after expression of the L. curvatus manB gene encoding the cytop lasmic 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, Th ese two species could transport and metabolize D-xylose after transformatio n with plasmids which expressed the D-xylose-catabolizing genes of L. pento sus, xylAB. L, casei and L. plantarum mutants resistant to 2-deoxy-D-glucos e were defective in EIIMan activity and were unable to transport D-xylose w hen transformed with plasmids containing the xylAB genes. Finally, transpor t of D-xylose was found to be the rate-limiting step in the growth of L, pe ntosus and of L. plantarum and L, casei ATCC 393 containing plasmids coding for the D-xylose-catabolic enzymes, since the doubling time of these bacte ria on D-xylose was proportional to the level of EIIMan activity.