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

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American Society for Microbiology

RESUMO

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 Km of 8.5 mM and a Vmax 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.

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