Analysis on the mechanism of the temperature-sensitive melibiose metabolism in Lactobacillus plantarum

L. plantarum can grow on melibiose when incubated at 30℃ but not when incubated at 37℃. In this study, the temperature sensitivity of melibiose metabolism was analyzed. The melibiose metabolism seemed to consist of the melibiose transport system and hydrolyzing enzyme, α-galactosidase. α-Galactosidase was induced with melibiose at 30℃ but not at 37℃. This enzyme induced at 30℃ hydrolyzed colorimetric substrate, α-ONPG at 30℃ and 37℃. On the other hand, lactose induced α-galactosidase at both temperatures. These findings suggested that the temperature sensitivity of melibiose metabolism was not due to the induction and/or function of α-galactosidase. Thus, the effect of temperature on induction and function of the melibiose transport system was examined. Cells grown on melibiose at 30℃ exhibited the rapid uptake of [(3)H] -melibiose at 30℃ and 37℃, while [(3)H] -melibiose was not taken up by the cells grown at 37℃. The induction of the melibiose transport system seemed to be temperature-sensitive because the transport system was not inactivated by exposure of the cells to 37℃ for 3 hours. In conclusion, the temperature sensitivity of melibiose metabolism was attributed to the temperature sensitivity of the induction of melibiose transport system.

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