Glucose transport by the phosphoenolpyruvate:mannose phosphotransferase system in Lactobacillus casei ATCC 393 and its role in carbon catabolite repression.

A 2-deoxy-D-glucose-resistant mutant of a pLZ15-cured derivative of Lactobacillus casei ATCC 393 was isolated on agar medium containing 10 mM 2-deoxy-D-glucose and 5 g lactose I-1. The mutant was impaired in the main glucose transport mechanism, a PTSman-type system. Additionally a proton-motive-force-dependent glucose permease was detected. The growth response and the sugar consumption rates of the wild-type and the PTSman-deficient mutant suggested that the mutated element of the complex IIABCman was, in the wild-type, responsible for a strong repression by glucose and mannose of the lactose and ribose assimilation genes, while assimilation of galactose was only weakly repressed. It is postulated that they are regulated by a different mechanism of catabolite repression.