Abstract
Lactobacillus plantarum ATCC 8014 grew on melibiose at 30C, but not at 37C, although it grew on galactose or lactose at either temperature. ATCC 8014 grown on lactose at 30 or 37C accumulated melibiose slowly, suggesting that melibiose may partly be transported by a lactose transport system. A lactose-negative mutant, NTG 21, derived from ATCC 8014 was isolated. The mutant was totally deficient in lactose transport, but retained normal melibiose transport activity. In NTG 21, the melibiose transport activity was induced by melibiose at 30C, but not at 37C. The transport activity itself was found to be stable for at least 3hr at 37C, suggesting that the induction process in the cytoplasm rather than the inducer entrance is temperature-sensitive in the organism. The organism also failed to form α-galactosidase at 37C when grown on melibiose. The enzyme synthesis, however, was induced by galactose in NTG 21 (and also by lactose in ATCC 8014) even at 37C, indicating that the induction of the enzyme is essentially not temperature-sensitive. In NTG 21, melibiose transport system and α-galactosidase were induced by galactose, melibiose and o-nitrophenyl-α-D-galactopyranoside when the strain was grown at 30C. Raffinose induced melibiose transport system only a little, while it was a good inducer for α-galactosidase. Inhibition studies revealed that galactose may be a weak substrate of the melibiose transport system; no inhibition was demonstrated with lactose and raffinose.
