Properties of a Streptococcus lactis strain that ferments lactose slowly

Abstract

Streptococcus lactis 7962, which ferments lactose slowly, has a lactose phosphoenolpyruvate-dependent phosphotransferase system and low phospho-β-galactosidase activity, in addition to high β-galactosidase activity. Lactose 6'-phosphate accumulated to a high concentration (>100 mM) in cells growing on lactose. In contrast, lactic streptococci, which ferment lactose rapidly and use only the lactose-phosphotransferase system for uptake, contained high phospho-β-galactosidase activity and low concentrations (0.9 to 1.6 mM) of lactose 6'-phosphate. It is concluded that rate-limiting phospho-β-galactosidase activity is primarily responsible for defective lactose metabolism in S. lactis 7962.