THE INFLUENCE OF LIMITING AND NONLIMITING GROWTH-CONDITIONS ON GLUCOSE AND MALTOSE METABOLISM IN LACTOCOCCUS-LACTIS SSP LACTIS STRAINS

Three strains of Lactococcus lactis ssp. lactis, a dairy strain 65.1, a type strain ATCC 19435, and a mutant AS 211, were grown on glucose a nd on maltose under chemostat conditions. When the culture was shifted from glucose-limiting to non-limiting conditions, the product shifted from mixed acids to lactate. Mixed acids were obtained in all maltose cultures; however, an enhanced lactate formation was observed in 1943 5 and AS 211. An inorganic-phosphate (P-i)-dependent maltose phosphory lase activity was found to be responsible for the initial conversion o f maltose. The activation of maltose phosphorylase by P-i was strain-s pecific. When growth was on maltose under non-limiting conditions, a c orrelation was found between high initial maltose phosphorylase and be ta-phosghoglucomutase activities and lactate production. No such corre lation was observed in maltose-limited cells. In glucose-grown cells u nder non-limiting conditions, home-fermentative lactate formation coin cided with high concentrations of fructose 1,6-bisphosphate (Fru1,6P(2 )) and pyruvate (Pyr) and low concentrations of phosphoenolpyruvate (P Pyr). Under limiting conditions, mixed acid formation coincided with l ow concentrations of Fru1,6P(2) and Pyr and high concentrations of PPy r. In maltose-grown cells there was no correlation between intracellul ar intermediary metabolite concentrations and product formation. There fore, in addition to intracellular intermediary metabolite concentrati ons, the product formation on maltose is suggested to be regulated by the transport and initial phosphorylating steps.