Investigating the relationship between the specific glucose uptake rate and nisin production in aerobic batch and fed-batch glucostat cultures of Lactococcus lactis

The relationship between specific glucose uptake rate and nisin production by Lactococcus lactis was investigated in aerobic batch and fed-batch cultures in which glucose was maintained stable during the production phase (glucostat) at levels ranging from 2.5 to 75 g/l. Both initial concentration and the level of glucose the cells experience affected specific nisin production rates. The maximum nisin titer obtained in glucostat cultures was 6100 IU/ml at 10 g/l glucose, a significantly higher amount compared to the maximum titer of 3122 IU/ml in batch culture with 25 g/l initial glucose concentration. At glucose concentration levels exceeding 10 g/l in fed-batch culture, specific nisin production rates were reduced and specific glucose uptake rates data showed that glucose transport inside the cells is saturated. Obviously, the concentration of glucose regulates its uptake and improving its uptake could result in nisin yield improvement. By employing the tool of glucostat fed-batch culture, glucose concentration was effectively controlled at levels ensuring an optimum uptake rate for maximum nisin production.