Uncoupling of growth and exopolysaccharide production by Lactococcus lactis subsp. cremoris NIZO B40 and optimization of its synthesis

Abstract

Exopolysaccharide (EPS) production by Lactococcus lactis subsp. cremoris NIZO B40 was found to be most efficient with glucose as a substrate. The optimal temperature and pH for EPS synthesis were 25°C and pH 5.8, respectively. EPS production could not be identified as a stress response: increased oxygen tension and reduced water activity negatively affected both growth and EPS synthesis. It is often assumed that there is a competition between growth and EPS formation. Within the range of 0.5 and 0.1 h −1, reducing the growth rate resulted indeed in an increase of the specific EPS production but the polymer formation decreased again at even lower growth rates. Most of the applied fermentation conditions influenced both growth and EPS formation. As the growth rate itself also influenced EPS formation, we studied the linking between growth and EPS synthesis. Interestingly, EPS production was not strictly coupled to growth. Significant de novo synthesis of EPS was observed in non-growing cultures. Consequently, the influence of different culture conditions on EPS production could be studied independent of growth.