Optimization of carbon and nitrogen sources and substrate feeding strategy to increase the cell density of Streptococcus suis

Abstract

The swine pathogen Streptococcus suis is a worldwide emerging threat to public health. Efforts to develop an effective vaccine require the economic production of sufficient quantities of bacteria. To address this issue, the goal of the present study was to optimize culture conditions by reducing the accumulation of lactate through optimization of the medium components and feeding strategy. Sucrose (5 g/L) and a mixture of yeast extract and peptone (4 g/L each) were the most effective carbon and nitrogen sources, respectively, for S. suis ST171 fermentation. Further, from the results of S. suis ST171 fermentation with different ratios of carbon/nitrogen, 2 g/L sucrose was used as a carbon source and a mixture of 4 g/L yeast extract and 4 g/L peptone was used as a nitrogen source. Using these optimized conditions, S. suis ST171 fermentation with glucose-stat feeding strategy cultures accumulated a low concentration of lactate (3.47 g/L), which was accompanied by a high cell yield (2.712) and viability (1.192 × 1010 colony forming units/mL).