Optimization of Fed-batch Culture Strategy for Improved Synthesis of Nisin by Lactococcus lactis HB03

Abstract

To improve the efficiency of nisin synthesis by Lactococcus lactis HB03, the oxidative stress effect and the pattern of changes in the concentration of extracellular amino acids during the growth and fermentation of this strain were determined. Then, the differences in gene expression related to the peptide hydrolase system, UMP de novo synthesis, and peptidoglycan anabolism at the transcriptome level were analyzed. As a result, deficiencies of cysteine (Cys) and arginine (Arg) were identified as the limiting factors for nisin synthesis at the mid to late logarithmic phase. The optimal fed-batch culture strategy in a 10 L fermentor was obtained as follows: addition of 0.15 mmol/L Cys at 11, 13.5, 17, and 19.5 h, addition of 15 g/L peptone at 12 h, addition of sucrose at a flow rate of 1.5 g/(L·h) during 10 to 24 h, and addition of Arg at a flow rate of 0.25 g/(L·h) during 12 to 21 h. Under these conditions, nisin production was increased to 8 963 IU/mL, which was 28.2% higher than that obtained by adding only Cys (6 993 IU/mL). These results provide an important reference for the industrial fermentation of nisin.

Keywords

• lactococcus lactis; nisin; fed-batch culture optimization; fermentative synthesis