Production of ε-poly-l-lysine using a novel two-stage pH control strategy by Streptomyces sp. M-Z18 from glycerol

The production of epsilon-poly-l-lysine (epsilon-PL) by Streptomyces sp. M-Z18 from glycerol was investigated in a 5-L jar-fermenter. Batch fermentations by Streptomyces sp. M-Z18 at various pH values ranging from 3.5 to 4.5 were studied. Based on the analysis of the time course of specific cell growth rate and specific epsilon-PL formation rate, a novel two-stage pH control strategy was developed to improve epsilon-PL production by shifting the culture pH from 3.5 to 3.8 after 36 h of cultivation. By applying the strategy, the maximal epsilon-PL concentration and productivity had a significant improvement and reached 9.13 g L(-1) and 4.76 g L(-1) day(-1), respectively, compared with those in one-stage pH control process where the pH value is controlled at 3.5 (7.83 g L(-1) and 3.13 g L(-1) day(-1)). Fed-batch fermentation with two-stage pH control strategy was also applied to produce epsilon-PL; final epsilon-PL concentration of 30.11 g L(-1) was obtained, being 3.3-fold greater than that of batch fermentation. To our knowledge, it is the first report on production of epsilon-PL from glycerol in fermenter scale and achievement of high epsilon-PL production with two-stage pH control strategy.