Enhancement of polysialic acid yield by reducing initial phosphate and feeding ammonia water to Escherichia coli CCTCC M208088

Polysialic acid (PSA) is a capsular polysaccharide obtained from aerobic fermentation with Escherichia coli. To enhance PSA production and eliminate the influence of phosphate on the PSA purification process, a lower level of initial phosphate was adopted with pH control. The resulting PSA yield reached 4.1 g/L in fed-batch fermentation with 2.5 g/L K2HPO4 and E. coli strain CCTCC M208088. In addition, an ammonia water (NH4OH) feeding strategy to control the pH at 6.4 was developed resulting in PSA production that reached as high as 5.2 g/L. NMR spectra confirmed the purified biopolymer as a α-2,8 linked PSA, identical to the published NMR spectra, with a molecular weight in the range of 16 ∼ 50 kDa.