A new strategy to enhance polysialic acid production by controlling sorbitol concentration in cultivation of Escherichia coli K235
Polysialic acid (PSA) is a new pharmaceutical material used in control release of protein drugs and as scaffold material in biomedical applications. It is also a vital source of sialic acid and its derivatives. In this paper, we demonstrated that the substrate sorbitol has significant effect on bacterial growth and PSA formation in cultivation of Escherichia coli K235. Lower sorbitol concentration favored bacterial growth but retards PSA formation in the fed-batch fermentation. Higher sorbitol concentration stimulated PSA formation but inhibited bacterial growth in the batch fermentation. Sorbitol concentration gradient experiment revealed that PSA formation was seriously limited as sorbitol concentration was lower than 20 g/L, while bacterial growth was obviously inhibited as the sorbitol concentration higher than 40 g/L. A new strategy of controling sorbitol concentration in a range of 20 - 40 g/L in the broth during the fermentation process increased PSA yield by 20%.