High-level production of poly-γ-glutamic acid from untreated molasses by Bacillus siamensis IR10

Background Poly-gamma-glutamic acid (gamma-PGA) is a promising biopolymer and has been applied in many fields. Bacillus siamensis SB1001 was a newly isolated poly-gamma-glutamic acid producer with sucrose as its optimal carbon source. To improve the utilization of carbon source, and then molasses can be effectively used for gamma-PGA production, (60)cobalt gamma rays was used to mutate the genes of B. siamensis SB1001. Results Bacillus siamensis IR10 was screened for the production of gamma-PGA from untreated molasses. In batch fermentation, 17.86 +/- 0.97 g/L gamma-PGA was obtained after 15 h, which is 52.51% higher than that of its parent strain. Fed-batch fermentation was performed to further improve the yield of gamma-PGA with untreated molasses, yielding 41.40 +/- 2.01 g/L of gamma-PGA with a productivity of 1.73 +/- 0.08 g/L/h. An average gamma-PGA productivity of 1.85 g/L/h was achieved in the repeated fed-batch fermentation. This is the first report of such a high gamma-PGA productivity. The analysis of the enzyme activities showed that they were affected by the carbon sources, enhanced ICDH and GDH, and decreased ODHC, which are important for gamma-PGA production. Conclusion These results suggest that untreated molasses can be used for economical and industrial-scale production of gamma-PGA by B. siamensis IR10.