Influences of cultural medium component on the production of poly(γ-glutamic acid) by Bacillus sp. RKY3

Abstract

In this study, the cultural medium used for the efficient production of γ-PGA with a newly isolated Bacillus sp. RKY3 was optimized. It was necessary to supplement the culture medium with L-glutamic acid and an additional carbon source in order to induce the effective production of γ-PGA. The amount of γ-PGA increased with the addition of L-glutamic acid to the medium. The addition of 90 g/L L-glutamic acid to the medium resulted in the maximal yield of γ-PGA (83.2 g/L). The optimum nitrogen source was determined to be peptone, but corn steep liquor, a cheap nutrient, was also found to be effective for γ-PGA production. Both the γ-PGA production and cell growth increased rapidly with the addition of small amounts of K2HPO4 and MgSO4·7H2O. Bacillus sp. RKY3 appears to require Mg2+, rather than Mn2+, for γ-PGA production, which is distinct from the production protocols associated with other, previously reported bacteria. Bacillus sp. RKY3 may also have contributed some minor γ-PGA depolymerase activity, resulting in the reduction of the molecular weight of the produced γ-PGA at the end of fermentation.