Abstract

A newly isolated poly-(γ-glutamic acid) (γ-PGA)-producing strain BABRC-11 was identified as Bacillus subtilis based on its morphological and physiological characteristics as well as 16S rDNA sequence. The fermentation medium for the production of γ-PGA by B. subtilisBABRC-11 was optimized statistically. The parameters significantly affecting γ-PGA production were found to be sodium glutamate, calcium chloride (CaCl₂) and zinc chloride (ZnCl₂) by Plackett–Burman design, but ZnCl₂ was a negatively significant factor. A further advanced statistical approach, central composite design, found the optimum levels of the screened variables as follows: sodium glutamate 18.74 g/L; CaCl₂ 0.17 g/L. After 48-h fermentation, 13.67 g/L of γ-PGA was produced under the optimum condition with only 0.1% differences from the statistically predicted value (13.69 g/L).

Key words: Poly (γ-glutamic acid), Bacillus subtilis, Plackett–Burman design, central composite design.