The statistically optimized production of poly(γ-glutamic acid) by batch fermentation of a newly isolated Bacillus subtilis RKY3

For the production of poly(γ-glutamic acid), a newly isolated Bacillus sp. RKY3 was phylogenetically identified as Bacillus subtilis based on its 16S rRNA gene sequence. The culture medium for the production of poly(γ-glutamic acid) by B. subtilis RKY3 was optimized statistically. The parameters significantly affecting poly(γ-glutamic acid) production were found to be glycerol, glutamic acid, yeast extract, and K2HPO4. A further advanced statistical approach, central composite design, found the optimum levels of the screened variables as follows (g l−1): glycerol 17.6, glutamic acid 59.6; yeast extract 2.7; K2HPO4 2.3. The predicted response as poly(γ-glutamic acid) production under the statistically optimized conditions was 48.5 g l−1, which was only 0.4% different from the maximum poly(γ-glutamic acid) concentration (48.7 g l−1) observed at the validation experiment using 7-l lab-scale fermentor containing 3 l of working volume.