Production and optimization of poly-γ-glutamic acid by Bacillus subtilis BL53 isolated from the Amazonian environment

The aims of this research were to screen and characterize a new microbial source of γ-PGA, to optimize aspects of culture conditions and medium composition using central composite design and response surface methodologies. The influence of bioreactor stirring rates on the production of γ-PGA was also investigated and the oxygen volumetric mass transfer coefficients (k La) were established. The most productive strain was identified by 16S rDNA analysis as Bacillus subtilis, and its γ-PGA production in rotatory shaker was threefold increased under optimized conditions (37 °C, pH 6.9, and 1.22 mM Zn(2+)), compared to conventional medium. In bioreactor, the γ-PGA production was further increased, reaching 17 g l(-1), 70 % higher than shaker cultures. γ-PGA production showed high dependency on oxygen transfer. At k La of 210 h(-1), the cultivation time could be reduced to 48 h, about 50 % of the time required for operations at k La 55 h(-1).