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 gamma-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 gamma-PGA was also investigated and the oxygen volumetric mass transfer coefficients (k (L)a) were established. The most productive strain was identified by 16S rDNA analysis as Bacillus subtilis, and its gamma-PGA production in rotatory shaker was threefold increased under optimized conditions (37 A degrees C, pH 6.9, and 1.22 mM Zn2+), compared to conventional medium. In bioreactor, the gamma-PGA production was further increased, reaching 17 g l(-1), 70 % higher than shaker cultures. gamma-PGA production showed high dependency on oxygen transfer. At k (L)a of 210 h(-1), the cultivation time could be reduced to 48 h, about 50 % of the time required for operations at k (L)a 55 h(-1).