Optimization and Characterization of Poly-γ-Glutamic Acid Production From a Locally Isolated Bacillus cereus ARM24

For identification of this new local poly-γ-glutamic acid (γ-PGA) bacteria and partial purification of γ-PGA, the bacterium was studied and identified as Bacillus cereus. Sixty isolates of Bacillus spp. were collected from 28 sources (agricultural soil, local market vegetables, and fruits). Preliminary screening was performed on selective plates; 37 strains were selected on the basis of their ability to form a slimy mucoid colony. All isolates were studied for morphological and microscopic characters and identified by biochemical tests; a test for the production of γ-PGA was conducted with spectrophotometric determination of the polymer concentration at 216 nm. The best local strain B3, causing 2.54 g/mL of polymer, was chosen. Isolated strain was designated ARM24 and was published elsewhere with 99% identity as B. cereus ARM24 under the GenBank accession number. Optimization studies indicated that the optimum conditions for γ-PGA production were 37°C, pH 7, inoculum size 2 mL, shaking speed 200 rpm, and fermentation time 48 h using grape pomace juice as carbon source and soybean meal with salting out as nitrogen source. The polymer was precipitated from cold 99% ethanol with a recovery rate of 3:1, purified by dialysis bags (10,000 Da), and characterized by Fourier transform infrared (FT-IR), thin-layer chromatography (TLC), ¹H-NMR, and high-performance liquid chromatography (HPLC).