Optimization and Characterization of Poly‐γ‐Glutamic Acid Production From a Locally Isolated <i>Bacillus cereus</i> ARM24

ABSTRACT 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), 1 H‐NMR, and high‐performance liquid chromatography (HPLC).