Isolation, Identification and Evaluation of Egyptian Bacillus sp. Isolates for Producing Poly-γ-glutamic Acid

Abstract

Poly-γ-glutamic acid (γ-PGA) is a non-toxic, biodegradable, and water-soluble polymer secreted from different microbes. We isolated forty-nine Bacillus spp. isolates generating PGA from the soil of different Egyptian regions. A total of 18% of these isolates were found to highly produce PGA in the range of 5- 8 gl-l. Two of them, B44 and B42, were identified by the16SrRNA DNA sequence, and they shared 81% of similarity. The most similar DNA sequences to B44-16SrRNA were Bacillus sp. (FJ607057.1) and Bacillus sonorensis (KP236346.1) matching 99% and 94% of similarity, respectively. However, B42-16SrRNA was similar 99% to several Bacillus species. The tree-building algorithm MEGA-X constructed the phylogenetic tree of 16SrRNA DNA sequences for Bacillus 44 and Bacillus 42 strains along with other similar Bacillus species revealing the distance between them. We also boosted the PGA production of both strains. Bacillus 44 strain revealed the highest accumulation level of PGA at 35°C and 72 h of incubation using medium M with inoculum size and agitation speed 3% and 250 rpm, respectively. Both strains secreted the PGA biopolymer with a molecular mass of 55 kDa. This investigation is an attempt of boosting promising Egyptian Bacillus sp. isolates for PGA production that may be a seed for industrial production.