Production of ultra‐high‐molecular‐weight poly‐γ‐glutamic acid by a newly isolated Bacillus subtilis strain and genomic and transcriptomic analyses

Abstract

Poly‐γ‐glutamic acid (γ‐PGA) is a microbial‐derived polymer with molecular weight (Mw) from 104 to 107 Da, and the high‐Mw (> 7.0 × 105 Da) or ultra‐high‐Mw (> 5.0 × 106 Da) γ‐PGA has important application value as a tissue engineering material, as a flocculant, and as a heavy metal remover. Therefore, how to produce these high‐Mw γ‐PGAs with low cost and high efficiency has attracted wide attention. In this study, a γ‐PGA producer was isolated from the natural environment, and identified and named Bacillus subtilis GXD‐20. Then, the ultra‐high‐Mw (> 6.0 × 106 Da) γ‐PGA produced by GXD‐20 was characterized. Interestingly, GXD‐20 could produce γ‐PGA at 42°C, and exhibited a γ‐PGA titer of up to 22.29 ± 0.59 g L−1 in a 5‐L fermenter after optimization of the fermentation process. Comparative genomic analysis indicated that the specific protein sequence and subcellular localization of PgdS (a γ‐PGA‐degrading enzyme) were closely related to the ultra‐high‐Mw of γ‐PGA. Transcriptomic analysis revealed that the high γ‐PGA titer at 42°C was mainly related to the high expression of genes encoding enzymes for sucrose transportation and utilization, nitrogen transportation, endogenous glutamate synthesis, and γ‐PGA synthesis. These results provide new insights into the production of ultra‐high‐Mw γ‐PGA by Bacillus at high temperatures.