A novel glutamate transport system in poly(γ-glutamic acid)-producing strain Bacillus subtilis CGMCC 0833

Optimization of γ-polyglutamic acid synthesis using response surface methodology of a newly isolated glutamate dependent Bacillus velezensis Z3

A new glutamate-dependent γ-polyglutamic acid (γ-PGA) producer Z3 isolated from soil samples in Daxinganling forest region of China was identified, and its optimal medium components were investigated using response surface methodology. Strain Z3 was identified as Bacillus velezensis by physiology and biochemistry and 16S rDNA sequence analysis. This is the first report of glutamate-dependent B. velezensis with the ability to synthesize γ-PGA. Then, the optimum γ-PGA yield (5.58 g/L) was achieved with glutamate 86 g/L, glucose 36 g/L, yeast extract powder 5.5 g/L, and NaH₂PO₄ 7.5 g/L. Furthermore, activities of enzymes participating in glutamate synthesis were assessed, and the results showed that lower ketoglutaric dehydrogenase activity (KGDH) and higher glutamate dehydrogenase activity (GDH) resulted in higher γ-PGA yield. Identification of glutamate-dependent γ-PGA producer named B. velezensis Z3 enriches microbiological resources with γ-PGA-producing capacity. B. velezensis optimization of nutrients and analysis of enzymes activities will not only help to increase γ-PGA productivity but also to understand the γ-PGA synthesis mechanism in B. velezensis Z3.

Production of poly-γ-glutamic acid by a thermotolerant glutamate-independent strain and comparative analysis of the glutamate dependent difference

Poly-γ-glutamic acid (γ-PGA) is a promising microbial polymer with wide applications in industry, agriculture and medicine. In this study, a novel glutamate-independent γ-PGA producing strain with thermotolerant characteristics was isolated and identified as Bacillus subtilis GXG-5, then its product was also characterized. The fermentation process was optimized by single-factor tests, and results showed that high temperature (50 °C) was especially suitable for the γ-PGA production by GXG-5. The γ-PGA yield reached 19.50 ± 0.75 g/L with substrate conversion efficiency of 78% at 50 °C in 10 L fermentor. Comparison of GXG-5 and GXA-28 (glutamate-dependent strain) under respective optimal fermentation conditions, the γ-PGA yield of GXG-5 was 19.0% higher than that of GXA-28, and GXG-5 was also superior to GXA-28 in the availability of carbon sources and substrates. Furthermore, the glutamate dependent difference between GXA-28 and GXG-5 was analyzed by genomic sequencing, results indicated that genes related to the glutamate dependent difference mainly involved in carbohydrate transport and metabolism and amino acid metabolism, and 13 genes related to γ-PGA synthesis were mutated in GXG-5. This study provided a potential glutamate-independent strain to replace glutamate-dependent strain for γ-PGA production, and shared novel information for understanding the glutamate dependent difference at the genomic level.