Optimization of γ-polyglutamic acid synthesis using response surface methodology of a newly isolated glutamate...

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.