Improvement of poly(γ-glutamic acid) biosynthesis and redistribution of metabolic flux with the presence of different additives in Bacillus subtilis CGMCC 0833

Tween-80, dimethyl sulfoxide (DMSO), and glycerol could be used as novel materials to regulate the central carbon metabolic pathway and improve γ-PGA biosynthesis by Bacillus subtilis CGMCC 0833. With glycerol in the medium, the activity of 2-oxoglutarate dehydrogenase complex at the key node of 2-oxoglutarate was depressed, more carbon flux distribution was directed to synthesize glutamate, the substrate of γ-PGA, which led to overproducing of γ-PGA, reached 31.7 g/l, compared to the original value of 26.7 g/l. When Tween-80 or DMSO was in the medium, the activity of isocitrate dehydrogenase was stimulated, the branch flux from 2-oxoglutarate to glutamate was also enhanced due to the increasing of total flux from iso-citrate to 2-oxoglutarate, then a large amount of glutamate was produced, and formation of γ-PGA was also improved, which was a different process compared with that of glycerol. Moreover, with the addition of Tween-80 or DMSO, cell membrane permeability was increased, which facilitated the uptake of extracellular substrates and the secretion of γ-PGA by this strain; therefore, γ-PGA production was further stimulated, and 34.4 and 32.7 g/l γ-PGA were obtained, respectively. This work firstly employed additives to improve the biosynthesis of γ-PGA and would be helpful in understanding the biosynthesis mechanism of γ-PGA by Bacillus species deeply.