Effects of oxygen vectors on the synthesis and molecular weight of poly(γ-glutamic acid) and the metabolic characterization of Bacillus subtilis NX-2

Abstract The effects of different oxygen vectors on the synthesis and molecular weight of poly( γ -glutamic acid) (PGA) were investigated in the batch fermentation of Bacillus subtilis NX-2. n -Hexane, n -heptane, and n -hexadecane enhanced the PGA concentration and molecular weight. The PGA concentration reached a maximum of 39.4 ± 0.19 g L −1 , and the highest molecular weight obtained was (19.0 ± 0.02) × 10 5  Da with the addition of 0.3% n -heptane. However, n -dodecane decreased the PGA concentration and molecular weight to final values of 20.1 ± 0.10 g L −1 and (8.4 ± 0.02) × 10 5  Da, respectively. Analysis of the intracellular nucleotide levels of B. subtilis NX-2 with n -heptane and n -dodecane additives showed that the lowest NADH/NAD + ratio and ATP levels were obtained with the n -dodecane additives, which can explain the decreased PGA yield and molecular weight. The metabolic flux distribution of B. subtilis NX-2 with n -heptane and n -dodecane additives was also investigated. Flux distribution was primarily directed to the EMP and TCA cycles with n -heptane additives. The flux of 2-oxoglutarate to intracellular glutamate and the flux distribution from extracellular to intracellular glutamate both increased to improve PGA production.