Improvement of Bacillus subtilis for poly‐γ‐glutamic acid production by genome shuffling

Poly‐γ‐glutamic acid (γ‐PGA) is a promising microbial polymer with potential applications in industry, agriculture and medicine. The use of high γ‐PGA‐producing strains is an effective approach to improve productivity of γ‐PGA. In this study, we developed a mutant, F3‐178, from Bacillus subtilis GXA‐28 using genome shuffling. The morphological characteristics of F3‐178 and GXA‐28 were not identical. Compared with GXA‐28 (18.4 ± 0.8 g l(−1)), the yield of γ‐PGA was 1.9‐fold higher in F3‐178 (34.3 ± 1.2 g l(−1)). Results from batch fermentation in 3.7 l fermenter showed that F3‐178 was satisfactory for industrial production of γ‐PGA. Metabolic studies suggested that the higher γ‐PGA yield in F3‐178 could be attributed to increased intracellular flux and uptake of extracellular glutamate. Real‐time PCR indicated that mRNA level of pgsB in F3‐178 was 18.8‐fold higher than in GXA‐28, suggesting the higher yield might be related to the overexpression of genes involved in γ‐PGA production. This study demonstrated that genome shuffling can be used for rapid improvement of γ‐PGA strains, and the possible mechanism for the improved phenotype was also explored at the metabolic and transcriptional levels.