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

Poly--glutamic acid (-PGA) is a promising microbial polymer with potential applications in industry, agriculture and medicine. The use of high -PGA-producing strains is an effective approach to improve productivity of -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 +/- 0.8gl(-1)), the yield of -PGA was 1.9-fold higher in F3-178 (34.3 +/- 1.2gl(-1)). Results from batch fermentation in 3.7l fermenter showed that F3-178 was satisfactory for industrial production of -PGA. Metabolic studies suggested that the higher -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 -PGA production. This study demonstrated that genome shuffling can be used for rapid improvement of -PGA strains, and the possible mechanism for the improved phenotype was also explored at the metabolic and transcriptional levels.