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Enhanced synthesis of poly gamma glutamic acid by increasing the intracellular reactive oxygen species in the Bacillus licheniformis Δ1-pyrroline-5-carboxylate dehydrogenase gene ycgN-deficient strain
- Li, Bichan, Cai, Dongbo, Hu, Shiying, Zhu, Anting, He, Zhili, Chen, Shouwen
- Applied microbiology and biotechnology 2018 v.102 no.23 pp. 10127-10137
- Bacillus licheniformis, acetylcysteine, enzymes, genes, glutamic acid, homeostasis, metabolism, mutants, polyamides, polyglutamic acid, proline, reactive oxygen species
- Poly gamma glutamic acid (γ-PGA) is an anionic polyamide with numerous applications. Previous studies revealed that L-proline metabolism is implicated in a wide range of cellular processes by increasing intercellular reactive oxygen species (ROS) generation. However, the relationship between L-proline metabolism and γ-PGA synthesis has not yet been analyzed. In this study, our results confirmed that deletion of Δ1-pyrroline-5-carboxylate dehydrogenase gene ycgN in Bacillus licheniformis WX-02 increased γ-PGA yield to 13.91 g L⁻¹, 85.22% higher than that of the wild type (7.51 g L⁻¹). However, deletion of proline dehydrogenase gene ycgM had no effect on γ-PGA synthesis. Furthermore, a 2.92-fold higher P5C content (19.24 μmol gDCW⁻¹) was detected in the ycgN deficient strain WXΔycgN, while the P5C levels of WXΔycgM and the double mutant strain WXΔycgMN showed no difference, compared to WX-02. Moreover, the ROS level of WXΔycgN was increased by 1.18-fold, and addition of n-acetylcysteine (antioxidant) decreased its ROS level, which further reduced γ-PGA synthesis capability of WXΔycgN. Collectively, our results demonstrated that proline catabolism played an important role in maintaining ROS homeostasis, and deletion of ycgN-enhanced P5C accumulation, which induced a transient ROS signal to promote γ-PGA synthesis in B. licheniformis.