Metabolomics-assisted mechanism analysis of gamma-PGA synthesis regulated by PhoP in B. licheniformis

Poly {gamma}-glutamic acid ({gamma}-PGA) is a widely used biopolymer whose synthesis relies on external nitrogen sources. PhoP is a global transcription factor that has been reported to be involved in regulation of phosphorus and nitrogen metabolisms, whether PhoP regulates {gamma}-PGA synthesis is worthy of further study. In this study, {gamma}-PGA yield was decreased by 19.4% in phoP deletion strain, while PhoP overexpression benefited {gamma}-PGA synthesis in Bacillus licheniformis, and the results of transcriptional level, electrophoretic mobility shift (EMSA) and GFP expression assays confirmed the direct positive regulation on {gamma}-PGA synthetase gene pgsB by PhoP. Furthermore, based on metabolomic and physiological analysis, we dissected three aspects that {gamma}-PGA synthesis indirectly regulated by PhoP. (i) PhoP influences glutamate transport through positively regulating glutamate transporter GltT. (ii) PhoP influences nitrogen source utilization through negatively regulating nitrogen metabolic repressor TnrA and positively regulating GlnR. (iii) PhoP influences ammonia assimilation through GlnR and TnrA. Together, our study improved metabolic regulatory network of {gamma}-PGA synthesis, and laid a foundation for PhoP regulation nitrogen metabolic network in Bacillus.