Co-production of biopolymers and quinone via no-sugar fermentation--a case by Methylobacterium sp. XJLM
Abstract Purpose To explore a competitive PHB producing fermentation process, this study evaluated the potential for Methylobacterium sp. XJLW to produce simultaneously PHB and coenzyme Q 10 (CoQ 10 ) using cheap and abundant methanol as sole carbon and energy source. Methods The metabolic pathways of PHB and CoQ 10 biosynthesis in XJLW strain were first mined based on the genomic and comparative transcriptomics information. Then, Real-time fluorescence quantitative PCR (RT-qPCR) was employed for comparing the expression level of important genes involved in PHB and CoQ10 synthesis pathways response to methanol and glucose. Transmission electron microscope (TEM), gas chromatography/mass spectrometry (GC-MS), nuclear magnetic resonance (NMR), Fourier transformation infrared spectrum (FT-IR), and liquid chromatography/mass spectrometry (LC-MS) methods, were used to elucidate the yield and structure of PHB and CoQ 10 , respectively. PHB and CoQ 10 productivity of XJLW strain were evaluated in flasks for medium optimization, and in a 5-L bioreactor for methanol fed-batch strategy according to dissolved oxygen (DO) and pH control. Results Comparative genomics and transcriptomics analysis showed that the PHB and CoQ 10 biosynthesis pathways coexist in XJLW strain, and the transcription level of key genes in both pathways response to methanol was significantly higher than that response to glucose. Correspondingly, strain XJLW can produce PHB and CoQ 10 simultaneously with higher yield using cheap and abundant methanol than using glucose as sole carbon and energy source. The isolated products showed the structure characteristics same to that of standard PHB and CoQ 10 . The optimal medium and cultural conditions for PHB and CoQ 10 co-production by XJLW strain was in M3 medium containing 1% (v/v) of methanol, 0.5 g/L of ammonium sulfate, 0.1% (v/v) of Tween 80, and 1.0 g/L of sodium chloride, under 30°C and pH 7.0. In a 5-L bioreactor coupled with methanol fed-batch process, a maximum DCW value (46.31 g/L) with the highest yields of PHB and CoQ 10 , reaching 6.94 g/L and 22.28 mg/L, respectively. Conclusion Methylobacterium sp. XJLW is potential for efficiently co-producing PHB and CoQ 10 employing methanol as sole carbon and energy source. However, it is still necessary to further optimize fermentation process, and genetically modify strain pathway, for enhanced production of PHB and CoQ 10 simultaneously by XJLW. It also suggests a potential strategy to develop efficiently co-producing other high value metabolites using methanol-based bio-process.