Abstract
PurposeTo explore a competitive PHB-producing fermentation process, this study evaluated the potential for Methylobacterium sp. XJLW to produce simultaneously PHB and coenzyme Q10 (CoQ10) using methanol as sole carbon and energy source.MethodsThe metabolic pathways of PHB and CoQ10 biosynthesis in Methylobacterium sp. XJLW 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 CoQ10, respectively. PHB and CoQ10 productivity of Methylobacterium sp. XJLW were evaluated in Erlenmeyer flask for medium optimization, and in a 5-L bioreactor for methanol fed-batch strategy according to dissolved oxygen (DO) and pH control.ResultsComparative genomics analysis showed that the PHB and CoQ10 biosynthesis pathways co-exist in Methylobacterium sp. XJLW. Transcriptomics analysis showed that the transcription level of key genes in both pathways responding to methanol was significantly higher than that responding to glucose. Correspondingly, strain Methylobacterium sp. XJLW can produce PHB and CoQ10 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 CoQ10. The optimal medium and cultural conditions for PHB and CoQ10 co-production by Methylobacterium sp. XJLW was in M3 medium containing 7.918 g L-1 methanol, 0.5 g L-1 of ammonium sulfate, 0.1% (v/v) of Tween 80, and 1.0 g L-1 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-1) with the highest yields of PHB and CoQ10, reaching 6.94 g L-1 and 22.28 mg L-1, respectively.ConclusionMethylobacterium sp. XJLW is potential for efficiently co-producing PHB and CoQ10 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 CoQ10 simultaneously by Methylobacterium sp. XJLW. It also suggests a potential strategy to develop efficiently co-producing other high-value metabolites using methanol-based bioprocess.
Highlights
Nowadays, along with the increasing demands for polymer plastics, which can be widely used from product packing and daily tools to equipment parts and construction sectors, the growing serious petroleum-based plastic pollution has drawn more attractive attention due to its less biodegradation property (Cardoso et al 2020; Mostafa et al 2020)
Carbon source is regarded as the major factor that accounts for 70–80% of the total expenses of PHAs (Mohandas et al 2017), because PHAs are usually synthesized under a specific condition of limitation of nutrients, and excess of carbon source (Cardoso et al 2020)
XJLW was identified via gas chromatography/mass spectrometry (GC-MS), nuclear magnetic resonance (NMR), and IR analysis methods, respectively
Summary
Along with the increasing demands for polymer plastics, which can be widely used from product packing and daily tools to equipment parts and construction sectors, the growing serious petroleum-based plastic pollution has drawn more attractive attention due to its less biodegradation property (Cardoso et al 2020; Mostafa et al 2020). The high cost of PHA production from costly substrates has seriously limited the utilization of PHAs in commercial fields, which forces scientists to explore alternative approaches to produce it at a lower price (Parveez et al 2015). The production costs of PHAs depend on many factors including strains, substrates, cultivation conditions, extraction, and purification processes (Gamez-Perez et al 2020). Methanol-based fermentation for PHA production is still a highly promising process without sugar consumption
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