Molecular Mechanism Associated With the Impact of Methane/Oxygen Gas Supply Ratios on Cell Growth of 5GB1 Through RNA-Seq.

The methane (CH)/oxygen (O) gas supply ratios significantly affect the cell growth and metabolic pathways of aerobic obligate methanotrophs. However, few studies have explored the CH/O ratios of the inlet gas, especially for the CH concentrations within the explosion range (5∼15% of CH in air). This study thoroughly investigated the molecular mechanisms associated with the impact of different CH/O ratios on cell growth of a model type I methanotroph 5GB1 cultured at five different CH/O supply molar ratios from 0.28 to 5.24, corresponding to CH content in gas mixture from 5% to 50%, using RNA-Seq transcriptomics approach. In the batch cultivation, the highest growth rate of 0.287 h was achieved when the CH/O supply molar ratio was 0.93 (15% CH in air), and it is crucial to keep the availability of carbon and oxygen levels balanced for optimal growth. At this ratio, genes related to methane metabolism, phosphate uptake system, and nitrogen fixation were significantly upregulated. The results indicated that the optimal CH/O ratio prompted cell growth by increasing genes involved in metabolic pathways of carbon, nitrogen and phosphate utilization in 5GB1. Our findings provided an effective gas supply strategy for methanotrophs, which could enhance the production of key intermediates and enzymes to improve the performance of bioconversion processes using CH as the only carbon and energy source. This research also helps identify genes associated with the optimal CH/O ratio for balancing energy metabolism and carbon flux, which could be candidate targets for future metabolic engineering practice.