Regulatory mechanisms of CH4 : air volume ratios on metabolic flux partitioning in methane-oxidizing bacteria and their impact on single cell protein biosynthetic efficiency

The results reveal oxygen's critical dual role: higher O₂ levels enhance methane oxidation by activating the copper-dependent catalytic site of pMMO but simultaneously and irreversibly damage the oxygen-sensitive nitrogenase ssential for N₂ fixation, suppressing its activity. Conversely, lower O₂ protects nitrogenase but limits pMMO efficiency. This creates a fundamental metabolic trade-off where the optimal CH₄/O₂ ratio balances these opposing effects, strategically partitioning cellular energy either toward efficient methane assimilation (favored by higher O₂) or toward the ATP-intensive process of nitrogen fixation (requiring lower O₂). These identified gas-ratio thresholds provide actionable parameters for designing scaled SCP bioproduction systems, enabling effective coupling of industrial methane mitigation with sustainable protein synthesis through gas-phase engineering.