Enhanced growth and microbial protein production of <i>Methylotuvimicrobium alcaliphilum</i> 20Z through process optimization

The halotolerant methanotroph Methylotuvimicrobium alcaliphilum 20Z represents a promising platform for simultaneous methane mitigation and production of value-added metabolites, such as the single-cell protein. This study aimed to determine the optimal CH4/O₂ ratio and concentrations of key supplements [paraffin oil, folic acid (FA), and malic acid] in batch cultures to concurrently enhance biomass and protein yield. Under the optimized conditions (1:4 CH4:air, 2% (v/v) paraffin oil, 10 μg/L FA, and 1 mmol/L malic acid), maximum biomass and protein production reached 4.20 ± 0.19 g/L and 984.90 ± 45.34 mg/L, respectively. Intracellular glycogen content varied substantially between 50 and 800 mg/L. A notable shift in intracellular composition was observed during batch cultivation: rising biomass was associated with declining protein content but increasing glycogen reserves. These findings establish a foundation for rational media formulation and scale-up of M. alcaliphilum 20Z cultivation for industrial protein production.