Microbial protein and lipid production from biogas and syngas using extremophilic methanotroph Methylacidiphilum fumariolicum Pic.

Verrucomicrobial methane-oxidizing bacteria have a broad metabolic versatility, allowing them to utilize a wide range of gaseous feedstocks, highlighting their potential as robust biocatalysts for the valorization of process gases in gas-based biorefineries. In this study, the extremophilic bacteria Methylacidiphilum fumariolicum Pic was cultivated using synthetic biogas, H2 supplemented biogas, and syngas for the production of microbial protein and lipids. Growth based on simultaneous utilization of CH4 and H2 enhanced microbial biomass production, reaching biomass production yield of 1.49 ± 0.11 gdry weight/gcarbon consumed, twice that obtained with biogas. Growth was also sustained on syngas with CO removal rates of 5.0 ± 0.9 mgCO·L-1h-1, although CO inhibition reduced biomass productivity. Proteins represented the major biomass fraction, ranging from 0.43 to 0.63 gprotein/gdry weight. The high protein content and well-balanced amino acid composition indicate potential suitability for aquafeed applications. Lipids accounted for 0.13 to 0.34 glipid/gdry weight and were predominantly composed of branched-chain fatty acids (58-68 % of total fatty acids). Overall, these findings expand the opportunities for utilizing extremophilic methane-oxidizing bacteria in gas-based biorefineries aimed at microbial protein production and its potential valorization as an aquafeed ingredient.