Multi-production of high added market value metabolites from diluted methane emissions via methanotrophic extremophiles

This study constitutes the first-proof-of-concept of a methane biorefinery based on the multi-production of high profit margin substances (ectoine, hydroxyectoine, polyhydroxyalkanoates (PHAs) and exopolysaccharides (EPS)) using methane as the sole carbon and energy source. Two bubble column bioreactors were operated under different magnesium concentrations (0.2, 0.02 and 0.002 g L⁻¹) to validate and optimize this innovative strategy for valorization of CH₄ emissions. High Mg²⁺ concentrations promoted the accumulation of ectoine (79.7–94.2 mg g biomass⁻¹), together with high hydroxyectoine yields (up to 13 mg g biomass⁻¹) and EPS concentrations (up to 2.6 g L culture broth⁻¹). Unfortunately, PHA synthesis was almost negligible (14.3 mg L⁻¹) and only found at the lowest Mg²⁺ concentration tested. Halomonas, Marinobacter, Methylophaga and Methylomicrobium, previously described as ectoine producers, were dominant in both bioreactors, Methylomicrobium being the only described methanotroph. This study encourages further research on CH₄ biorefineries capable of creating value out of GHG mitigation.