Harnessing Biogas into High-Value Chemicals: The Role of Algal–Methanotrophic Co-Cultures

The conversion of biogas into high-value chemicals for pharmaceutical, cosmetic, and nutraceutical markets offers an attractive alternative to conventional fossil-based production routes, enabling circular value chains with significant socio-economic impact. This study evaluated the valorization of biogas into osmolyte and carotenoid compounds with market prices ranging from 1000 to 7000 $·kg^-1. Specifically, an algal-methanotrophic co-culture operated under saline conditions, preventing external microbial contamination and stimulating osmolytes and carotenoids, was assessed for its capacity to simultaneously remove methane (CH₄) and carbon dioxide (CO₂), with efficiencies of 92 and 89%, respectively. while producing ectoine, hydroxyectoine, lutein, β-carotene, and astaxanthin. Shotgun metagenomic analyses identified the key microorganisms driving the process, predominantly alkaliphilic and halophilic green algae (<i>Chlorella</i>, <i>Dunaliella</i>) and cyanobacteria (<i>Leptolyngbya</i>), and halotolerant methanotrophs (<i>Methylotuvimicrobium</i>) and methylotrophs (<i>Methylophaga</i>). Metagenomics further revealed the presence of key metabolisms related to C1 utilization and biosynthetic genes associated with carotenoid and osmolyte production, confirming the metabolic potential of the consortium to convert biogas-derived carbon directly into high-value compounds. Overall, these results demonstrate the feasibility of an efficient, biologically driven bio-platform capable of transforming greenhouse gas-rich waste streams into economically relevant bioactive molecules, contributing to global priorities in sustainable biomass-to-biochemical innovation.