Prospective bioconversion of CO2 and CO into fine chemicals via halophilic purple phototrophic bacteria

Abstract

Microbial conversion of cheap and problematic carbon sources, like CO₂ and CO, into fine chemicals offers a promising green alternative to numerous traditionally fossil fuel-based industries such as steel, cement, and pharmaceuticals production. Purple phototrophic bacteria (PPB) are emerging as versatile key players in carbon–neutral systems due to their anoxygenic photosynthesis and diverse metabolic capabilities, enabling the transformation of carbon and nutrients into a wide range of valuable products. Traditionally positioned to treat organic carbon and produce medium-value products like bioplastics and biomass, PPB also exhibit autotrophic capabilities, enabling the valorization of waste gases, such as CO₂ and CO. A key strength of PPB is their metabolic and ecological diversity, including species inhabiting saline environments. Halophilic bacteria are known producers of valuable chemicals for pharmaceutical and medical applications, such as osmolytes (ectoine, hydroxyectoine), pigments, amino acids (proline) and natural coenzymes (ubiquinone), yet halophilic PPB remain underexplored in green upcycling processes. This study identified halophilic PPB capable of transforming waste gases into health and wellness products. Through a comprehensive literature review, we compiled a list of halophilic PPB and mined their genomes for genes linked to CO₂/CO utilization as carbon sources. Further genomic search revealed genes encoding enzymes for ectoine/hydroxyectoine, proline, ubiquinone, and carotenoids (lycopene, β-carotene, spirilloxanthin, and spheroidene). We identified 276 genomes of PPB with the genomic potential to valorise CO₂/CO into health-promoting ingredients, highlighting 22 species capable of producing three or more chemicals simultaneously. These findings highlight the untapped potential of halophilic PPB as bio-platforms for sustainable pharmaceutical production.

Graphical abstract