'Candidatus Viridifilum namsaraevi' gen. nov., sp. nov., a new mesophilic filamentous anoxygenic phototrophic bacterium from the mesothermal lake Umkhey (Buryatia).

A novel mesophilic filamentous phototrophic bacterium from Lake Umkhey's microbial mats has a complete 3-hydroxypropionate bicycle for CO₂ fixation and occupies an intermediate phylogenetic position within Chloroflexota.

• Why it matters: Understanding the evolution of phototrophy and carbon fixation in Chloroflexota is limited by the scarcity of cultured mesophilic representatives, hindering insights into metabolic and evolutionary transitions in this group.
• What they did: Researchers recovered the genome of 'Candidatus Viridifilum namsaraevi' from environmental samples using metagenome-assembled genome reconstruction, enabling detailed phylogenomic and metabolic analysis of this new lineage.
• The result: This discovery provides new insights into photosynthetic and carbon-fixation pathway evolution, and offers a genomic reference for studying metabolic adaptation in alkaline, sulfide-rich microbial mats.