Genomic Survey of Carbon Monoxide Dehydrogenases Reveals Their Widespread Distribution in Marine Habitats

Most carbon monoxide (CO) produced in the ocean is consumed by microorganisms encoding carbon monoxide dehydrogenases (CODHs), thereby significantly reducing the flux of CO from the ocean to the atmosphere. CODHs are of two types based on the metal content of their active sites: the oxygen‐sensitive, nickel‐containing Ni‐CODH and the oxygen‐tolerant, molybdenum–copper‐containing Mo‐CODH. Although CODHs have been reported from specific marine environments, their combined distribution across ocean ecosystems remains unclear. Here, we analyzed the NCBI non‐redundant protein database and identified 1969 Ni‐CODH and 864 Mo‐CODH genes from marine prokaryotes spanning diverse oceanic ecosystems. Using metagenomic analyses across three marine biomes, we showed that oxygen availability selectively constrains Ni‐CODH gene abundance, but not Mo‐CODHs. Thus, Ni‐CODHs are restricted to oxygen‐limited niches, while Mo‐CODHs occur across both oxygenated and oxygen‐limited marine environments. Phylogenetic analyses indicated that all previously described CODH clades are represented in the marine ecosphere, highlighting their evolutionary diversity. Genome context analyses suggest that approximately 50% of the marine Ni‐CODH potentially participate in carbon fixation via the Wood‐Ljungdahl pathway, whereas most marine Mo‐CODH likely contribute to the supplementary energy conservation. Together, these results provide an integrated view of CODH distribution and potential function in marine ecosystems.