Forces Shaping Diversity of Hydrogen Peroxide Detoxification Potential in Ocean Microbial Ecosystems

ABSTRACT Microbial communities have evolved interactions to support growth and essential ecosystem functions. For example, marine cyanobacteria like Prochlorococcus lack the catalase genes ( katE , katG and manganese catalase ) required for detoxifying freely‐diffusible hydrogen peroxide, relying on co‐occurring catalase‐carrying ‘helper’ microbes for this function. However, the eco‐evolutionary forces shaping catalase distribution are not well understood. We examined genomes, metagenome‐assembled genomes (MAGs), and metagenomes to assess catalase gene distributions across diverse marine prokaryotes—including within the known ‘helper’ genus Alteromonas —and across surface ocean ecosystems. Within Alteromonas , most genomes contain two katE copies, while katG copy number varies across species. Across ecosystems, the Altermonadaceae family is the predominant katE carrier. Some taxa (e.g. , SAR202) lack all catalases, highlighting their dependence on ‘helpers’. Overall, streamlined genomes, including from SAR11, generally have one katG copy and lack katE , while larger genomes with higher GC content characteristic of copiotrophs have more copies of both catalases. Finally, in free‐living communities, katG gene frequency increases with decreased particulate organic carbon (POC) concentrations, whereas in particle‐associated communities , katE gene frequency increases with elevated POC. Together, these observations suggest that hydrogen peroxide detoxification capabilities are widespread and shaped by the contributions of particle‐associated microbes to total community metabolism.