SAR11 Genome Atlas: a genome and gene catalog for functional profiling of the most abundant bacterial clade in the ocean

The SAR11 clade, also known as the order Candidatus Pelagibacterales, is among the most abundant bacterial lineages in the ocean and plays central roles in marine biogeochemical cycles. However, many SAR11 genes remain functionally uncharacterized, highlighting the need for a comprehensive, integrated catalog that supports genomic, functional, and ecological analyses across the clade. Here, we present the SAR11 Genome Atlas, an interactive ortholog group (OG)-centered web resource that integrates 542 SAR11 genomes, including all 132 cultured strain genomes, with functional annotations, synteny, phylogenetic distribution, metatranscriptomic expression, and predicted protein structure information. To demonstrate its utility, we used environmental expression profiles to identify OGs associated with high-latitude environments, recovering OGs known to be involved in cold adaptation and proposing a hypothesis for the function of uncharacterized protein. We further analyzed phylogenetic distribution patterns to identify mutually exclusive functional modules, including candidate alternative systems for Mn/Zn homeostasis and phosphate acquisition, and to associate these modules with distinct oceanographic environments. Together, these case studies demonstrate that the SAR11 Genome Atlas supports complementary analyses that connect environmental signals to genes of interest and use phylogenetic or functional distributions to generate hypotheses about ecological specialization. Through a user-friendly web interface, the SAR11 Genome Atlas enables researchers to explore genomic, environmental, and structural information without specialized computational expertise. All data and analysis outputs are freely accessible online at [https://stsnsn.github.io/SAR11_Atlas/]. The SAR11 Genome Atlas thus provides a scalable framework for generating and testing hypotheses that connect SAR11 genomic variation to protein function and oceanographic context, supporting advances in marine microbial ecology and biogeochemistry.