biostudies-literatureHe COcean Negative Carbon EmissionsNational Science Foundation of the United States of AmericaNational Natural Science Foundation of Chinawraf049https://www.ebi.ac.uk/biostudies/studies/S-EPMC11994032biostudies-literatureUnknown19(1)SAR202 bacteria are a diverse group of bacteria in the ocean. The SAR202 lineages dominate the bacterial community and evolve specialized metabolisms for oxidizing recalcitrant organic compounds in the dark ocean. SAR202 bacteria are also present in the euphotic oceans; however, their ecological roles and metabolic potential remain poorly understood. In this study, we collected 392 non-redundant metagenome-assembled genomes from different oceans, with 18% of these SAR202 genomes characterized by small genome sizes (<2 Mbp), low GC content (<40%), and high gene density. The 70 genome-streamlined SAR202 bacteria constitute more than an average of 90% of SAR202 in the euphotic zone and exhibit streamlined metabolic features compared to the dark ocean SAR202. Genome-streamlined SAR202 is distrThe ISME journalGenome-streamlined SAR202 bacteria are widely present and active in the euphotic ocean.PMC1199403242188102#182988842141003Jiao NHe CLiu JChen FGonsior MfalseGenome-streamlined SAR202 bacteria are widely present and active in the euphotic ocean.SAR202 bacteria are a diverse group of bacteria in the ocean. The SAR202 lineages dominate the bacterial community and evolve specialized metabolisms for oxidizing recalcitrant organic compounds in the dark ocean. SAR202 bacteria are also present in the euphotic oceans; however, their ecological roles and metabolic potential remain poorly understood. In this study, we collected 392 non-redundant metagenome-assembled genomes from different oceans, with 18% of these SAR202 genomes characterized by small genome sizes (<2 Mbp), low GC content (<40%), and high gene density. The 70 genome-streamlined SAR202 bacteria constitute more than an average of 90% of SAR202 in the euphotic zone and exhibit streamlined metabolic features compared to the dark ocean SAR202. Genome-streamlined SAR202 is distr2025-01-01T00:00:00Z2025 Jan2026-06-02T04:30:10.027Z2025-07-13T03:04:14.121ZS-EPMC119940324019774210.1093/ismejo/wraf049