biostudies-literatureChu Xthe Hong Kong Research Grants Council General Research Fundthe Hong Kong Research Grants Council Area of Excellence Schemethe Direct Grant of CUHKthe Shenzhen Science and Technology Communitythe National Science Foundation of Chinae0057122https://www.ebi.ac.uk/biostudies/studies/S-EPMC9426536biostudies-literatureUnknown13(4)Globally dominant marine bacterioplankton lineages are often limited in metabolic versatility, owing to their extensive genome reductions, and thus cannot take advantage of transient nutrient patches. It is therefore perplexing how the nutrient-poor bulk seawater sustains the pelagic streamlined lineages, each containing numerous populations. Here, we sequenced the genomes of 33 isolates of the recently discovered CHUG lineage (~2.6 Mbp), which have some of the smallest genomes in the globally abundant Roseobacter group (commonly over 4 Mbp). These genome-reduced bacteria were isolated from a transient habitat: seawater surrounding the brown alga, Sargassum hemiphyllum. Population genomic analyses showed that: (i) these isolates, despite sharing identical 16S rRNA genes, were differentiatemBioCoastal Transient Niches Shape the Microdiversity Pattern of a Bacterioplankton Population with Reduced Genomes.PMC9426536JCYJ201805081618118994053257 & 31328094177612914163917AoE/M-403/16Cheung LSLee SYFeng XChu XCrowe SAWang XLuo HAng PfalseCoastal Transient Niches Shape the Microdiversity Pattern of a Bacterioplankton Population with Reduced Genomes.Globally dominant marine bacterioplankton lineages are often limited in metabolic versatility, owing to their extensive genome reductions, and thus cannot take advantage of transient nutrient patches. It is therefore perplexing how the nutrient-poor bulk seawater sustains the pelagic streamlined lineages, each containing numerous populations. Here, we sequenced the genomes of 33 isolates of the recently discovered CHUG lineage (~2.6 Mbp), which have some of the smallest genomes in the globally abundant Roseobacter group (commonly over 4 Mbp). These genome-reduced bacteria were isolated from a transient habitat: seawater surrounding the brown alga, Sargassum hemiphyllum. Population genomic analyses showed that: (i) these isolates, despite sharing identical 16S rRNA genes, were differentiate2022-01-01T00:00:00Z2022 Aug2026-06-13T06:03:54.597Z2025-02-19T03:28:47.014ZS-EPMC94265363588088310.1128/mbio.00571-22