Characterization of the first cultivated strain of the SAR86 clade, isolated from the tropical Pacific Ocean

While cultivation-independent approaches to microbial ecology and evolution have brought on an unprecedented era of data volume and accessibility, the need for isolated strains that represent naturally abundant microorganisms continues to hinder the interpretation of this resource and thus our understanding of Earth’s natural systems. Despite steady progress and notable success stories, many abundant marine bacteria and archaea identified through metagenomic sequencing approaches remain uncultured. Among them is the globally distributed gammaproteobacterial clade known as SAR86. Members of this lineage were first reported in 1991 from a ribosomal RNA gene clone library constructed from surface seawater of the Sargasso Sea, and have since been found to be a ubiquitous member of the global surface ocean. Here we report the isolation of the first SAR86 cultivar, strain HIMB1674, originating from surface seawater of Kāne’ohe Bay, Hawai’i, in the coastal tropical Pacific Ocean, via a high throughput dilution culture approach. Phylogenomic and rRNA gene-based analyses place HIMB1674 within a deeply branching subclade of SAR86 known as SAR156, where it is closely related to single cell genomes recovered previously from multiple locations in the Atlantic Ocean. Interpretation of the 1639 genes annotated within the 1.62 Mbp, 36.3% GC content closed genome of HIMB1674 has revealed potential features which allow SAR86 to successfully compete for resources in the global ocean, as well as features that distinguish major subclades of SAR86 marine bacteria.