Ecotype diversification of an abundant Roseobacter lineage

Summary The Roseobacter DC5‐80‐3 cluster (also known as the RCA clade) is among the most abundant bacterial lineages in temperate and polar oceans. Previous studies revealed two phylotypes within this cluster that are distinctly distributed in the Antarctic and other ocean provinces. Here, we report a nearly complete genome co‐assembly of three closely related single cells co‐occurring in the Antarctic, and compare it to the available genomes of the other phylotype from ocean regions where iron is more accessible but phosphorus and nitrogen are less. The Antarctic phylotype exclusively contains an operon structure consisting of a dicitrate transporter fecBCDE and an upstream regulator likely for iron uptake, whereas the other phylotype consistently carry a high‐affinity phosphate pst transporter and the phoB ‐ phoR regulatory system, a high‐affinity ammonium amtB transporter, urea and taurine utilization systems. Moreover, the Antarctic phylotype