Generalist hydrocarbon‐degrading bacterial communities in the oil‐polluted water column of the <scp>N</scp>orth <scp>S</scp>ea

<jats:title>Summary</jats:title><jats:p>The aim of this work was to determine the effect of light crude oil on bacterial communities during an experimental oil spill in the <jats:styled-content style="fixed-case">N</jats:styled-content>orth <jats:styled-content style="fixed-case">S</jats:styled-content>ea and in mesocosms (simulating a heavy, enclosed oil spill), and to isolate and characterize hydrocarbon‐degrading bacteria from the water column. No oil‐induced changes in bacterial community (3 m below the sea surface) were observed 32 h after the experimental spill at sea. In contrast, there was a decrease in the dominant <jats:styled-content style="fixed-case">SAR</jats:styled-content>11 phylotype and an increase in <jats:styled-content style="fixed-case"><jats:italic>P</jats:italic></jats:styled-content><jats:italic>seudoalteromonas</jats:italic> spp. in the oiled mesocosms (investigated by 16<jats:styled-content style="fixed-case">S rRNA</jats:styled-content> gene analysis using denaturing gradient gel electrophoresis), as a consequence of the longer incubation, closer proximity of the samples to oil, and the lack of replenishment with seawater. A total of 216 strains were isolated from hydrocarbon enrichment cultures, predominantly belonging to the genus <jats:styled-content style="fixed-case"><jats:italic>P</jats:italic></jats:styled-content><jats:italic>seudoaltero monas</jats:italic>; most strains grew on <jats:styled-content style="fixed-case">PAHs</jats:styled-content>, branched and straight‐chain alkanes, as well as many other carbon sources. No obligate hydrocarbonoclastic bacteria were isolated or detected, highlighting the potential importance of cosmopolitan marine generalists like <jats:styled-content style="fixed-case"><jats:italic>P</jats:italic></jats:styled-content><jats:italic>seudoalteromonas</jats:italic> spp. in degrading hydrocarbons in the water column beneath an oil slick, and revealing the susceptibility to oil pollution of <jats:styled-content style="fixed-case">SAR</jats:styled-content>11, the most abundant bacterial clade in the surface ocean.</jats:p>