Microbial communities related to biodegradation of dispersed <scp>M</scp>acondo oil at low seawater temperature with Norwegian coastal seawater

<jats:title>Summary</jats:title><jats:p>The <jats:styled-content style="fixed-case">D</jats:styled-content>eepwater <jats:styled-content style="fixed-case">H</jats:styled-content>orizon (<jats:styled-content style="fixed-case">DWH</jats:styled-content>) accident in 2010 created a deepwater plume of small oil droplets from a deepwater well in the <jats:styled-content style="fixed-case">M</jats:styled-content>ississippi <jats:styled-content style="fixed-case">C</jats:styled-content>anyon lease block 252 (‘<jats:styled-content style="fixed-case">M</jats:styled-content>acondo oil’). A novel laboratory system was used in the current study to investigate biodegradation of <jats:styled-content style="fixed-case">M</jats:styled-content>acondo oil dispersions (10 μm or 30 μm median droplet sizes) at low oil concentrations (2 mg l<jats:sup>−1</jats:sup>) in coastal <jats:styled-content style="fixed-case">N</jats:styled-content>orwegian seawater at a temperature of 4–5°C. Whole metagenome analyses showed that oil biodegradation was associated with the successive increased abundances of Gammaproteobacteria, while <jats:styled-content style="fixed-case">A</jats:styled-content>lphaproteobacteria (<jats:styled-content style="fixed-case"><jats:italic>P</jats:italic></jats:styled-content><jats:italic>elagibacter</jats:italic>) became dominant at the end of the experiment. <jats:italic>Colwellia</jats:italic> and <jats:styled-content style="fixed-case">O</jats:styled-content>ceanospirillales were related to n‐alkane biodegradation, while particularly <jats:styled-content style="fixed-case"><jats:italic>C</jats:italic></jats:styled-content><jats:italic>ycloclasticus</jats:italic> and <jats:styled-content style="fixed-case"><jats:italic>M</jats:italic></jats:styled-content><jats:italic>arinobacter</jats:italic> were associated with degradation of aromatic hydrocarbons (<jats:styled-content style="fixed-case">HC</jats:styled-content>s). The larger oil droplet dispersions resulted in delayed sequential changes of <jats:styled-content style="fixed-case">O</jats:styled-content>ceanospirillales and <jats:styled-content style="fixed-case"><jats:italic>C</jats:italic></jats:styled-content><jats:italic>ycloclasticus</jats:italic>, related with slower degradation of alkanes and aromatic HCs. The bacterial successions associated with oil biodegradation showed both similarities and differences when compared with the results from <jats:styled-content style="fixed-case">DWH</jats:styled-content> field samples and laboratory studies performed with deepwater from the <jats:styled-content style="fixed-case">G</jats:styled-content>ulf of <jats:styled-content style="fixed-case">M</jats:styled-content>exico.</jats:p>