Sub-Arctic bacterioplankton in-situ response to crude oil and identification of the oil-degrading community by DNA-SIP and cultivation

Microbes play a central role in the degradation of chemical pollutants in the oceans, yet most studies investigating this are conducted in a laboratory setting which does not accurately portray and account for the prevailing physical and geochemical conditions in the deep sea. The Faroe-Shetland Channel (FSC) is a deep water, sub-Arctic region to the north of Scotland with >40-yr history of oil exploration and production. Here, we investigate the bacterioplankton community response to crude oil by enclosing water samples from ~500m depth in dialysis bags and incubating them in-situ to account for the role of environmental conditions. Using barcoded-amplicon 16S rRNA sequencing, the community strongly and rapidly responded to the oil within 4 days, particularly dominated by members of the genera Pseudoalteromonas, Alcanivorax, Mesonia, Alteromonas, and to a lesser extent Sulfitobacter, Vibrio and Thalassospira. Intriguingly, typical psychrophilic oil-degraders like Colwellia and Oleispira were not enriched, possibly due to being outcompeted by better adapted, more 'aggressive' hydrocarbon-degraders at this water depth. Using cultivation-based methods coupled with DNA-based stable isotope probing (DNA-SIP), we identified a diversity of oil-degraders, some of which (i.e. Mesonia, Spongiispira, Stutzerimonas, Vreelandella, Sulfitobacter, Paraglaciecola) had not hitherto been found in sequencing surveys or confirmed as oil-degraders in the FSC. Collectively, we show for the first time the presence of a diverse hydrocarbon-degrading community in the FSC that 'stands at the ready' to consume oil that may become entrained within the the subsurface at depth in the event of a spill in this region.