Hydrocarbon-degrading microbial populations in permanently cold deep-sea sediments in the NW Atlantic

Permanently cold deep-sea sediments (2500–3500 m water depth) with and without indications of thermogenic hydrocarbon seepage were exposed to naphtha to examine the presence and potential of cold-adapted aerobic hydrocarbon-degrading microbial populations. Monitoring these microcosms for volatile hydrocarbons by GC–MS revealed sediments without in situ hydrocarbons responded more rapidly to naphtha amendment than hydrocarbon seep sediments overall, but seep sediments removed aromatic hydrocarbons benzene, toluene, ethylbenzene and xylene (BTEX) more readily. Naphtha-driven aerobic respiration was more evident in surface sediment (0–20 cmbsf) than deeper anoxic layers (>130 cmbsf) that responded less rapidly. In all cases, enrichment of Gammaproteobacteria included lineages of Oleispira, Pseudomonas, and Alteromonas known to be associated with marine oil spills. On the other hand, taxa known to be prevalent in situ and diagnostic for thermogenic hydrocarbon seepage in deep sea sediment, did not respond to naphtha amendment. This suggests a limited role for these prevalent seep-associated populations in the context of aerobic hydrocarbon biodegradation.