LAUSR

Oil spills in the subarctic marine environment off the coast of Labrador, Canada, are increasingly likely due to potential oil production and increases in ship traffic in the region. To understand the microbiome response and how nutrient biostimulation promotes biodegradation of oil spills in this cold marine setting, marine sediment microcosms amended with diesel or crude oil were incubated at in situ temperature (4°C) for several weeks. Sequencing of 16S rRNA genes following these spill simulations revealed decreased microbial diversity and enrichment of putative hydrocarbonoclastic bacteria that differed by petroleum product. Metagenomic sequencing revealed Paraperlucidibaca and Cycloclasticus harbour previously unrecognized capabilities for alkane biodegradation. Genomic and amplicon sequencing together suggest that Oleispira and Thalassolituus degraded alkanes from diesel, while Zhongshania and the novel PGZG01 lineage contributed to crude oil alkane biodegradation. Greater losses in PAHs from crude oil than from diesel were consistent with Marinobacter, Pseudomonas_D and Amphritea genomes exhibiting aromatic hydrocarbon biodegradation potential. Biostimulation with nitrogen and phosphorus (4.67 mM NH4Cl; 1.47 mM KH2PO4) was effective at enhancing n-alkane and PAH degradation following low concentration (0.1% v/v) diesel and crude oil amendments, while at higher concentrations (1% v/v) only n-alkanes in diesel were consumed, suggesting toxicity induced by compounds in unrefined crude oil. Biostimulation allowed for a more rapid turnover in the microbial community in response to petroleum amendments, more than doubling the rates of CO2 increase during the first few weeks of incubation. Importance Increases in transportation of diesel and crude oil in the Labrador Sea will pose a significant threat to remote benthic and shoreline environments, where coastal communities and wildlife are particularly vulnerable to oil spill contaminants. Whereas marine microbiology has not been incorporated into environmental assessments in the Labrador Sea, there is a growing demand for microbial biodiversity evaluations given the pronounced impact of climate change in this region. Benthic microbial communities are important to consider given that a fraction of spilled oil typically sinks such that its biodegradation occurs at the seafloor, where novel taxa with previously unrecognized potential to degrade hydrocarbons were discovered in this work. Understanding how cold-adapted microbiomes catalyze hydrocarbon degradation at low in situ temperature is crucial in the Labrador Sea, which remains relatively cold throughout the year.