Assessment of Hydrocarbon Degradation Potential in Microbial Communities in Arctic Sea Ice.

The anthropogenic release of oil hydrocarbons into the cold marine environment is an increasing concern due to the elevated usage of sea routes and the exploration of new oil drilling sites in Arctic areas. The aim of this study was to evaluate prokaryotic community structures and the genetic potential of hydrocarbon degradation in the metagenomes of seawater, sea ice, and crude oil encapsulating the sea ice of the Norwegian fjord, Ofotfjorden. Although the results indicated substantial differences between the structure of prokaryotic communities in seawater and sea ice, the crude oil encapsulating sea ice (SIO) showed increased abundances of many genera-containing hydrocarbon-degrading organisms, including Bermanella, Colwellia, and Glaciecola. Although the metagenome of seawater was rich in a variety of hydrocarbon degradation-related functional genes (HDGs) associated with the metabolism of n-alkanes, and mono- and polyaromatic hydrocarbons, most of the normalized gene counts were highest in the clean sea ice metagenome, whereas in SIO, these counts were the lowest. The long-chain alkane degradation gene almA was detected from all the studied metagenomes and its counts exceeded ladA and alkB counts in both sea ice metagenomes. In addition, almA was related to the most diverse group of prokaryotic genera. Almost all 18 good- and high-quality metagenome-assembled genomes (MAGs) had diverse HDGs profiles. The MAGs recovered from the SIO metagenome belonged to the abundant taxa, such as Glaciecola, Bermanella, and Rhodobacteracea, in this environment. The genera associated with HDGs were often previously known as hydrocarbon-degrading genera. However, a substantial number of new associations, either between already known hydrocarbon-degrading genera and new HDGs or between genera not known to contain hydrocarbon degraders and multiple HDGs, were found. The superimposition of the results of comparing HDG associations with taxonomy, the HDG profiles of MAGs, and the full genomes of organisms in the KEGG database suggest that the found relationships need further investigation and verification.

Biotransformation of chemically dispersed diesel at sub-zero temperatures using artificial brines.

The biotransformation of hydrocarbon compounds in seawater at sub-zero temperature has gained research interest in recent years with the most focus placed on temperatures around 0°C. In this study, biotransformation of dispersed diesel at sub-zero temperatures (-2°C to -6°C) in artificial brines, prepared by adding Instant Ocean salt to natural seawater to increase salinity, is examined. The oil was pre-mixed with dispersant Finasol 51 to prepare the dispersed oil at 2 mg l-1. The native microorganisms in sub-arctic seawater were able to adapt to high salinity and lower temperature in the sea ice brine at tested temperatures and were capable of biotransforming hydrocarbon compounds. Complete depletion of low and middle-range molecular weight n-alkanes, 2/3 ring PAHs and their alkylated compounds was observed after 123 days at -2°C. The depletion extents of hydrocarbon compounds were reduced at -6°C in comparison with -2°C, especially for PAHs and alkylated hydrocarbons. This study suggests that: there is a potential for biodegradation of dispersed oil in sea ice brine at temperatures between -2°C and -6°C. However, for oil with high pour point, the biodegradation process will be more affected by low temperature. Therefore, to predict the fate of dispersed oil at low temperature, the biodegradation rate should be established for each individual oil type and at a specific temperature.