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

Angela Peeb,Hiie Nõlvak,Marika Truu,Nga Phuong Dang,Jaak Truu,Chris Petrich

doi:10.3390/microorganisms10020328

Abstract

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.

Highlights

Oceans cover over 70% of the Earth’s surface and the extremely variable conditions in these ecosystems are challenging for microorganisms, such as bacteria or archaea, to adapt to [1]
The metagenomic analysis of this study revealed notable differences in terms of the structure of prokaryotic communities and hydrocarbon degradation potential between the Arctic seawater and sea ice, whereas the encapsulated oil led to considerable shifts in microbial community structure and hydrocarbon degradation potential in sea ice
Pelagibacter has been shown to occur at the end of the oil biodegradation period in Arctic seawater and is related to the microbial community’s return to baseline conditions preceding contamination [62]; the results of this study suggest that the organisms from this genus might directly contribute to hydrocarbon degradation in Arctic seawater and sea ice

Summary

Introduction

Oceans cover over 70% of the Earth’s surface and the extremely variable conditions in these ecosystems are challenging for microorganisms, such as bacteria or archaea, to adapt to [1]. In the Arctic marine environment, the risk of oil spills is increasing due to climate change that enables the prolonged and more frequent usage of Arctic sea routes [5,6]. Oil spill cleanups in Arctic regions present a challenge due to poorly accessible locations and extreme weather, both of which can complicate or totally impede the usage of traditional oil spill cleanup methods such as booms, skimmers, and pumping systems [9,10]

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Discussion

Conclusion