ORIGINAL ARTICLE Responses of Microbial Communities in Arctic Sea Ice After Contamination by Crude Petroleum Oil Odd Gunnar Brakstad & Ingunn Nonstad & Liv-Guri Faksness & Per Johan Brandvik Received: 16 February 2007 / Accepted: 30 June 2007 / Published online: 6 September 2007 # Springer Science + Business Media, LLC 2007 Abstract Microbial communities associated with Arctic fjord ice polluted with petroleum oils were investigated in this study. A winter field experiment was conducted in the Van Mijen Fjord (Svalbard) from February to June 2004, in which the ice was contaminated with a North Sea paraffinic oil. Holes were drilled in the ice and oil samples frozen into the ice at the start of the experiment. Samples, including cores of both oil-contaminated and clean ice, were collected from the field site 33, 74, and 112 days after oil application. The sampled cores were separated into three sections and processed for microbiological and chemical analyses. In the oil-contaminated cores, enumerations of total prokaryotic cells by fluorescence microscopy and colony-forming units (CFU) counts of heterotrophic prokaryotes both showed stimulation of microbial growth, while concentrations of oil-degrading prokaryotes remained at similar levels in contaminated and clean ice. Analysis of polymerase chain reaction (PCR)-amplified bacterial 16S rRNA gene frag- ments by denaturing gradient gel electrophoresis (DGGE) revealed that bacterial communities in oil-contaminated ice generated fewer bands than communities in clean ice, although banding patterns changed both in contaminated and clean ice during the experimental period. Microbial communities in unpolluted ice and in cores contaminated with the paraffinic oil were examined by cloning and sequence analysis. In the contaminated cores, the commu- nities became predominated by Gammaproteobacteria related to the genera Colwellia, Marinomonas, and Glacie- cola, while clean ice included more heterogeneous pop- ulations. Chemical analysis of the oil-contaminated ice cores with determinations of n-C17/Pristane and naphtha- lene/phenanthrene ratios indicated slow oil biodegradation in the ice, primarily in the deeper parts of the ice with low hydrocarbon concentrations. Introduction Oil exploration and production are increasing in Arctic regions. Although environmental and safety issues are highly emphasized in these areas, the risks of accidental discharges are relevant, both from the increasing oil exploration, production, and transport activities. Oil pollu- tions may be transported to the ice margins of the Arctic oceans by prevailing seawater currents, where the oil becomes infested in the ice. Drifting ice may further transport pollutions and release them during melting far from the source areas [46]. Investigations of the fate of ice- infested oils are therefore important, as part of the risk assessment related to petroleum activities in the Arctic, including the possible stimulation of indigenous hydro- carbonoclastic microbes in the Arctic sea ice. In cold climates, psychrophilic and psychrotolerant microorganisms are important for degradation of organic pollutants. Polar sea ice includes typical psychrophilic bacteria belonging to the phyla Proteobacteria and Bacteroidetes [4, 9, 10, 35], and microbial concentrations >10 6 cells/ml have been measured in the ice [30]. Microb Ecol (2008) 55:540–552 DOI 10.1007/s00248-007-9299-x O. G. Brakstad (*) : P. J. Brandvik SINTEF Materials and Chemistry, Division of Marine Environmental Technology, Brattørkaia 17B, N-7465, Trondheim, Norway e-mail: odd.g.brakstad@sintef.no I. Nonstad Department of Biotechnology, Norwegian University of Science and Technology, Trondheim, Norway L.-G. Faksness Department of Arctic Technology, University Centre in Svalbard, Longyearbyen, Norway