AME 71:57-73 (2013)  -  DOI:

Short-term variability in bacterial abundance, cell properties, and incorporation of leucine and thymidine in subarctic sea ice

H. Kaartokallio1,*, D. H. Søgaard2,3, L. Norman4, S. Rysgaard2,5,6, J.-L. Tison7, B. Delille8, D. N. Thomas1,4,5

1Marine Research Center, Finnish Environment Institute, Erik Palmenin aukio 1 00560, Helsinki, Finland
2Greenland Climate Research Centre, c/o Greenland Institute of Natural Resources, Kivioq 2, Nuuk 3900, Greenland
3University of Southern Denmark, Campusvej 55, 5230 Odense M, Denmark
4School of Ocean Sciences, Bangor University, Menai Bridge, Anglesey LL59 5AB, UK
5Arctic Research Centre, Aarhus University, C.F. Møllers Allé 8, Bldg. 1110, 8000 Aarhus C, Denmark
6Centre for Earth Observation Science, 535 Wallace Building, University of Manitoba, Winnipeg R3T 2N2, Canada
7Glaciology Unit, Department of Earth and Environmental Science, Université Libre de Bruxelles, ULB CP 160/03 50 Avenue F. D. Roosevelt, 1050 Bruxelles, Belgium
8Unité d’Océanographie Chimique, MARE, Université de Liège, Allé du 6 Août, 17–4000 Liège, Belgium

ABSTRACT: Sea ice is a biome of immense size and provides a range of habitats for diverse microbial communities, many of which are adapted to living at low temperatures and high salinities in brines. We measured simultaneous incorporation of thymidine (TdR) and leucine (Leu), bacterial cell abundance and cell population properties (by flow cytometry) in subarctic sea ice in SW Greenland. Short-term temporal variability was moderate, and steep environmental gradients, typical for sea ice, were the main drivers of the variability in bacterial cell properties and activity. Low nucleic acid (LNA) bacteria, previously linked to oligotrophic ecotypes in marine habitats, were more abundant in the upper ice layers, whereas high nucleic acid (HNA) bacteria dominated in lower ice, where organic carbon was in high concentrations. Leu incorporation was saturated at micromolar concentrations, as known from freshwater and marine biofilm systems. Leu:TdR ratios were high (up to >300) in lowermost ice layers, and when compared to published respiration measurements, these results suggest non-specific Leu incorporation. There was evidence of polyhydroxyalkanoate (PHA)-containing bacteria in the sea ice, shown by brightly fluorescing intracellular inclusions after Nile Blue A staining. High Leu saturating concentrations coupled with the occurrence of PHA-producing organisms further highlight the similarity of sea ice internal habitats to biofilm-like systems rather than to open-water systems.

KEY WORDS: Sea ice · Bacteria · Temporal variability · Leucine · Thymidine · Flow cytometry · Polyhydroxyalkanoates

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Cite this article as: Kaartokallio H, Søgaard DH, Norman L, Rysgaard S, Tison JL, Delille B, Thomas DN (2013) Short-term variability in bacterial abundance, cell properties, and incorporation of leucine and thymidine in subarctic sea ice. Aquat Microb Ecol 71:57-73.

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