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

• Published in: Aquatic Microbial Ecology
• Main Authors: Kaartokallio, H., Søgaard, D.H., Norman, L., Rysgaard, S., Tison, Jean-Louis, Delille, Bruno, Thomas, D.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Inter-Research 2013
• Subjects: Physical; chemical; mathematical & earth Sciences; Earth sciences & physical geography; Physique; chimie; mathématiques & sciences de la terre; Sciences de la terre & géographie physique; Greenland; Sea ice; Subarctic
• Online Access: https://orbi.uliege.be/handle/2268/164911; https://orbi.uliege.be/bitstream/2268/164911/1/Kaartokallio%20et%20al%202013.pdf; https://doi.org/10.3354/ame01667

peer reviewed 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. Leucine incorporation was saturated at micro molar concentrations, as known from freshwater and marine biofilm systems. Leu:TdR ratios were high (up to >300) in lowermost ice layers and when they are compared to published respiration measurements these results suggest non-specific leucine 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 leucine 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.