AbstractsBiology & Animal Science

Ice formation, growth and associated substrate supply determine sea-ice bacterial community dynamics

by Eeva Eronen-Rasimus

Institution: University of Helsinki
Department: Department of Food and Environmental Sciences, Mikrobiologian ja biotekniikan osasto; Finnish Environment Institute, Marine Centre;Tvärminne Zoological Station, University of Helsinki
Year: 2015
Keywords: mikrobiologia
Record ID: 1146029
Full text PDF: http://hdl.handle.net/10138/154541


Sea ice, at its maximum extent, is one of the largest biomes on Earth. In addition to the polar oceans, it covers extensive sea areas at lower latitudes such as the Baltic Sea and the Sea of Okhotsk. During ice formation, organic and inorganic components in the parent seawater are concentrated into saline brines within the ice, which serve as a habitat for diverse auto- and heterotrophic organisms, including bacteria. Sea-ice bacteria are responsible for many biogeochemical processes, such as decomposition of particulate organic matter, recycling of dissolved organic matter and remineralization of nutrients, analogously to bacterially driven biogeochemical processes in the water column. Since bacterial groups vary by their metabolic traits and participation in biogeochemical processes, knowledge of the bacterial community structure and its seasonal variation is essential for an understanding of ice biogeochemistry. This thesis characterises sea-ice bacterial communities during ice formation and during the winter/spring transition phase when the community composition is poorly known. Bacterial communities in Arctic and Baltic sea ice during the winter/spring transition were studied and compared. In addition, the effect of the dissolved organic matter regime on bacterial community formation was investigated in an experimental sea-ice system with North Sea water. The main methods applied were terminal-restriction fragment length polymorphism and/or Illumina Miseq sequencing together with bacterial production and abundance measurements. During the early stages of sea-ice formation, the bacterial communities were similar to the parent water communities, suggesting that the parent water determines the initial sea-ice bacterial community composition. After congealment of the sea ice, the bacterial communities changed towards communities typical of sea ice in spring. During the winter/spring transition, members of the classes Flavobacteriia (formerly Flavobacteria), Gammaproteobacteria and Alphaproteobacteria were predominant both in Baltic and Arctic sea ice. The Baltic and Arctic sea-ice bacterial communities were significantly different; however, a few members of common sea-ice bacterial genera, such as Polaribacter and Shewanella, were closely related, pointing to similar selection in ice, regardless of differences in the prevailing environmental conditions. In the experimental system, the bacterial communities were able to respond to altered substrate availability immediately after ice formation. This indicates successful adaptation of sea-ice bacteria to major shifts in temperature and salinity during ice formation. The results of this thesis suggest that sea-ice bacterial community formation and dynamics is defined by a combination of changes in environmental conditions during sea-ice maturation and its associated substrate availability, as well as resource competition. The sea-ice habitat provides an example of the enormous capacity of bacteria to adapt to changing environments and how minor members of the…