Eeva Eronen-Rasimus

Isolation and characterization of phage-host systems from the Baltic Sea ice.

In search for sea ice bacteria and their phages from the Baltic Sea ice, two ice samples were collected from land-fast ice in a south-west Finland coastal site in February and March 2011. Bacteria were isolated from the melted sea ice samples and phages were screened from the same samples for 43 purified isolates. Plaque-producing phages were found for 15 bacterial isolates at 3xa0°C. Ten phage isolates were successfully plaque purified and eight of them were chosen for particle purification to analyze their morphology and structural proteins. Phage 1/32 infecting an isolate affiliated to phylum Bacteroidetes (Flavobacterium sp.) is a siphovirus and six phages infecting isolates affiliated to γ-Proteobacteria (Shewanella sp.) hosts were myoviruses. Cross titrations between the hosts showed that all studied phages are host specific. Phage solutions, host growth and phage infection were tested in different temperatures revealing phage temperature tolerance up to 45xa0°C, whereas phage infection was in most of the cases retarded above 15xa0°C. This study is the first to report isolation and cultivation of ice bacteria and cold-active phages from the Baltic Sea ice.

Bacterial community dynamics and activity in relation to dissolved organic matter availability during sea-ice formation in a mesocosm experiment.

The structure of sea‐ice bacterial communities is frequently different from that in seawater. Bacterial entrainment in sea ice has been studied with traditional microbiological, bacterial abundance, and bacterial production methods. However, the dynamics of the changes in bacterial communities during the transition from open water to frozen sea ice is largely unknown. Given previous evidence that the nutritional status of the parent water may affect bacterial communities during ice formation, bacterial succession was studied in under ice water and sea ice in two series of mesocosms: the first containing seawater from the North Sea and the second containing seawater enriched with algal‐derived dissolved organic matter (DOM). The composition and dynamics of bacterial communities were investigated with terminal restriction fragment length polymorphism (T‐RFLP), and cloning alongside bacterial production (thymidine and leucine uptake) and abundance measurements (measured by flow cytometry). Enriched and active sea‐ice bacterial communities developed in ice formed in both unenriched and DOM‐enriched seawater (0–6 days). γ‐Proteobacteria dominated in the DOM‐enriched samples, indicative of their capability for opportunistic growth in sea ice. The bacterial communities in the unenriched waters and ice consisted of the classes Flavobacteria, α‐ and γ‐Proteobacteria, which are frequently found in natural sea ice in polar regions. Furthermore, the results indicate that seawater bacterial communities are able to adapt rapidly to sudden environmental changes when facing considerable physicochemical stress such as the changes in temperature, salinity, nutrient status, and organic matter supply during ice formation.

Discovery of bacterial polyhydroxyalkanoate synthase (PhaC)-encoding genes from seasonal Baltic Sea ice and cold estuarine waters.

AbstractnPolyhydroxyalkanoates (PHAs) are macromolecules produced by bacteria as means for storing carbon and energy in intracellular granules. PHAs have physical properties similar to those of plastics and have become of interest to industry as materials for environmentally friendly bioplastic production. There is an ongoing search for new PHA-producing bacterial strains and PHA-synthesizing enzymes tolerating extreme conditions to find ways of producing PHAs at cold temperatures and high solute concentrations. Moreover, the study of PHA producers in the sea-ice biome can aid in understanding the microbial ecology of carbon cycling in ice-associated ecosystems. In this study, PHA producers and PHA synthase genes were examined under the extreme environmental conditions of sea ice and cold seawater to find evidence of PHA production in an environment requiring adaptation to high salinity and cold temperatures. Sea ice and cold estuarine water samples were collected from the northern Baltic Sea and evidence of PHA production was gathered, using microscopy with Nile Blue A staining of PHA-granules and PCR assays detecting PHA-synthesis genes. The PHA granules and PHA synthases were found at all sampling locations, in both sea ice and water, and throughout the sampling period spanning over 10xa0years. Our study shows, for the first time, that PHA synthesis occurs in Baltic Sea cold-adapted bacteria in their natural environment, which makes the Baltic Sea and its cold environments an interesting choice in the quest for PHA-synthesizing bacteria and synthesis genes.

Ice formation and growth shape bacterial community structure in Baltic Sea drift ice

Drift ice, open water and under-ice water bacterial communities covering several developmental stages from open water to thick ice were studied in the northern Baltic Sea. The bacterial communities were assessed with 16S rRNA gene terminal-restriction fragment length polymorphism and cloning, together with bacterial abundance and production measurements. In the early stages, open water and pancake ice were dominated by Alphaproteobacteria and Actinobacteria, which are common bacterial groups in Baltic Sea wintertime surface waters. The pancake ice bacterial communities were similar to the open-water communities, suggesting that the parent water determines the sea-ice bacterial community in the early stages of sea-ice formation. In consolidated young and thick ice, the bacterial communities were significantly different from water bacterial communities as well as from each other, indicating community development in Baltic Sea drift ice along with ice-type changes. The thick ice was dominated by typical sea-ice genera from classes Flavobacteria and Gammaproteobacteria, similar to those in polar sea-ice bacterial communities. Since the thick ice bacterial community was remarkably different from that of the parent seawater, results indicate that thick ice bacterial communities were recruited from the rarer members of the seawater bacterial community.

An active bacterial community linked to high chl-a concentrations in Antarctic winter-pack ice and evidence for the development of an anaerobic sea-ice bacterial community

Antarctic sea-ice bacterial community composition and dynamics in various developmental stages were investigated during the austral winter in 2013. Thick snow cover likely insulated the ice, leading to high (<4u2009μgu2009l–1) chlorophyll-a (chl-a) concentrations and consequent bacterial production. Typical sea-ice bacterial genera, for example, Octadecabacter, Polaribacter and Glaciecola, often abundant in spring and summer during the sea-ice algal bloom, predominated in the communities. The variability in bacterial community composition in the different ice types was mainly explained by the chl-a concentrations, suggesting that as in spring and summer sea ice, the sea-ice bacteria and algae may also be coupled during the Antarctic winter. Coupling between the bacterial community and sea-ice algae was further supported by significant correlations between bacterial abundance and production with chl-a. In addition, sulphate-reducing bacteria (for example, Desulforhopalus) together with odour of H2S were observed in thick, apparently anoxic ice, suggesting that the development of the anaerobic bacterial community may occur in sea ice under suitable conditions. In all, the results show that bacterial community in Antarctic sea ice can stay active throughout the winter period and thus possible future warming of sea ice and consequent increase in bacterial production may lead to changes in bacteria-mediated processes in the Antarctic sea-ice zone.

Life associated with Baltic Sea ice

1. n nThe formation of sea ice impacts directly on the physical dynamics of water masses (e.g. wind stress at the sea surface) and air-sea exchange processes (e.g. vertical heat fluxes). n n n n n2. n nThe annual cycle of formation, consolidation and melting of sea ice has a major influence on the ecology of both the benthic and pelagic components of the Baltic Sea ecosystem. n n n n n3. n nThere is considerable inter-annual variation in the extent of sea ice in the Baltic Sea and thus in the size of the habitat for sympagic (ice-associated) microbial and metazoan communities as well as for larger organisms living on the ice, notably the ringed seal. n n n n n4. n nThere is a pronounced gradient in ice characteristics, from more saline ice in the south of the Baltic Sea to freshwater ice in the north. The former is more porous and supports more ice-associated biology than the latter. n n n n n5. n nThe Baltic sympagic communities consist mainly of prokaryotic and eukaryotic microbes (bacteria, diatoms, dinoflagellates, flagellates), ciliates and rotifers. These communities are recruited from the plankton when the ice forms, followed by an ice-adapted successional pattern with an expansion of substrate-bound pennate diatoms, which does not occur in the seawater beneath the ice. n n n n n6. n nThe sea-ice food webs inside the ice are truncated compared to the open-water food webs because organisms larger than the upper size limit of the brine channels are lacking in the internal sympagic communities. n n n n n7. n nGlobal climate change decreases the extension and thickness of the sea ice as well as the length of the ice season, and therefore the seasonal effects that sea ice has on the Baltic Sea winter-spring ecosystem dynamics.

Bacterial communities in Arctic first-year drift ice during the winter/spring transition.

Horizontal and vertical variability of first-year drift-ice bacterial communities was investigated along a North-South transect in the Fram Strait during the winter/spring transition. Two different developmental stages were captured along the transect based on the prevailing environmental conditions and the differences in bacterial community composition. The differences in the bacterial communities were likely driven by the changes in sea-ice algal biomass (2.6-5.6 fold differences in chl-a concentrations). Copiotrophic genera common in late spring/summer sea ice, such as Polaribacter, Octadecabacter and Glaciecola, dominated the bacterial communities, supporting the conclusion that the increase in the sea-ice algal biomass was possibly reflected in the sea-ice bacterial communities. Of the dominating bacterial genera, Polaribacter seemed to benefit the most from the increase in algal biomass, since they covered approximately 39% of the total community at the southernmost stations with higher (>6 μg l(-1) ) chl-a concentrations and only 9% at the northernmost station with lower chl-a concentrations (<6 μg l(-1) ). The sea-ice bacterial communities also varied between the ice horizons at all three stations and thus we recommend that for future studies multiple ice horizons be sampled to cover the variability in sea-ice bacterial communities in spring.

Autochthonous Dissolved Organic Matter Drives Bacterial Community Composition during a Bloom of Filamentous Cyanobacteria

The dynamics of dissolved organic matter (DOM) and the succession of bacterial community composition (BCC) were investigated during bloom of filamentous cyanobacteria in a mesocosm experiment conducted in the western Gulf of Finland, the Baltic Sea. The effects of labile dissolved organic carbon (glucose), inorganic nutrients (N and P) and large zooplankton (> 100 µm) on the DOM pool, bacterial production and the composition of bacterial communities were analysed over a period of ten days. In addition, the bioavailability of dissolved organic carbon (DOC) and its turnover by heterotrophic bacteria (biomass and respiration) were investigated in three one-week bacterial bioassays. Heterotrophic bacteria rapidly utilised about 25-55 % of the DOC released from the plankton community, thus assuming it to be highly labile DOC. More than half of the accumulating net DOC pool was degraded over seven days, thus assuming it to be labile. In average, labile autochthonous DOC was degraded with bacterial growth efficiency of 25%. A distinct succession of bacterial communities accompanied the supply of autochthonous DOM, with the most prominent responses occurring in a few single phylotypes of the Delta- and Gammaproteobacterial classes. About 40% of the variation in the relative shares of dominant bacterial classes could be explained by changes in the functional groups of autotrophs. Inorganic nutrient treatment proved beneficial to Deltaproteobacteria and increased bacterial production over that of other mesocosms.

The first known virus isolates from Antarctic sea ice have complex infection patterns

Abstract Viruses are recognized as important actors in ocean ecology and biogeochemical cycles, but many details are not yet understood. We participated in a winter expedition to the Weddell Sea, Antarctica, to isolate viruses and to measure virus‐like particle abundance (flow cytometry) in sea ice. We isolated 59 bacterial strains and the first four Antarctic sea‐ice viruses known (PANV1, PANV2, OANV1 and OANV2), which grow in bacterial hosts belonging to the typical sea‐ice genera Paraglaciecola and Octadecabacter. The viruses were specific for bacteria at the strain level, although OANV1 was able to infect strains from two different classes. Both PANV1 and PANV2 infected 11/15 isolated Paraglaciecola strains that had almost identical 16S rRNA gene sequences, but the plating efficiencies differed among the strains, whereas OANV1 infected 3/7 Octadecabacter and 1/15 Paraglaciecola strains and OANV2 1/7 Octadecabacter strains. All the phages were cold‐active and able to infect their original host at 0°C and 4°C, but not at higher temperatures. The results showed that virus‐host interactions can be very complex and that the viral community can also be dynamic in the winter‐sea ice. Figure. No Caption available.