Diversity and function of microbial communities in the Arctic Ocean

The Arctic Ocean ecosystem is rapidly changing in response to climate warming. The ongoing decline of its sea-ice cover has raised many questions as to the ecological consequences on biodiversity, primary productivity, and the biological carbon pump. The diversity and function of bacterial communities in the Arctic Ocean has been little explored, despite their often important role in biogeochemical cycling. One objective of this thesis was therefore to improve the current knowledge of microbial community diversity in the most understudied region of the Arctic Ocean, the deep central Eurasian basin. As sea-ice reduction is altering primary productivity and biological transport processes from the surface ocean to the deep sea, another focus of this thesis was the identification of bacterial groups associated to freshly formed, sinking and deposited particulate organic matter. Finally, the underlying genomic features that deep-sea surface sediment bacteria use for carbon turnover were analyzed, as the degradation of organic matter by heterotrophic bacteria in deep-sea sediments regulates the efficiency of CO2 removal from the atmosphere over geological time scales

Body size of Pecten maximus (Mollusca, Bivalvia) is nega- tively correlated with frequency of escape response elicited by its predator Asterias rubens

Prey and predatior relations are complex and depend on several factors. One of theseis the size difference between predator and prey. The dependence of the frequency of the escape response to the body size difference is tested by using different sizes of the bivalve Pecten maximus and its common predator, the sea star Asterias rubens. All tests were run under laboratory conditions. The trials show, that the frequency of the escape response depends on the prey size and not on the size of the predator. With an increasing mussel size the frequency of the escape response decreases. The results are consistent with the hypothesis that smaller individuals suffer from a higher predation pressure than bigger ones and have to react in the presence of A. rubens. The hypothesis that bigger individuals only react in the presence of a big predator is rejected. Not reacting to the presence of a predator may ultimately be adventageous by saving energy. We also noted that reaction intensity is influenced by different maintenance conditions of P. maximus.Beute- und Raubtierbeziehungen sind komplex und hängen von mehreren Faktoren ab. Einer davon ist der Größenunterschied zwischen Räuber und Beute. Die Abhängigkeit der Häufigkeit der Fluchtreaktion vom Körpergrößenunterschied wird anhand unterschiedlicher Größen der Muschel Pecten maximus und ihres gemeinsamen Räubers, des Seesterns Asterias rubens, getestet. Alle Tests wurden unter Laborbedingungen durchgeführt. Die Versuche zeigen, dass die Häufigkeit der Fluchtreaktion von der Beutegröße und nicht von der Größe des Räubers abhängt. Mit zunehmender Muschelgröße nimmt die Häufigkeit der Fluchtreaktion ab. Die Ergebnisse stimmen mit der Hypothese überein, dass kleinere Individuen unter einem höheren Prädationsdruck leiden als größere und auf A. rubens reagieren müssen. Die Hypothese, dass größere Individuen nur in Gegenwart eines großen Raubtiers reagieren, wird abgelehnt. Auf die Anwesenheit eines Raubtiers nicht zu reagieren, kann letztendlich durch Energieeinsparungen vorteilhaft sein. Wir haben auch festgestellt, dass die Reaktionsintensität durch unterschiedliche Erhaltungsbedingungen von P. maximus beeinflusst wird.Peer Reviewe

Polysaccharide degradation potential of bacterial communities in Arctic deep-sea sediments (1200-5500 m water depth)

The majority of the Earth’s surface is covered by fine-grained deep-sea sediments, with bacteria dominating total benthic biomass. These benthic bacterial communities depend on organic matter input from the upper ocean, but as they comprise mostly unknown and uncultivated taxa, we have very limited knowledge of their enzymatic machinery to break down this material. Here we studied deep-sea surface sediments along a seafloor depth gradient from 1000 to 5500 m at the Arctic long-term ecological research station HAUSGARTEN. We applied Illumina 16S rRNA gene surveys based on DNA and cDNA and metagenomic sequencing to elucidate total and active bacterial community composition, and the key functional potentials. Some sequence-dominant taxa of the total community (e.g. members of the Gamma- and Deltaproteobacteria) were underrepresented in the cDNA fraction, while other groups (e.g. Flavobacteriaceae; SAR202 clade) were overrepresented in the active fraction when compared to total community reads. We used the Carbohydrate Active Enzymes database (http://www.cazy.org) to identify protein families in the generated metagenomes, which are associated with polysaccharide degradation, e.g. glycoside hydrolases. We found the same families of glycoside hydrolases in all metagenomes, but their relative contribution to glycoside hydrolase-coding genes varied according to depth. A larger number of hydrolases involved in polysaccharide degradation of algae material (e.g. for laminarin; xylan) was found at shallower depths, while those responsible for the breakdown of bacterial cell walls (e.g. for components of peptidoglycan) were more strongly represented at deep stations. Our findings indicate an adaptation of the communities to differences in organic matter quality

Journey to the deep sea: Do Arctic sea-ice bacteria hitchhike on ice-algal aggregates?

In 2012 Arctic sea ice declined to a record minimum. As a consequence of the melting, large sub-ice filaments of the diatom Melosira arctica were released and sank to the seafloor, resulting in a widespread deposition of fresh ice-algal material at 4400 m water depth. Elevated rates of oxygen consumption in sediments with algal deposits indicated remineralization by bacteria and evidenced a response of the entire ecosystem down to the deep sea to elevated carbon flux rates (Boetius et al. 2013, Science 339: 1430-1432). Bacteria play essential roles in carbon and nutrient cycling not only at the seafloor but also in the sea ice and in the water column, contributing significantly to Arctic ecosystem functioning. We sampled a wide range of Arctic environments from the surface to the deep sea, in order to compare bacterial communities from sea ice, melt ponds, surface seawater, deep-sea sediment with and without algal aggregates. Structure and composition of bacterial communities showed strong environmental specificity, with distinct differences between surface and deep-sea environments. Yet, some taxa were shared between algae aggregates from the surface and the seafloor, suggesting a transport of surface-derived bacteria to the deep ocean, as a consequence of rapid sea-ice melt

Pancreatic polypeptide inhibits somatostatin secretion

AbstractPancreatic polypeptide (PP) is a major agonist for neuropeptide Y4 receptors (NPY4R). While NPY4R has been identified in various tissues, the cells on which it is expressed and its function in those cells has not been clearly delineated. Here we report that NPY4R is present in all somatostatin-containing cells of tissues that we tested, including pancreatic islets, duodenum, hippocampus, and hypothalamus. Its agonism by PP decreases somatostatin secretion from human islets. Mouse embryonic hippocampal (mHippo E18) cells expressed NPY4Rs and their activation by PP consistently decreased somatostatin secretion. Furthermore, central injection of PP in mice induced c-Fos immunoreactivity in somatostatin-containing cells in the hippocampus compared with PBS-injected mice. In sum, our results identify PP as a pivotal modulator of somatostatin secretion

Towards an integrated microbial observatory in the Arctic Ocean

The Fram Strait separates Northeast Greenland from the Svalbard Archipelago, and is the only deep connection to the Arctic Ocean. Therefore, this strait is the only gateway for direct exchange of intermediate and deep waters between the Arctic Ocean and the North Atlantic. Two main currents influence the exchanges: i) the West Spitsbergen Current, bringing Atlantic waters northwards, and ii) the East Greenland Current, which carries cold Arctic waters and ice southwards. These two currents consist of water masses with different origin, generate distinct physical and chemical conditions between the eastern and western parts of the strait, which effects the biological characteristics in this region. Oceanographic observations in the Fram Strait have been carried out for ~15 years with microbial research in the water column focusing mainly on eukaryotes, while very little exploratory work was conducted on pelagic Bacteria and Archaea. Here we present a preliminary report of the first extensive survey across the waters of the Fram Strait focused on Bacterial and Archaeal domains, conducted as part of the Arctic long-term observatory HAUSGARTEN annual expedition in summer 2016. Besides the investigation of “who is out there”, the observations gained in this survey will be integrated with other biological and physical data of the long-term observatory framework and will provide an essential step towards the understanding of the biochemical dynamics in the Fram Strait. In addition, on a long-term plan this project will contribute to the microbial observatory work as part of the FRAM Helmholtz research infrastructure and EU AtlantOS program

Diazotroph diversity in the sea ice, melt ponds and surface waters of the Eurasian Basin of the Central Arctic Ocean

The Eurasian basin of the Central Arctic Ocean is nitrogen limited, but little is known about the presence and role of nitrogen-fixing bacteria. Recent studies have indicated the occurrence of diazotrophs in Arctic coastal waters potentially of riverine origin. Here, we investigated the presence of diazotrophs in ice and surface waters of the Central Arctic Ocean in the summer of 2012. We identified diverse communities of putative diazotrophs through targeted analysis of the nifH gene, which encodes the iron protein of the nitrogenase enzyme. We amplified 529 nifH sequences from 26 samples of Arctic melt ponds, sea ice and surface waters. These sequences resolved into 43 clusters at 92% amino acid sequence identity, most of which were non-cyanobacterial phylotypes from sea ice and water samples. One cyanobacterial phylotype related to Nodularia sp. was retrieved from sea ice, suggesting that this important functional group is rare in the Central Arctic Ocean. The diazotrophic community in sea-ice environments appear distinct from other cold-adapted diazotrophic communities, such as those present in the coastal Canadian Arctic, the Arctic tundra and glacial Antarctic lakes. Molecular fingerprinting of nifH and the intergenic spacer region of the rRNA operon revealed differences between the communities from river-influenced Laptev Sea waters and those from ice-related environments pointing towards a marine origin for sea-ice diazotrophs. Our results provide the first record of diazotrophs in the Central Arctic and suggest that microbial nitrogen fixation may occur north of 77ºN. To assess the significance of nitrogen fixation for the nitrogen budget of the Arctic Ocean and to identify the active nitrogen fixers, further biogeochemical and molecular biological studies are needed

Proceedings in Marine Biology

“Proceedings in Marine Biology” is an international journal publishing original research by graduate students on all aspects of marine biology. Subjects covered include: ecological surveys and population studies of oceanic, coastal and shore communities; physiology and experimental biology; taxonomy, morphology and life history of marine animals and plants. Papers are also published on techniques em - ployed at sea for sampling, recording, capture and observation of marine organisms.Zeitschrift zur Kursabschlussreise der Humboldt-Universität zu Berlin (Deutschland) im Bereich Elektronenmikroskopie.Peer Reviewe

Long-Term Summertime Investigations of Pelagic and Benthic Realms with Continuous Observations of Vertical Particle Flux in the Fram Strait and the Central Arctic Ocean

Sea ice volume and extent currently experience massive reduction in the Arctic Ocean due to climate change. Our long-term study aims at tracing effects of environmental changes in pelagic and benthic systems and investigate accompanying impacts on the fate of organic matter produced in the upper water column on its way down to the seafloor. Since the start of our observations in 1999, we have already seen some effects and will present selected data sets from the upper water column and benthic data during summer expeditions as well as results from vertical particle flux measurements that were obtained from annually deployed sediment traps at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in the eastern Fram Strait (79°/4°E) and on fewer occasions in the central Arctic Ocean (CAO). Highest biomass was found in the eastern Fram Strait and lowest in the heavily ice-covered regions in the CAO. Flux rates of POC where at least one order of magnitude lower in the CAO than in the eastern Fram Strait. While in the CAO ice algae dominate the recognizable flux fraction, faecal material prevailed in eastern Fram Strait traps. This points towards different systems of organic matter production and modification and, thus, different mechanisms determine the efficiency of the biological carbon pump. These differences are also reflected in the benthic communities in the CAO and in the eastern Fram Strait. These first results have shown the importance of long-term observations and encouraged the continuation of the Arctic Ocean Observing System FRAM (FRontiers in Arctic marine Monitoring) to record environmental and biological data at high temporal and spatial resolution