Gerdts, Gunnar
Lade...
3 Ergebnisse
Gerade angezeigt 1 - 3 von 3
- Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Bacterial communities associated with jellyfish(2014-02-27); ; ; This thesis represents the first investigation to understand the bacterial community associated with jellyfish, with special emphasis on ctenophores and scyphomedusae, at Helgoland Roads in the German Bight (North Sea, Germany). Bacterial communities associated with the frequently occurring ctenophore species Mnemiopsis leidyi, Beroe sp., Bolinopsis infundibulum and Pleurobrachia pileus were investigated. Species-specific differences regarding the different ctenophores were revealed in the present study. The bacterial communities of all ctenophore species were dominated by Proteobacteria as revealed by pyrosequencing. The predominant groups associated with ctenophores are Marinomonas, Thalassospira, Pseudoalteromonas and Psychrobacter. Regarding the typical metagenetic life cycle of scyphomedusae, the bacterial communities associated with two scyphomedusae species (Cyanea lamarckii and Chrysaora hysoscella) were firstly investigated at Helgoland Roads. Two aspects were studied: different body parts and different life stages. Significant differences were revealed between umbrella and other body parts (gonad and tentacle) in terms of the associated bacterial community in both species. With regard to the different life stages, bacterial community structure varied from the early stage planula larvae to polyps even to adult medusae with significant differences in both species with completely distinct patterns. Furthermore, the impact of the food source on the associated bacterial community was investigated with respect to polyps. Bacterial communities associated with polyps were significantly distinct from the food in both species. Polyps might react differently during metabolic processing in response to different food source (A. salina and plankton) resulting in a significantly different bacterial community structure. In general, the bacterial communities associated with two scyphomedusae species are species-specific as confirmed in each life stage. The utilization of DOM released by live jellyfish was firstly investigated in the third part of this thesis. We focused on the compositional succession of bacterioplankton community in response to the DOM released by live scyphomedusae (Cyanea lamarckii and Chrysaora hysoscella). Bacterial community structure was determined via Automated Ribosomal Intergenic Spacer Analysis (ARISA) fingerprints at the end of the experiments. Catalyzed reporter deposition fluorescence in situ hybridization (CARD-FISH) analysis was applied to reveal the bacterial community composition at different time points. The bacterial community was significantly stimulated by the DOM released by live jellyfish with different dominant phylotypes regarding to different scyphomedusae species based on CARD-FISH analysis. The significant differences in the bacterial community composition and succession indicate that the DOM released by jellyfish might consist of different compounds which are species specific. Last but not the least, DOM released by live jellyfish strongly impacted the natural bacterioplankton community not only on the bacterial abundance, but also on the community composition.Dissertation290 82 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Spatiotemporal dynamics of the bacterial community in the German Bight(2015-11-06); ; ; Microbes comprise the most abundant and diverse group of organisms on earth, contribute substantially to every conceivable biogeochemical cycle and thus, are fundamental to ecosystem functioning. Research on marine microbial communities has proven the existence of biogeographic patterns, but the mechanisms that shape the microbial assemblages are still not understood properly, as most of the studies revealed different driving forces for different temporal and spatial scales and individual habitats. However, to predict and estimate potential ecological impacts that arise from microbial community variation, it is of utmost importance to unveil the mechanisms that are generating and maintaining community assembly. This thesis aimed at providing detailed insight into the spatiotemporal variation of bacterioplankton communities in the German Bight, to deconvolute spatial and temporal signals and to identify the main regulating forces driving these dynamics.Dissertation292 127 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Distribution and Function of marine Bacteroidetes(2014-03-27); ; ; Members of the phylum Bacteroidetes play a pivotal role in degrading organic matter and appear everywhere in marine and freshwater systems, from coastal to open ocean, from polar to equatorial, from surface waters down to the deep sea as well as in association with aggregates and with phytoplankton blooms. The studies described in this thesis elaborate on the distribution and function of marine Bacteroidetes. Specifically their association with spring phytoplankton blooms, substrate association by direct surface attachment and their genetic capability of degrading high molecular weight organic matter and in particular polysaccharides were examined. The Bacteroidetes distribution and community structure were analyzed at a temporal scale, by investigating the responses of distinct bacteroidetal clades during and after spring phytoplankton blooms of four consecutive years at the coastal station Helgoland Roads. It could be shown by automated microscopic cell counting that shortly after the chlorophyll a maximum concentration Bacteroidetes increased to more than 50% of the total bacterioplankton community during spring seasons. The Bacteroidetes community comprised only a few dominant genera, which accounted together for more than half of the Bacteroidetes. Each year a distinct succession pattern of the clades Ulvibacter, Formosa A, and Polaribacter was observed with relative abundances of single clades with up to 20%. Furthermore, members of the Bacteroidetes inhabited not only the free-living fraction, but they were also found attached to diatoms. Although a quantification of attached Bacteroidetes was difficult, qualitative observations were made. For example members of this phylum attach frequently to the diatom Chaetoceros spp., which is commonly blooming in spring at Helgoland Roads. The clades Polaribacter and Formosa A were identified as dominating among those Chaetoceros-associated Bacteroidetes. In contrast, Ulvibacter was not found attached to Chaetoceros, but to Asterionella spp., another diatom genus occurring in spring blooms. Since members of Bacteroidetes are the first in responding to algal blooms and attached even to distinct diatom species, we investigated their genetic potential to degrade algal derived organic matter. In particular we searched for the presence of polysaccharide utilization loci (PULs) in fosmids retrieved from two contrasting provinces of the North Atlantic Ocean. In total 14 PULs were identified, six on fosmids from the northern station and eight on fosmids from the southern station. Among those PULs one seems to be involved in xylan degradation and four were identified as potential laminarin degradation PULs. Interestingly, GHs were identified which had been assumed to be unique among terrestrial Flavobacteria, suggesting a higher capability of open ocean Bacteroidetes clades for organic matter degradation than previously anticipated.Dissertation369 115