Bacterial communities associated with jellyfish

Abstract

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.