Gärtner, Andrea (2011) Isolation and characterization of bacteria from the deep-sea and their potential to produce bioactive natural products. (PhD/ Doctoral thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 144 pp.

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Abstract

Due to the high re-discovery rate of already known active compounds in recent drug research it appears reasonable to expand the search on unexplored environments with unique living conditions and yet undiscovered organisms. The deep sea demonstrates such a marginally investigated environment harboring presumably undiscovered bacterial taxa which are adapted to the extreme living conditions in the deep sea environment and which might possess unknown metabolites. The aim of the present thesis was therefore the characterization of deep-sea bacteria with the purpose to find novel and bioactive substances produced by these bacteria. Heterotrophic mesophilic bacterial strains were recovered and phylogenetically characterized from two totally different deep-sea habitats: the extremely oligotrophic Eastern Mediterranean and the Logatchev hydrothermal vent field (LHF) located at 15°N along the Mid Atlantic Ridge. The antimicrobially active bacteria isolated from the hydrothermal environments were mainly assigned to the Gammaproteobacteria. One bioactive strain, M41T, revealed to be a representative of a novel genus and species, Amphritea atlanticaT. This strain was isolated from a mussel field at LHF and physiological analysis showed that it is well adapted to the mesophilic temperatures of hydrothermally influenced environments. In addition, the bacterial community of diffusive fluids emanating out of a mussel field at LHF was investigated. A 16S rRNA gene library was analyzed in combination with functional genes involved in biochemical pathways of CO2 fixation (aclB, cbbM, cbbL) and sulfur oxidation/reduction (soxB, aprA). It turned out, that Epsilonproteobacteria and Gammaproteobacteria comprise a considerable part of the microbial community in diffuse fluids and have the genetic potential to use different pathways for carbon fixation and sulfur oxidation. The bacterial strains obtained from the Eastern Mediterranean deep sea were also analyzed for specifically adapted bacterial strains and antimicrobial activities. Predominantly Gram-positive strains were isolated from the untreated sediment, while incubation of sediment at in situ pressure revealed that Gammaproteobacteria were enriched at the simulated deep-sea conditions. Bacterial strains affiliating to the genus Micromonospora were selected for further analysis in order to investigate their potential to produce bioactive substances. This led to the discovery and structure elucidation of the novel cytotoxic macrolide levantilide A and a derivative thereof, levantilide B, both of which are produced by a deep-sea Micromonospora strain, strain A77. Thus, the results of the present study demonstrate that deep-sea habitats are a promising source for novel bacterial taxa and for the discovery of new natural products as well.

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