TP4

Project TP4: Diversity studies and ecosystem monitoring at the model habitat “Gotland deep”, Baltic sea

Responsible: Klaus Jürgens and Matthias Labrenz, IOW

 

The subproject TP4 is focused on pelagic redoxclines located in the central Baltic Sea (Fig.1A). As a comparably flat “estuary” brackish sea with limited water supply from the Atlantic, the deeper Baltic Sea water layers are usually anoxic and thus establish redoxclines, with a chemocline as the first appearance of sulfide. With increasing depths concentrations of oxidized substances as molecular oxygen or nitrogen decrease to a minimum within such redoxclines, whereas reduced substances accumulate with further increasing depths. Such areas are usually established at depths ranging from 100-120 m. Due to the anthropogenic impact (agriculture, climate change) these areas, which exclude higher life forms, grow. This is a reason why they are of general interest for the local population, but can additionally be regarded as a model system for other marine ecosystems being in flux. From sulfidic to suboxic zones, but especially in the anaerobic areas, bacterial dark CO2-fixation occurs (Fig. 1B), dominated by chemolithoautotrophic Epsilonproteobacteria of the Sulfurimonas GD17-cluster - including its most numerous representative strain GD1. 

 

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Standard sampling procedures combine the harvest of bacteria from their environment via Niskin bottles or pumps with simultaneous measurements of conductivity, temperature, and depth. Other analyses follow, e.g. chemical profiling or cell preparation tailored to the particular needs of the scientific question and the adjacent experiments. The sampling procedures are permanently adapted and developed further to assure results of highest quality (analog to TP3). Further details about sampling procedures can be found at the IOW-homepage, particularly e.g. 

http://www.io-warnemuende.de/mit-uns-auf-see.html,     

http://www.io-warnemuende.de/kurzbericht-2802---1603.html.

To establish a bacterial model organism for such redoxclines we isolated the chemolithoautotrophic Sulfurimonas strain GD1 from the Gotland Deep, initiated the sequencing of its genome (funded by the Gordon & Betty Moore Foundation), and cultivated the bacterium on different ecologically relevant substrates characteristic for pelagic Baltic Sea redoxclines. We found this bacterium to be metabolically highly versatile by culture based studies as well as by genome analyses, revealing encodings of key enzymes for various metabolic pathways.

Since GD1 is very abundant in different water layers around Baltic Sea redoxclines characterized by different redox conditions, we suspect this bacterium to be highly metabolically adaptive, not only in axenic cultures but in nature as well. The overall abundance of these cells led to the concept to collect proteins from environmental samples from significant points near the chemoclines and to investigate these metaproteoms (TP1) in comparison to chemical profiles from these sampling sites. DNA (TP3) and/or RNA (analog to TP2) extracted from the same samples are sequenced by 454 pyrosequencing (TP5) to serve as a basis for mass-spectrometric peptide mapping. In addition, we can luckily compare these findings to culture based overall proteome (TP1) and transcriptome analyzes when simulating different ecological relevant conditions as well as climate influences. Soluble and membrane associated GD1 proteins are separated, either by gel based methods (Fig.2) or by liquid chromatography, and subsequently identified by mass-spectrometric analyzes (TP1). GD1 transcripts regulated within individual cultivation modi are selectively purged by subtractive hybridization and identified (TP5).

 

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By linking this way in situ and in vitro proteomes, transcriptomes, and related chemical datasets we plan to elucidate the ecological role of GD1 within its habitat, thus mapping and correlating the main metabolic processes at the redoxclines, and to establish this way a basis for future sensitive environmental monitoring in the Baltic Sea (Fig.3). 

 

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We want to stress finally that marine habitats are still poorly understood, although marine environments are the largest ecosystem on earth. Since only ~ 0.1 percent of marine microbes are cultivable, concepts about the role of microorganisms in these environments regarding major geochemical cycles are in their initial stage. Therefore the development of new cultivation independent complex high-resolution monitoring techniques is mandatory.