Team

Responsibilities

My project deals with anaerobic degradation of acetone by sulfate-reducing bacteria. Whereas mechanisms of acetone degradation are well known for aerobic and nitrate-reducing bacteria, only little is known about the mechanism used by sulfate reducers. Due to their extreme energy limitation, they could not afford such expensive activation mechanism like other bacteria. Whereas nitrate reducers use carbon dioxide for activation of acetone, sulfate reducers use carbon monoxide.

I am working on the full elucidation of this new activation mechanism. Therefore, I am using biochemical and proteomic methods as well as other analytical methods like GC and HPLC.

Responsibilities

Syntrophic acetate oxidation - investigation of NADH oxidizing enzymes in Thermacetogenium phaeum.

Responsibilities

My work is part of the Research Training Group “R3 – Responses to biotic and abiotic changes, Resilience and Reversibility of lake ecosystems”, Project C2:

Dynamics of „dark“ primary production in a changing lake environment – the role of nitrifying microorganisms

My PhD project deals with nitrification in Lake Constance, which is the only biological process linking the reduced and oxidative pools of inorganic nitrogen, and thus an important part of the nitrogen cycle. Here, I focus on ammonia oxidation, which is the rate limiting step of nitrification. Since 100 years ammonia oxidizing bacteria are known, but only twelve years ago ammonia oxidizing archaea were discovered. The latter were found to be highly abundant in marine waters, if they are also prominent in freshwater systems, concerning ammonia oxidation, is still under investigation and will be studied during my project. With the help of the functional and genetic marker gene amoA and qPCR, abundances and activities will be quantified in surface and bottom waters during the course of the year. Based on these results, metagenomic and -transcriptomic analyses will follow, to get a closer look into the genetic make-up and the metabolic activity of ammonia oxidizing archaea. As ammonia oxidizers gain their energy chemolithotrophically from the oxidation of ammonium and not from sunlight, they can thrive in the aphotic as well as in the photic zone. The contribution of nitrifying microorganisms to the overall “dark” primary production will be measured using radioactive isotope techniques. With these experiments and analyses, I want to clarify the role of ammonia oxidizing archaea in Lake Constance and their contribution to the nitrogen and carbon cycle.

Publications

Giebel HA, Klotz F, Voget S, Poehlein A, Grosser K, Andreas Teske A, Brinkhoff T (2016) Draft genome sequence of the marine Rhodobacteraceae strain O3.65, cultivated from oil-polluted seawater of the Deepwater Horizon oil spill. Stand Genomic Sci. 11:81. (DOI: 10.1186/s40793-016-0201-7)

Responsibilities

My main focus lies on understanding the biochemistry of microbial energy conservation. In particular, I currently investigate the enzymes involved in and the biochemical reactions occurring during anaerobic syntrophic degradation. Besides the syntrophic cocultures that have been long known and also studied at the Chair of Microbial Ecology, I currently also investigate novel organisms, for example a syntrophic, glucose oxidizing Bacillus strain recently isolated from lake sediment. Isolation of additional syntrophic cocultures from environmental samples to complement and extend the current knowledge about syntrophs is another aim of my research.

Responsibilities

I study microorganisms involved in the cycling of sulfur. In more detail, I am investigating the role of sulfate reducing microorganisms in the mineralization of organic matter degradation intermediates. These organisms are ubiquitous, literally breathe sulfate and are responsible for up to 50% of carbon mineralization in marine and freshwater habitats, which makes them important players in sulfur and carbon cycling. In natural environments the thereby formed product hydrogen sulfide often reacts with ferrous iron and forms iron sulfide. Over the years, iron sulfide chemically reacts to pyrite (commonly known as “fool’s gold”), which serves as a sulfur and iron sink and is part of the Earth’s crust. In our laboratory, we found evidence for biologically catalyzed pyrite formation and I aim to elucidate the identity of the responsible organisms as well as their activities and interactions.

<link file:264962>Greigite Video

<link file:264960>Greigite Negativ Kontrol

Responsibilities

I investigate the importance of sulfate-reducing microorganisms in anaerobic organic matter degradation in Lake Constance with a focus on chitin and its monomer ß-1,4-N-acetyl-D-glucosamine (GlcNAc). Chitin is the most abundant polymer in aquatic systems and can serve as carbon and nitrogen source for many microorganisms. Chitin and GlcNAc enrichment cultures were set up using Lake Constance sediment as inoculum on various temperatures with highest growth activities observed at 60°C. To investigate the influence and importance of these microorganisms under the suitable conditions, process measurements and phylogenetic analysis will be done. In addition, to obtain more information of these thermophilic Chitin and GlcNAc decomposing microorganisms, a main focus is also to isolate the chitin hydrolyzing microorganisms. To investigate chitin and GlcNAc degradation also under naturally occurring conditions, microcosms were set up in the presence and absence of periodic additions of small amounts of sulfate over a period of 50 days. Sulfate was readily turned over and accumulated only slightly towards the end of the incubations. In both the GlcNAc and the chitin microcosms, acetate was the main degradation product under sulfate-reducing as well as methanogenic conditions. However, under both substrates methanogenesis was reduced by 50-86% under sulfate-reducing conditions. The identification of microorganisms involved in chitin and GlcNAc degradation under sulfate-reducing and methanogenic conditions is anticipated by high throughput amplicon sequencing of 16S rRNA cDNA and 16S rRNA gene. All these results will contribute to a better understanding and the importance of sulfate reduction during anaerobic chitin turnover.