Research in our laboratory aims at an understanding of microbial activities in nature, the limits and principles of substrate turnover and energy exploitation. At present, we concentrate mainly on anaerobic bacterial transformations, but have recently expanded also into microaerobic environments, focussing especially on oxic-anoxic interfaces.

Main Research Areas 

Redox processes in lake sediments
In littoral sediment of Lake Constance, iron oxides are an important constituent of the insoluble mineral phase and contribute substantially to redox processes in the sediment. We are interested in the biochemical mechanism of ferric oxide reduction, of anaerobic reoxidation of ferrous iron under the influence of light and nitrate, and in the dynamics of these processes and their interference with the sulfur cycle. We are also looking for microaerobic methane oxidation as a key process of oxygen consumption in the anoxic-oxic transition phase.

Energetics of anaerobic degradation processes
Microbial life in the absence of oxygen has to operate with substantially smaller energy budgets than aerobic life. At the very end, the conversion of biomass to methane and CO₂ yields only 15 % of the energy available to aerobic oxidation, and this small amount has to be shared by 3 – 4 trophic groups (guilds) of functionally different bacteria. In the last steps of methanogenic fermentation processes, every single organism has less than 1 ATP equivalent available to its energy metabolism. We try to understand microbial energy metabolism with such small energy increments as model systems to define the energetic limits of life in general. These studies are of key importance to understand the mechanisms of survival of huge amounts of prokaryotes in deep sediments. Our studies also help to improve the production of methane (“biogas”) from waste materials.

Biochemistry of anaerobic degradation of comparably stable compounds
The degradation of natural and synthetic substrates in anoxic environments such as sediments cannot employ oxygen in the activation of comparably stable compounds such as aromatic compounds, hydrocarbons or polyethers (e.g. lignin). Degradation of such compounds in the absence of oxygen has to employ basically different biochemical strategies than in the presence of oxygen. Primary substrate activation reactions include reductive destabilizations, oxygen-independent hydroxylations via molybdenum enzymes, carboxylations, and radical-catalyzed rearrangements of carbon skeletons. In some cases, e.g., with the bifunctional phenol resorcinol, even two different strategies of anaerobic degradation were observed, depending on whether nitrate is available as an alternative electron acceptor or not. We try to understand the biochemical strategies of substrate degradation in the absence of oxygen in order to analyze the limits of anaerobic biodegradation capacities in general. The results help to define the limitations of biomass utilization in the production of microbial energy feedstocks (ethanol, biogas) for mankind, or in the development of biodegradable polymers, e.g., in the packaging industry.

Bacteria-zooplankton interaction
We chose an important small invertebrate active in the food chain in the lake water column to study the interaction between the host and its gut microbiota.