Iron oxidation and reduction
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.
Aerobic and nitrate-dependent oxidation of elemental sulfur
Here, we investigate the aerobic and nitrate-dependent oxidation of elemental sulfur in littoral sediment. Little is known about the activation and transport of the insoluble elemental sulfur into the cell. Known sulfur-oxidizing isolates are often not tested for the oxidation of elemental sulfur but only for utilization of soluble sulfur compounds such as sulfide, thiosulfate, or sulfite. The importance of sulfur oxidation in lake sediment is examined on the basis of most probable number counts. Numerically dominant isolates from enrichment cultures are studied with regard to the biochemistry of sulfur uptake and sulfur activation. For comparison, we also look at numbers and isolates from profundal sediment and at sequenced sulfur-oxidizing bacteria.
Bacterial pyrite formation
Pyrite (FeS2) is ubiquitous in natural sediments. According to the Wächtershäuser (1988) hypothesis, pyrite and hydrogen are formed exergonically from ferrous sulfide (FeS) and hydrogen sulfide (H2S). In enrichment cultures the formation of pyrite and greigite (Fe3S4) was observed with FeS and H2S as the only substrates (Dr. Ben Griffin). Also phototrophic bacteria are capable to utilize FeS and to produce pyrite. Therefore, we are presently running a set of growth experiments with different phototrophic bacteria. Afterwards, the steps of the pyrite formation reaction series are to be determined. Pyrite formation by phototrophic bacteria is especially of interest to draw conclusion on the evolution as well as to identify new biochemical pathways.