9708535 Van Cappellen A combined geochemical and microbiological approach is proposed to investigate the kinetic controls of dissimilatory iron (III) and sulfate reduction, two of the major respiratory pathways in anaerobic environments. Experiments will be performed using sediments collected in the saltmarsh of Sapelo Island, Georgia, where sulfate and iron reducing bacteria are major components of the microbial population. The co-investigators will use 16S rRNA-targeted oligonucleotide probes to detect sulfate- and Fe(III)-reducing bacteria, in conjunction with activity assays, phylogenetic screening, and kinetic flow-through reactor experiments. The molecular probes will establish the relative abundances of sulfate and iron reducing bacteria in the sediments core sections, and provide independent information to differentiate chemical and microbial pathways. The flow-through experiments on undisturbed sections of sediment cores will provide the kinetic data needed to derive rate expressions for the two dissimilatory pathways, as a function of temperature, substrate availability (organic matter, iron(III) oxyhydroxides, sulfate) and the composition of the pore solution (sulfide, nutrients, pH). The analysis of phylogenetically informative gene sequences will assess the similarity between the iron and sulfate reducing bacteria that propagate on the reactor systems and the naturally-occurring populations. This proposal was submitted in response to the Environmental Geochemistry and Biogeochemistry (EGB) solicitation, NSF 96-152. The proposed research is being jointly supported by the Divisions of Earth Sciences and Ocean Sciences.
