Microbial Iron Reduction in Marine Sediments from the Baltic Sea

The iron cycle is a key biogeochemical cycle in terrestrial and aquatic systems including marine environments. Iron is cycled in marine environments by abiotic and biotic reductive and oxidative processes. However, limited information exists about the diversity and metabolic pathways of microorganisms linked to the iron cycle in ocean sediments. The goals of my study are: 1) to determine the types of microorganisms present in marine sediments capable of iron reduction 2) determine what genes are expressed by iron reducing microorganisms in marine sediments in response to iron reduction. My hypothesis is that members of the Geobacter family of bacteria dominate ocean sediments in which iron reduction takes place and that genes associated with iron reduction include those of multiheme cytochromes. In this study, sediment samples from the upper 10 cm of marine sediments collected off the coast of Skagerrak (Baltic Sea) were used to enrich for iron reducing microorganisms in incubation experiments using a modified artificial seawater medium. In these enrichments, ferrihydrite and lepidocrocite iron oxide minerals were used as terminal electron acceptors and acetate as an electron donor. Additionally, molybdenum was included to inhibit sulfate reduction. Enrichments were incubated at 10°C for one month before iron reduction was observed. Sediments showing iron reduction were processed for DNA and RNA extraction. Currently, molecular analyses are underway to determine the identity of the iron reducing communities in these enrichments using quantitative real time PCR (qRT-PCR), cloning and sequencing techniques.