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Chapter 101 : Microbial Fe(III) Reduction: Ecological and Physiological Considerations
The dissimilatory Fe(III)-reducing bacteria (FeRB) are anaerobic prokaryotes that couple the oxidation of an electron donor such as hydrogen or short-chain fatty acids such as acetate to the reduction of Fe(III) as an energy-conserving metabolic process. The researchers pumped an anaerobic medium mixed with a green fluorescent protein-expressing strain of Shewanella oneidensis through the aerobic flow cell (AFC) and across the mineral surface. Surface pitting from mineral dissolution was heterogeneous, as was the precipitation of secondary Fe(II) minerals. These studies highlight the importance of considering the effects of open systems on the physiology and biogeochemistry of iron-microbe interactions. The geochemistry of the environment under study can provide the first indications of microbial Fe(III) reduction. Most 16S rRNA-based molecular ecology tools can be, and have been, applied to the FeRB. The volume of literature focusing on the biochemistry and physiology of FeRB has increased dramatically in the last 3 years. Based on numerous studies, it is clear that with all FeRB studied, there are two common themes shared by all of these organisms. The first is that cell attachment to mineral surfaces is common in all FeRB studied and is probably essential to Fe(III) reduction. The second theme is the abundance of c-type cytochromes in almost every organism studied.
Stainless steel biofilm coupon with fragments of specular hematite ( 90 ). Inset, DAPI (4′, 6′, diamidino-2-phenylindole)-stained biofilm formed on the surface of a hematite particle after incubation in groundwater. Images courtesy of Brent Peyton (Montana State University) and Katie Reardon (Pacific Northwest National Laboratory).
In situ interrogation of biofilms of G. sulfurreducens. The scale bar is 10 μm in both panels. Note the intimate association of cells with mineral particles (M) in both images. (A). In situ RT-PCR of G. sulfurreducens grown on ferrihydrite. The gene target was omc C, which encodes a cytochrome c. Mineral particles are outlined, and cells expressing the gene are in brightly fluorescent groups. (B) Combined fluorescence and phase-contrast image of G. sulfurreducens grown on ferrihydrite. Cells were stained with DAPI (pink) and a fluorescent lectin EPS probe (green).