Fe(III) Oxide Reduction by a Gram-positive Thermophile: Physiological Mechanisms for Dissimilatory Reduction of Poorly Crystalline Fe(III) Oxide by a Thermophilic Gram-positive Bacterium Carboxydothermus ferrireducens

Abstract

Physiological strategies driving the reduction of poorly crystalline Fe(III) oxide by the thermophilic Gram-positive dissimilatory Fe(III)-reducing bacterium C. ferrireducens were evaluated. Direct cell-to-mineral contact appears to be the major physiological strategy for ferrihydrite reduction. This strategy is promoted by cell surface-associated c-type cytochromes, and the extracellular electron transfer to ferrihydrite is linked to energy generation via a membrane-bound electron transport chain. The involvement of pili-like appendages in ferrihydrite reduction has been detected for the first time in a thermophilic microorganism. A supplementary strategy for the utilization of a siderophore (DFO) in dissimilatory ferrihydrite reduction has also been characterized.

Keywords:

• dissimilatory metal reduction, iron reduction, bioavailability, aquatic sediments, thermophilic microorganisms, Gram-positive bacteria

Acknowledgments

This work was supported by grant 09-04-00251-a from the Russian Foundation for Basic Research, by programs “Molecular and Cell Biology” and “The Origin and Evolution of the Biosphere” of the Russian Academy of Sciences, and project R112045 from the Royal Society of London. We are thankful to Prof. Dr. Simon de Vries (Delft University of Technology) for his suggestion to use DFO in studies of Fe(III)-reducing activity of C. ferrireducens. We thank Drs. Vladimir V. Sorokin (Winogradsky Institute of Microbiology, RAS), John Waters and Victoria Coker (The University of Manchester) for performing scanning electron microscopy studies and X-ray analysis; Dr. Andrey L. Mulyukin (Winogradsky Institute of Microbiology) and Prof. Mathew Upton (The University of Manchester) for their help in acquaintance with live/dead staining procedure and analysis.