Evidence for rapid microscale bacterial redox cycling of iron in circumneutral environments.
The potential for microscale bacterial Fe redox cycling was investigated in microcosms containing ferrihydrite-coated sand and a coculture of a lithotrophic Fe(II)-oxidizing bacterium (strain TW2) and a dissimilatory Fe(III)-reducing bacterium (Shewanella alga strain BrY). The Fe(II)-oxidizing organism was isolated from freshwater wetland surface sediments which are characterized by steep gradients of dissolved 02 and high concentrations of dissolved and solid-phase Fe(II) within mm of the sediment-water interface, and which support comparable numbers (10(5)-10(6) mL(-1)) of culturable Fe(II)-oxidizing and Fe(III)-reducing reducing. The coculture systems showed minimal Fe(III) oxide accumulation at the sand-water interface, despite intensive O2 input from the atmosphere and measurable dissolved O2 to a depth of 2 mm below the sand-water interface. In contrast, a distinct layer of oxide precipitates formed in systems containing Fe(IllI)-reducing bacteria alone. Examination of materials from the cocultures by fluorescence in situ hybridization indicated close physical juxtapositioning of Fe(II)-oxidizing and Fe(III)-reducing bacteria in the upper few mm of sand. Our results indicate that Fe(II)-oxidizing bacteria have the potential to enhance the coupling of Fe(II) oxidation and Fe(III) reduction at redox interfaces, thereby promoting rapid microscale cycling of Fe.
Sobolev
Dmitri
D
Department of Biological Sciences, The University of Alabama, Tuscaloosa 35487-0206, USA.
Roden
Eric E
EE
D000332:Aerobiosis; D000693:Anaerobiosis; D003470:Culture Media; D017753:Ecosystem; D005290:Ferric Compounds; D005296:Ferrous Compounds / Q000378:metabolism; D005618:Fresh Water / Q000382:microbiology; D019015:Geologic Sediments / Q000382:microbiology; D006091:Gram-Negative Chemolithotrophic Bacteria / Q000254:growth & development* / Q000378:metabolism*; D007501:Iron / Q000378:metabolism*; D010084:Oxidation-Reduction; D020592:Shewanella / Q000254:growth & development* / Q000378:metabolism*; D013997:Time Factors
D003470:Culture Media; D005290:Ferric Compounds; D005296:Ferrous Compounds; D007501:Iron