Synergistic iron reduction and citrate dissimilation by Shewanella alga and Aeromonas veronii
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© Springer-Verlag 1996
O R I G I N A L PA P E R
Victoria Knight · Frank Caccavo · Steve Wudyka · Richard Blakemore
Synergistic iron reduction and citrate dissimilation by Shewanella alga and Aeromonas veronii
Received: 11 December 1995 / Accepted: 19 June 1996
Abstract Two bacterial isolates from Great Bay Estuary, New Hampshire, in co-culture carried out anaerobic dissimilation of citric acid with Fe(III) as the terminal electron acceptor. Neither isolate oxidized citrate with Fe(III) anaerobically in axenic culture. The Fe(III) reducer, Shewanella alga strain BrY, did not grow anaerobically with citrate as an energy source. The citrate utilizer, Aeromonas veronii, did not reduce iron axenically with a variety of electron donors including citrate. The onset of iron reduction by the co-culture occurred after initiation of citrate dissimilation and just prior to initiation of growth by either organism (as measured by viable plate counts). Anaerobic culture growth rates and final cell densities of each bacterial strain were greater in co-culture than in axenic cultures. By 48 h of growth, the co-culture had consumed 27 mM citrate as compared with 12 mM dissimilated by the axenic culture of A. veronii. By 48 h the coculture produced half as much formate (6 mM) and twice as much acetate (40 mM) as did A. veronii grown axenically (12 mM and 20 mM, respectively). Formate produced from citrate by A. veronii appeared to have supported growth and Fe(III) reduction by S. alga.Although not obligatory, nutrient coupling between these two organisms illustrates that fermentative (A. veronii-type) organisms can convert organic compounds such as citrate to those used as substrates by dissimilatory Fe(III) reducers, including S. alga. This synergism broadens the range of substrates available for iron reduction, stimulates the extent and rate of organic electron donor degradation (and that of iron reduction) and enhances the growth of each participant.
V. Knight · S. Wudyka · R. Blakemore (Y) Department of Microbiology, University of New Hampshire, Durham, NH 03824, USA Fax +1-603-862-2621 e-mail: [email protected] F. Caccavo Center for Biofilm Engineering, Montana State University, Bozeman, MT 59717, USA
Key words Iron reduction · Citrate degradation · Synergistic association · Shewanella alga · Aeromonas Abbreviations SWC Seawater complete · ASW Artificial seawater · PBS Phosphate-buffered saline · DCIP Dichlorophenolindophenol · FDH Formate dehydrogenase
Introduction Dissimilatory iron reduction is an important means by which some bacteria participate in anaerobic carbon cycling (Ghiorse 1988; Lovley 1993; Nealson and Saffarini 1994). Microbial Fe(III) reduction may be a significant global process in that dissimilatory iron reduction can, under some conditions, outcompete sulfate reduction as a means of anaerobic organic matter mineralization (Obuekwe and Westlake 1982; Sørensen 1982; Lovley and Phillips 1987). The organisms participating in dissimilatory iron reduction are not fully known, and although most studies to da
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