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Photomixotrophic growth of Rhodobacter capsulatus SB1003 on ferrous iron

Authors

  • S. H. KOPF,

    1. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
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  • D. K. NEWMAN

    1. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
    2. Division of Biological Sciences, California Institute of Technology, Pasadena, CA, USA
    3. Howard Hughes Medical Institute, Pasadena, CA, USA
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Corresponding author: D. K. Newman. Tel.: +1 626 395 3543; fax: +1 626 395 4135; e-mail: dkn@caltech.edu

Abstract

This study investigates the role iron oxidation plays in the purple non-sulfur bacterium Rhodobacter capsulatus SB1003. This organism is unable to grow photoautotrophically on unchelated ferrous iron [Fe(II)] despite its ability to oxidize chelated Fe(II). This apparent paradox was partly resolved by the discovery that SB1003 can grow photoheterotrophically on the photochemical breakdown products of certain ferric iron–ligand complexes, yet whether it could concomitantly benefit from the oxidation of Fe(II) to fix CO2 was unknown. Here, we examine carbon fixation by stable isotope labeling of the inorganic carbon pool in cultures growing phototrophically on acetate with and without Fe(II). We show that R. capsulatus SB1003, an organism formally thought incapable of phototrophic growth on Fe(II), can actually harness the reducing power of this substrate and grow photomixotrophically, deriving carbon both from organic sources and from fixation of inorganic carbon. This suggests the possibility of a wider occurrence of photoferrotrophy than previously assumed.

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