Formation of Cell-Iron-Mineral Aggregates by Phototrophic and Nitrate-Reducing Anaerobic Fe(II)-Oxidizing Bacteria

Microbial anaerobic Fe(II) oxidation at neutral pH produces poorly soluble Fe(III) which is expected to bind to cell surfaces causing cell encrustation and potentially impeding cell metabolism. The challenge for Fe(II)-oxidizing prokaryotes therefore is to avoid encrustation with Fe(III). Using different microscopic techniques we tracked Fe(III) minerals at the cell surface and within cells of phylogenetically distinct phototrophic and nitrate-reducing Fe(II)-oxidizing bacteria. While some strains successfully prevented encrustation others precipitated Fe(III) minerals at the cell surface and in the periplasm. Our results indicate differences in the cellular mechanisms of Fe(II) oxidation, transport of Fe(II)/Fe(III) ions, and Fe(III) mineral precipitation.