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

Abstract

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.

Keywords:

• Fe(II) oxidation
• iron-cycling
• geomicrobiology

Present affiliation for K. L. Straub is Department of Environmental Geosciences, University of Vienna, Austria. This work was supported by an Emmy-Noether fellowship and several research grants from the German Research Foundation (DFG) to Andreas Kappler and a BMBF research grant (13N8652) to the Natural and Medical Sciences Institute at the University of Tuebingen. Some of the TEM images were taken by R. Mielke during a DFG-funded postdoctoral fellowship of AK in the laboratory of Prof. Dianne Newman at the California Institute of Technology. We would like to thank N.R. Posth and P. Larese-Casanova for their helpful comments in improving the manuscript. We thank Stephan Borensztajn from Laboratoire Interfaces et Systemes electrochimiques, UPR 15 CNRS, for SEM imaging. KB and JM are also grateful to Region Ile-de-France for the SESAME 2000 E1435 grant for the acquisition of the JEOL 2100F TEM at IMPMC UMR 7590.