Abundance of the multiheme c-type cytochrome OmcB increases in outer biofilm layers of electrode-grown Geobacter sulfurreducens

PLoS One. 2014 Aug 4;9(8):e104336. doi: 10.1371/journal.pone.0104336. eCollection 2014.

Abstract

When Geobacter sulfurreducens utilizes an electrode as its electron acceptor, cells embed themselves in a conductive biofilm tens of microns thick. While environmental conditions such as pH or redox potential have been shown to change close to the electrode, less is known about the response of G. sulfurreducens to growth in this biofilm environment. To investigate whether respiratory protein abundance varies with distance from the electrode, antibodies against an outer membrane multiheme cytochrome (OmcB) and cytoplasmic acetate kinase (AckA) were used to determine protein localization in slices spanning ∼25 µm-thick G. sulfurreducens biofilms growing on polished electrodes poised at +0.24 V (vs. Standard Hydrogen Electrode). Slices were immunogold labeled post-fixing, imaged via transmission electron microscopy, and digitally reassembled to create continuous images allowing subcellular location and abundance per cell to be quantified across an entire biofilm. OmcB was predominantly localized on cell membranes, and 3.6-fold more OmcB was detected on cells 10-20 µm distant from the electrode surface compared to inner layers (0-10 µm). In contrast, acetate kinase remained constant throughout the biofilm, and was always associated with the cell interior. This method for detecting proteins in intact conductive biofilms supports a model where the utilization of redox proteins changes with depth.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Bacterial Outer Membrane Proteins / chemistry
  • Bacterial Outer Membrane Proteins / genetics
  • Bacterial Outer Membrane Proteins / isolation & purification*
  • Bioelectric Energy Sources
  • Biofilms / growth & development*
  • Electrodes
  • Electron Transport*
  • Geobacter / genetics*
  • Oxidation-Reduction

Substances

  • Bacterial Outer Membrane Proteins
  • OmcB protein, bacteria

Grants and funding

This work was supported by the following funding sources: the National Science Foundation, which funded The Center for Environmental Kinetics Analysis under Grant No. CHE-0431328 (S.L.B., C.S.S.) (www.nsf.gov); Alfred P. Sloan Foundation Graduate Scholarship program (C.S.S.) (http://sloanphds.org/sloan/Sloan.aspx?pageid=30); U.S. Department of Energy under Grant No. DE-SC0007058 (M.T.) (http://energy.gov/); The Office of Naval Research under Grant No. N000140810162 (E.V.L.) (www.onr.navy.mil); and U.S. Department of Energy, Office of Science (Biological and Environmental Research) under Grant No. DE-SC0006868 (D.R.B.) (http://science.energy.gov/ber/). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.