Combined Spectroscopic and Topographic Characterization of Nanoscale Domains and Their Distributions of a Redox Protein on Bacterial Cell Surfaces

Abstract

Redox protein nanoscale domains on the cell surface of a bacterium, Shewanella oneidensis MR1, grown in the absence and presence of electron acceptors, is topographically characterized using combined atomic force microscopy (AFM) and confocal surface enhanced Raman scattering (SERS) spectroscopy. The protruding nanoscale domains on the outer membrane of S. oneidensis were observed, as was their disappearance upon exposure to electron acceptors such as oxygen, nitrate, fumarate, and iron nitrilotriacetate (FeNTA). Using SERS spectroscopy, a redox heme protein was identified as a major component of the cell surface domains. This conclusion was further confirmed by the disappearance of Raman vibrational frequencies, characteristic of heme proteins, upon exposure of the cells to electron acceptors. Our experimental results from our AFM imaging and SERS spectroscopy, consistent with the literature, suggest the protruding nanoscale surface domains as heme-containing secretions. Our results on the distributions of redox proteins on microbial cell surfaces will be helpful for a mechanistic understanding of the behaviors of surface proteins and their interactions with redox environments.

Surface multiheme c -type cytochromes from Thermincola potens and implications for respiratory metal reduction by Gram-positive bacteria

“…S2) (26). This process is termed SERS, and has served to visualize cell-surface Raman active species in several bacteria (19,(27)(28)(29). The SERS effect decays exponentially within a few nanometers from the metal surface, but the enhancements can be as -fold (26).…”

Vibrational spectroscopic mapping and imaging of tissues and cells

“…For example, Raman microprobe fibre optics have been combined with many other techniques (Aitken et al 2009;Williams et al 2003) including AFM (Biju et al 2007;Eronen et al 2009), microdiffraction (Davies et al 2009) and scanning electron microscopy (SEM), which is interfaced with the Raman spectrometer via a structural chemical analyzer allowing elemental and chemical information to be obtained from the same area of the same sample (Williams et al 2003).…”

C‐Type Cytochromes Wire Electricity‐Producing Bacteria to Electrodes

“…[13] It is recognized that in spite of the complexity of the bacterial surface this technique allows the selective resolution of bacterial molecules (or molecular domains) in direct contact with the electrode with high specificity (Scheme 1). [12] As a matter of comparison, the evanescent field is notably thinner than the protruding redox domains (18-25 nm) previously detected on the surface of another electrogenic bacteria such as Shewanella oneidensis, [14] and suggested to be heme-containing proteins. The interaction of G. sulfurreducens cells with a gold electrode polarized at 0.2 V (vs. Ag/AgCl-NaCl 3 m) produces an electric current that increases with time ( Figure 1 a), demonstrating that a gold electrode can act as electron acceptor for these bacteria.…”