Shocks to Bacteria Boost a Living Power Grid

Nanoscale characterization with multiple AFM modes showed that in electric fields, biofilms of Geobacter sulfurreducens bacteria produced protein nanowires with much higher electrical conductivity and stiffness. The effect was further enhanced by acidic environments.

(top) Topography images of OmcZ nanowires and line section across the red line; (bottom left) conceptual drawing of bacteria, OmcZ nanowires, and electron transport in an electric field; (bottom right) histograms of OmcS and OmcZ nanowire diameter at pH 2 and pH 7 as measured from topography images. Living materials with electronic functionality could create a new paradigm of self-replicating, biocompatible electronics. Yet in the few biological systems known to transport charge, the conduction mechanism remains a mystery.

Yale University researchers investigated this topic using Geobacter sulfurreducens, a common soil bacterium. Previous work showed these bacteria use conductive nanowires of a protein called OmcS to remove excess electrons in a respiration process. In contrast, the current study observed that biofilms grown in an electric field produced nanowires of another protein, OmcZ.

The researchers characterized the nanowires with a suite of complementary imaging and spectroscopy tools including AFM structural, nanoelectrical, and nanomechanical modes. They found that OmcZ nanowires had 1000 times higher electrical conductivity and threefold higher stiffness than OmcS ones. Lowering the pH increased conductivity and stiffness even more, meaning the nanowires could function in acidic environments that break proteins down.

With the ability to transduce mechanical and chemical stimuli into electrical signals, the nanowires reported in these results could help bring about new kinds of durable, self-healing bioelectronics.

(top) AFM current experiments showing (left) schematic, (center) I-V curves measured at the color-coded points in the schematic, and (right) conductivity of OmcS and OmcZ nanowires at pH 2 and 7; (bottom) nanomechanical measurements showing (left) topography and modulus maps (right) and Young’s modulus for OmcS and OmcZ nanowires at pH 2 and 7.

Instrument used

Cypher ES with Dual Gain ORCA module and AM-FM Viscoelastic Mapping Mode

Techniques used

All AFM experiments were performed on a Cypher ES AFM, including topography imaging in air with tapping mode. Sub-nanometer measurements of nanowire diameter for insight into conformational changes were enabled by the exceptional spatial resolution of Cypher AFMs. The electrical conductivity was determined by acquiring current-voltage (I-V) curves at selected positions along the nanowires. These measurements used conductive AFM (CAFM) techniques with a Dual Gain ORCA module, which contains two separate amplifiers for sensitive, low-noise current measurements over a very wide current range (~1 pA to 10 µA). Young’s modulus of the nanowires was imaged in AM-FM Viscoelastic Mapping Mode. Exclusive to Asylum Research, AM-FM is a bimodal AFM technique that allows extremely gentle modulus mapping at the fast acquisition speeds of tapping mod

Citation: S. Yalcin, J. O’Brien, Y. Gu et al., Electric field stimulates production of highly conductive microbial OmcZ nanowires. Nat. Chem. Biol. 16, 1136 (2020). https://doi.org/10.1038/s41589-020-0623-9

Note: The data shown here are reused under fair use from the original article, which can be accessed through the article link above.