Cable bacteria conduct protons over 100 micrometers, hinting at bioelectronic potential

Date:


Atomic force microscopy image of cable bacteria showing characteristic ridge structures on the surface of adjacent cells. Credit: Woo K. Lee

U.S. Naval Research Laboratory and Aarhus University, Denmark, researchers have confirmed protonic conductivity over distances exceeding 100 micrometers along filamentous Desulfobulbaceae, commonly referred to as cable bacteria. Findings provide insights into microbial proton transport mechanisms and open pathways for applications in bioelectronics.

Electrical conduits in sediment enable microbes to transfer electrons over centimeter-scale distances. Observations suggest that cable bacteria can drive local chemical shifts in sediment by coupling the oxidation of sulfur to oxygen reduction, thus modifying pH gradients.

Documented effects include acidification in deeper layers and more alkaline conditions near sediment-water interfaces. Whether this localized activity translates into broader environmental impacts is still unclear. Insights into these mechanisms may serve broader studies of microbial communication and bioprotonic device design, leading to a better grasp of natural energy flows in sedimentary environments.

Protonic conductivity has been observed in a broad spectrum of biotic materials. Measuring protonic conductivity across the exterior of bacterial cells remains elusive because bacteria placed over protodes (the proton-carrying equivalent of an electrode) tend to demonstrate poor and inconsistent contact.

In applications that have attempted to build biological-based computing, conventional semiconductor processing techniques run into the limitations of biological materials’ sensitivity to high temperature, organic solvents, high vacuum, and UV radiation.

In the study, “Hydrated cable bacteria exhibit protonic conductivity over long distances,” published in the Proceedings of the National Academy of Sciences, researchers implemented a modified transfer-printing technique to measure proton conductivity, addressing challenges such as the fragile nature of bacterial cells and inconsistent electrode contact.

Palladium-interdigitated protodes and other electrodes were adhered to non-living cable bacteria samples. Measurements were conducted under controlled conditions of temperature and humidity.

Tests involving deuterium gas (D2), which replaces protons with slower-moving deuterium ions, showed reduced conductivity, supporting the role of proton transport via the Grotthuss mechanism.

This process relies on the exchange of hydrogen bonds in water molecules forming continuous proton pathways on the bacterial surface where the proton hops through the H-bond network formed between water molecules (H2O) and hydronium ions (H3O+).

A custom-built environmental chamber with linear sweep voltammetry allowed precise adjustments to relative humidity (RH), with humidified hydrogen (H2) gas providing protons for conductivity testing. To distinguish between protonic and electronic conductivity, gold electrodes (which block proton flow) were used as controls.

Results confirmed that protonic conductivity varied with humidity levels, showing a 26-fold increase between 60% and 80% RH. Conductivity peaked at 114 ± 28 µS cm-1 at 70% RH and 25°C, supporting the hypothesis that proton transport occurs through water-associated proton wires via the Grotthuss mechanism.

Comparative studies with non-conductive filamentous bacteria, such as Microcoleus, confirmed that the observed conductivity was intrinsic to cable bacteria and not a result of water alone forming continuous Grotthuss mechanism scaffolds.

Researchers also assessed the contact resistance and specific resistivity between bacterial surfaces and electrodes. While the protonic conductivity of cable bacteria was lower than synthetic microwires, the results revealed the potential for microbial interfaces in bioelectronics.

While the evolutionary or ecological significance of protonic conductivity in cable bacteria and its potential role in interspecies interactions has yet to be fully defined, the authors suggest that protonic conductivity may influence microbial interactions and environmental proton transport. Findings set the stage for future investigations of cable bacteria within microbial communities.

More information:
Bradley G. Lusk et al, Hydrated cable bacteria exhibit protonic conductivity over long distances, Proceedings of the National Academy of Sciences (2025). DOI: 10.1073/pnas.2416008122

© 2025 Science X Network

Citation:
Cable bacteria conduct protons over 100 micrometers, hinting at bioelectronic potential (2025, January 20)
retrieved 20 January 2025
from https://phys.org/news/2025-01-cable-bacteria-protons-micrometers-hinting.html

This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no
part may be reproduced without the written permission. The content is provided for information purposes only.



Share post:

Subscribe

Popular

More like this
Related

How Alcohol Affects Your Gut

If you have gut problems, alcohol might be...

Potato Battery Experiment: How-To Plus Free Worksheet

This Potato Battery Experiment is a fun way...

Rainbow Walking Water Experiment: How-To Plus Free Worksheet

The Rainbow Walking Water Experiment is such a...