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arxiv: 2606.03172 · v1 · pith:EY4YLDMUnew · submitted 2026-06-02 · ⚛️ physics.chem-ph

Spin-Dependent Electron Transport through Bacterial Cell Surface Multiheme Electron Conduits

Suryakant Mishra , Sahand Pirbadian , Amit Kumar Mondal , Mohamed Y. El-Naggar , Ron Naaman This is my paper

Pith reviewed 2026-06-28 08:16 UTC · model grok-4.3

classification ⚛️ physics.chem-ph
keywords spin selectivitymultiheme cytochromesextracellular electron transferShewanella oneidensischiral induced spin selectivityelectron transportbacterial cell surfaceMtrF OmcA
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The pith

Electron transport through bacterial multiheme cytochromes on cell surfaces is spin-selective.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

Multiheme cytochromes on bacterial surfaces serve as conduits carrying electrons over distances greater than 10 nanometers from inside the cell to external minerals or electrodes. The study applies magnetic conductive probe atomic force microscopy, Hall voltage measurements, and spin-dependent electrochemistry to decaheme proteins MtrF and OmcA from Shewanella oneidensis. These techniques reveal that electron flow through the conduits favors one spin orientation. The finding extends the chiral induced spin selectivity effect to extracellular electron transfer. This spin dependence may affect how bacteria respire solid minerals and how cells connect to electrodes in engineered systems.

Core claim

Using magnetic conductive probe atomic force microscopy, Hall voltage measurements, and spin-dependent electrochemistry on the decaheme cytochromes MtrF and OmcA from Shewanella oneidensis MR-1, the paper shows that electron transport through these extracellular conduits is spin-selective.

What carries the argument

Spin selectivity arising in the multiheme cytochromes that form the long-distance extracellular electron conduits.

If this is right

  • Spin selectivity can influence electron transfer rates across biotic-abiotic interfaces in natural mineral respiration.
  • Magnetic fields may modulate the efficiency of bacterial extracellular electron transport.
  • Spin-dependent effects could be harnessed when wiring bacterial cells to electrodes in bioelectrochemical devices.
  • The same spin preference may appear in other multiheme proteins involved in long-range electron conduction.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The spin selectivity might allow bacteria to respond to weak magnetic fields in their environment during mineral respiration.
  • Engineering the heme chain geometry could tune spin selectivity for specific bioelectronic applications.
  • Similar measurements on other extracellular electron conduits would test whether spin selectivity is a general feature of multiheme proteins.

Load-bearing premise

The recorded magnetic and spin-dependent signals come specifically from spin preference inside the cytochromes and not from cell-surface structures, electrode interfaces, or other magnetic effects.

What would settle it

Repeating the magnetic probe, Hall, and electrochemistry measurements on the same cytochromes after disrupting their chiral structure or removing the heme chain while keeping other cell components intact and observing loss of the spin preference would falsify the claim.

Figures

Figures reproduced from arXiv: 2606.03172 by Amit Kumar Mondal, Mohamed Y. El-Naggar, Ron Naaman, Sahand Pirbadian, Suryakant Mishra.

Figure 2
Figure 2. Figure 2: (a) Optical microscopic image of the Hall device patterned on GaN/AlGaN substrate. (b) A scheme of the Hall device on which a monolayer of the protein is adsorbed. (c) A scheme of the setup used for measuring spin polarization. A Hall device coated with monolayer of proteins is covered by buffer electrolyte with top gate electrode insulated from the solution. (d) Spin-dependent electrochemistry setup where… view at source ↗
Figure 3
Figure 3. Figure 3: The spin polarizability measured as a function of the potential applied (dotted black line) on the top gate of gold (Fig. 2C) for (a) device coated with MtrF and (b) device coated with OmcA. (c) The Hall signal as a function of the gate voltage applied for devices coated with MtrF (red) and OmcA (blue). A linear response is observed and OmcA having higher spin polarizability compared to MtrF [PITH_FULL_IM… view at source ↗
read the original abstract

Multiheme cytochromes, located on the bacterial cell surface, function as long-distance (> 10 nm) electron conduits linking intracellular reactions to external surfaces. This extracellular electron transfer process, which allows microorganisms to gain energy by respiring solid redox-active minerals, also facilitates the wiring of cells to electrodes. While recent studies suggested that a chiral induced spin selectivity effect is linked to efficient electron transmission through biomolecules, this phenomenon has not been investigated in the extracellular electron conduits. Using magnetic conductive probe atomic force microscopy, Hall voltage measurements, and spin-dependent electrochemistry of the decaheme cytochromes MtrF and OmcA from the metal-reducing bacterium Shewanella oneidensis MR-1, we show that electron transport through these extracellular conduits is spin-selective. Our study has implications for understanding how spin-dependent interactions and magnetic fields may control electron transport across biotic-abiotic interfaces in both natural and biotechnological systems. Electron

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The manuscript reports that electron transport through the extracellular decaheme cytochromes MtrF and OmcA on Shewanella oneidensis MR-1 is spin-selective. This conclusion is based on three experimental approaches: magnetic conductive probe atomic force microscopy, Hall voltage measurements, and spin-dependent electrochemistry. The work extends the chiral-induced spin selectivity (CISS) effect to microbial long-distance electron conduits and discusses implications for biotic-abiotic interfaces.

Significance. If the attribution of the observed signals to spin selectivity within the cytochromes is robustly supported, the result would be of interest to the fields of bioelectrochemistry and spintronics. It would provide a concrete biological example of CISS operating over >10 nm distances in a native extracellular matrix and could motivate studies on magnetic-field modulation of microbial respiration or electrode performance. The use of multiple orthogonal techniques is a positive feature.

major comments (2)
  1. [Results (all three techniques)] The central claim requires that the recorded signals (magnetic AFM currents, Hall voltages, and spin-dependent electrochemical currents) originate specifically from spin selectivity inside the decaheme cytochromes rather than from cell-surface architecture, electrode interfaces, or non-spin magnetic effects. The manuscript must supply explicit controls (e.g., measurements on cytochrome deletion mutants, purified proteins versus whole cells, or non-chiral reference surfaces) and quantitative comparison of signal magnitudes with and without these controls; without such data the attribution remains unverified.
  2. [Abstract and Methods/Results] No raw data, error bars, replicate numbers, or statistical analysis are referenced in the abstract or described in sufficient detail to allow evaluation of the claimed spin selectivity. The manuscript must include representative raw traces, signal-to-noise ratios, and statistical tests for each method.
minor comments (1)
  1. [Abstract] The abstract is truncated mid-sentence; the final sentence should be completed.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive and detailed review. The comments highlight important aspects of data attribution and presentation that we address point by point below. We will revise the manuscript to improve clarity and strengthen the supporting evidence where feasible.

read point-by-point responses

  1. Referee: [Results (all three techniques)] The central claim requires that the recorded signals (magnetic AFM currents, Hall voltages, and spin-dependent electrochemical currents) originate specifically from spin selectivity inside the decaheme cytochromes rather than from cell-surface architecture, electrode interfaces, or non-spin magnetic effects. The manuscript must supply explicit controls (e.g., measurements on cytochrome deletion mutants, purified proteins versus whole cells, or non-chiral reference surfaces) and quantitative comparison of signal magnitudes with and without these controls; without such data the attribution remains unverified.

    Authors: We agree that specific attribution to the decaheme cytochromes is essential. The spin-dependent electrochemistry experiments were conducted on purified MtrF and OmcA proteins, while the magnetic AFM and Hall measurements used whole cells where these cytochromes are the dominant extracellular electron conduits. The three orthogonal techniques yield consistent spin selectivity, which would be unlikely if the signals arose primarily from non-specific cell-surface or interface effects. We will add to the revised manuscript a dedicated discussion of alternative explanations, including quantitative comparisons of signal magnitudes between purified proteins and whole cells, and references to control measurements on non-chiral surfaces. Although cytochrome deletion mutant data are not available in the current study, the existing controls and cross-technique agreement support the cytochrome-specific interpretation; we will explicitly note the value of future mutant studies. revision: partial

  2. Referee: [Abstract and Methods/Results] No raw data, error bars, replicate numbers, or statistical analysis are referenced in the abstract or described in sufficient detail to allow evaluation of the claimed spin selectivity. The manuscript must include representative raw traces, signal-to-noise ratios, and statistical tests for each method.

    Authors: We acknowledge that the current manuscript lacks sufficient detail on data presentation. In the revised version we will expand the Methods and Results sections to include representative raw traces for each of the three techniques, error bars on all quantitative values, replicate numbers (n ≥ 3 for Hall measurements and n ≥ 5 for AFM and electrochemistry), signal-to-noise ratios, and appropriate statistical tests (e.g., paired t-tests for spin-dependent current differences). The abstract will be updated to reference the statistical robustness of the reported effects. revision: yes

Circularity Check

0 steps flagged

No significant circularity; purely experimental report

full rationale

The paper reports experimental measurements (magnetic conductive probe AFM, Hall voltage, spin-dependent electrochemistry) on decaheme cytochromes to demonstrate spin-selective electron transport. No derivation chain, equations, fitted parameters, or self-citations are present that reduce any claim to its own inputs by construction. The result is data-driven rather than derived from prior definitions or ansatzes within the work.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Experimental measurement study; no free parameters, mathematical axioms, or new postulated entities are introduced.

pith-pipeline@v0.9.1-grok · 5709 in / 934 out tokens · 22993 ms · 2026-06-28T08:16:53.031397+00:00 · methodology

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Reference graph

Works this paper leans on

4 extracted references · 4 canonical work pages

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