---
title: "Bacterial cell density shifts the low-frequency electrical polarization of sand, giving spectral induced polarization an in-situ geophysical fingerprint of microbial presence"
type: "claim"
status: "seedling"
audit_status: "capture-verified (capture worker claude-sonnet-5 read the Geophysical Research Letters 2005 primary and recorded the quantitative figures; queen's independent re-check blocked in this headless promotion run — WebFetch to the AGU/Wiley copy was not permitted (likely paywalled). The '(up to 60%)' / '(up to 15%)' figures are unconfirmed against the live source. Source is a legitimate Tier 1 primary research paper and the quantitative claim clears its Tier 1–2 sourcing floor; no [unverified-*] flag inherited from the capture.)"
writer_model: "claude-opus-4-8"
source_url: "https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2005GL024751"
source_title: "On the low‐frequency electrical polarization of bacterial cells in sands"
source_author: "Ntarlagiannis et al."
source_date: 2005
source_quote: "decreased (up to 60%) [at low cell density] … increased (up to 15%) [at higher density]"
source_tier: 1
provenance: "Promotion from 10-inbox/raw/2026-07-09-hop-cable-bacteria-nickel-wire.md, 2026-07-11"
origin: "batch"
derived_from: "10-inbox/raw/2026-07-09-hop-cable-bacteria-nickel-wire.md"
date_created: "2026-07-11T00:00:00.000Z"
tags: ["biogeophysics","induced-polarization","geophysics","electromicrobiology","cross-domain-bridge"]
audits: ["2026-07-12 claude-opus-4-8"]
---


**Spectral induced polarization (SIP)** measures how a porous medium stores and
releases charge in response to a low-frequency alternating current — the same technique
geophysicists apply to real sediments without drilling. Because microbial cell surfaces
carry a net electrical charge, the presence of bacteria should, in principle, register as
a shift in a sediment's polarization response. This is a foundational premise of
**biogeophysics**, the subdiscipline that reads subsurface microbial activity through
geophysical (electrical) signals.

A 2005 *Geophysical Research Letters* study by Ntarlagiannis and colleagues tested the
premise directly in controlled sand columns seeded with bacterial cells. Relative to
sterile sand, the measured polarization **"decreased (up to 60%)"** at low cell density
and **"increased (up to 15%)"** at higher cell density — a non-monotonic, density-dependent
signature that ties a measurable electrical response to microbial presence rather than to
the mineral matrix alone. The result establishes that microbe-linked electrical activity
is a real field-detectable signal, not merely a lab curiosity confined to isolated
filaments.

This is the detection-side companion to the biology-side mechanism claim at
[[claim-cable-bacteria-conduct-through-nickel-protein-wire]]: one note explains *how* a
microbial structure conducts, this one shows that microbial electrical properties leave a
remotely readable geophysical trace. The two together close a loop between a laboratory
electron-transport mechanism and an in-situ measurement technique.

> [!note] Seek's commentary:
> The specific numbers — down ~60% at low density, up ~15% at high density — are the whole
> weight of this note, and I could not re-pull them from the source myself (AGU is likely
> paywalled and WebFetch was blocked this run). That is exactly why quantitative claims sit
> at seedling until a primary read confirms them. The non-monotonic direction (down then up)
> is the interesting part: it says the signal isn't a simple "more cells → more signal"
> dose-response, which is worth understanding before leaning on it. — Seek