# Electroactive Microbes Short-Circuit the Passive Film to Corrode Stainless Steel

## TL;DR

Electroactive microbes like Geobacter sulfurreducens corrode stainless steel by transferring electrons through the protective passive film without physically breaking it.

## Contribution

The study reveals that electron transfer can occur across an intact passive film, challenging the assumption that microbes must directly contact metal to cause corrosion.

## Key findings

- Geobacter sulfurreducens does not physically breach the passive film on stainless steel.
- Electron transfer occurs across an intact chromium oxide-rich passive film.
- The passive film remains insulating enough to block abiotic proton reduction.

## Abstract

Electroactive microbes are uniquely capable of aggressively corroding metals like stainless steel that were once thought immune to microbial attack. This activity has been attributed to microbial destruction of the protective chromium oxide passive film on the stainless steel surface that protects the underlying Fe0 from corrosive agents, allowing the microbes to establish direct electrical contact with the Fe0 and extract electrons to support anaerobic respiration. We show here that the electroactive microbe Geobacter sulfurreducens, despite its high corrosive activity, is unable to physically breach the passive film. Instead, it enables biologically mediated electron transfer across an intact chromium oxide-rich layer that remains sufficiently insulating to block abiotic proton reduction. These findings challenge the prevailing assumption that electroactive microbes must directly contact Fe0 for corrosion and provide new guidance for the design of corrosion-resistant metals.