Accelerated Microbial Corrosion by Magnetite and Electrically Conductive Pili through Direct Fe⁰‐to‐Microbe Electron Transfer

Abstract

Electrobiocorrosion, the process in which microbes extract electrons from metallic iron (Fe0) through direct Fe0‐microbe electrical connections, is thought to contribute to the costly corrosion of iron‐containing metals that impacts many industries. However, electrobiocorrosion mechanisms are poorly understood. We report here that electrically conductive pili (e‐pili) and the conductive mineral magnetite play an important role in the electron transfer between Fe0 and Geobacter sulfurreducens, the first microbe in which electrobiocorrosion has been rigorously documented. Genetic modification to express poorly conductive pili substantially diminished corrosive pitting and rates of Fe0‐to‐microbe electron flux. Magnetite reduced resistance to electron transfer, increasing corrosion currents and intensifying pitting. Studies with mutants suggested that the magnetite promoted electron transfer in a manner similar to the outer‐surface c‐type cytochrome OmcS. These findings, and the fact that magnetite is a common product of iron corrosion, suggest a potential positive feedback loop of magnetite produced during corrosion further accelerating electrobiocorrosion. The interactions of e‐pili, cytochromes, and magnetite demonstrate mechanistic complexities of electrobiocorrosion, but also provide insights into detecting and possibly mitigating this economically damaging process.

Burning question: Are there sustainable strategies to prevent microbial metal corrosion?

“…Alternatively, microbes can forgo H 2 as an intermediary electron carrier and extract electrons from Fe 0 through outer‐surface electrical contacts. This ‘electrobiocorrosion’ (Xu et al, 2023 ) takes place at the metal‐microbe interface through outer‐surface electrical contacts such as c ‐type cytochromes, conductive minerals, and electrically conductive pili (Hernández‐Santana et al, 2022 ; Holmes et al, 2022 ; Jin et al, 2023 ; Tang et al, 2019 ; Tang et al, 2021 ; Zhou, Li, et al, 2022 ). Cells at distance from the metal surface may also feed on Fe 0 via long‐range electron transfer through conductive biofilms (Jin et al, 2023 ).…”

Review on Microbially Influenced Concrete Corrosion

“…All parameters have a significant impact on the in-depth investigation of microbial concrete corrosion [ 10 ]. In general, bacterial concentrations are obtained by measuring biomass mass [ 121 , 122 ]. Sand and Bock [ 123 ] put concrete cubes into flasks with a mineral salt solution and incubated them on a rotary shaker for 90 min for the detachment of loose material and of adhering microorganisms.…”