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

Area of Science:

• Microbiology
• Materials Science
• Electrochemistry

Background:

• Electroactive microbes can corrode stainless steel, a phenomenon previously attributed to physical breaching of protective passive films.
• This microbial corrosion allows direct electron transfer from the metal (Fe0) to microbes for anaerobic respiration.

Purpose of the Study:

• To investigate the mechanism by which the electroactive microbe Geobacter sulfurreducens corrodes stainless steel.
• To challenge the prevailing assumption that direct microbial contact with Fe0 is necessary for corrosion.

Main Methods:

• Utilized Geobacter sulfurreducens and stainless steel samples.
• Investigated microbial interaction with the passive chromium oxide film.
• Assessed electron transfer mechanisms and film integrity.

Main Results:

• Geobacter sulfurreducens, despite high corrosive activity, does not physically breach the stainless steel's passive film.
• Biologically mediated electron transfer occurs across an intact chromium oxide layer.
• The intact film remains insulating to abiotic proton reduction.

Conclusions:

• Electroactive microbial corrosion of stainless steel does not require physical breaching of the passive film.
• Electron transfer can occur across intact, insulating oxide layers.
• Findings offer new strategies for designing corrosion-resistant metals.