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Microbial corrosion, also called microbiologically influenced corrosion, is metal degradation caused by microbial metabolic activities. It occurs when microorganisms like bacteria colonize metal surfaces, forming biofilms that alter the local electrochemical environment and produce corrosive substances such as hydrogen sulfide and organic acids, accelerating the corrosion process.

Iron, steel, copper, and aluminum are most commonly affected by microbial corrosion. Carbon steel and stainless steel are also highly susceptible. The extent of corrosion depends on factors including the type of microorganism present, environmental conditions, nutrient availability, and whether anaerobic conditions favor sulfate-reducing bacteria growth.

Sulfate-reducing bacteria accelerate iron corrosion through two mechanisms. First, they consume molecular hydrogen generated during electrochemical pitting, sustaining electron release from the metal. Second, bacteria like Desulfopila corrodens embedded in sulfidic layers directly extract electrons from iron via redox-active proteins to reduce sulfate to sulfide, which reacts with iron to form iron sulfide, promoting localized corrosion.

Biofilm formation is central to microbial corrosion. Microorganisms adhere to metal surfaces and create biofilms that trap corrosive agents and facilitate localized corrosion. These biofilms alter the electrochemical environment around the metal, enabling microbes to produce hydrogen sulfide and organic acids while some species directly extract electrons from the metal surface.

Mitigation strategies include chemical treatments such as biocides and corrosion inhibitors to control microbial growth. Nitrate injection promotes nitrate-reducing bacteria that outcompete sulfate-reducing bacteria, reducing hydrogen sulfide production. Material selection, protective coatings, regular inspection, and cleaning protocols also prevent microbial colonization. Emerging nanomaterial technologies are being explored to enhance corrosion resistance.

Microbial corrosion predominantly affects buried or submerged metal structures in industries including oil and gas, maritime, and water treatment sectors. These environments provide anaerobic conditions that favor sulfate-reducing bacteria and other corrosive microorganisms. Regular monitoring and maintenance in these settings are essential for early detection and prevention.

Yes, certain microbes can directly extract electrons from metals, accelerating corrosion. Bacteria like Desulfopila corrodens use redox-active proteins embedded within electroconductive sulfidic corrosion layers to accept electrons directly from elemental iron. This direct electron transfer mechanism is distinct from hydrogen consumption and represents a significant pathway for microbially influenced metal degradation.