Microbial corrosion, also called bacterial corrosion, bio-corrosion, microbiologically influenced corrosion, or microbially induced corrosion (MIC), is corrosion caused or promoted by microorganisms, usually chemoautotrophs. It can apply to both metals and non-metallic materials.
Some sulfate-reducing bacteria produce hydrogen sulfide, which can cause sulfide stress cracking. Acidithiobacillus bacteria produce sulfuric acid; Acidothiobacillus thiooxidans frequently damages sewer pipes. Ferrobacillus ferrooxidans directly oxidizes iron to iron oxides and iron hydroxides; the rusticles forming on RMS Titanic wreck are caused by bacterial activity. Other bacteria produce various acids, both organic and mineral, or ammonia.
In presence of oxygen, aerobic bacteria like Acidithiobacillus thiooxidans, Thiobacillus thioparus, and Thiobacillus concretivorus, all three widely present in the environment, are the common corrosion-causing factors resulting in biogenic sulfide corrosion.
Without presence of oxygen, anaerobic bacteria, especially Desulfovibrio and Desulfotomaculum, are common. Desulfovibrio salixigens requires at least 2.5% concentration of sodium chloride, but D. vulgaris and D. desulfuricans can grow in both fresh and salt water. D. africanus is another common corrosion-causing microorganism. The Desulfotomaculum genus comprises sulfate-reducing spore-forming bacteria; Dtm. orientis and Dtm. nigrificans are involved in corrosion processes. Sulfate-reducers require reducing environment; an electrode potential lower than -100 mV is required for them to thrive. However, even a small amount of produced hydrogen sulfide can achieve this shift, so the growth, once started, tends to accelerate.
Layers of anaerobic bacteria can exist in the inner parts of the corrosion deposits, while the outer parts are inhabited by aerobic bacteria.
Some bacteria are able to utilize hydrogen formed during cathodic corrosion processes.
Bacterial corrosion may appear in form of pitting corrosion, for example in pipelines of the oil and gas industry. Anaerobic corrosion is evident as layers of metal sulfides and hydrogen sulfide smell. On cast iron, a graphitic corrosion selective leaching may be the result, with iron being consumed by the bacteria, leaving graphite matrix with low mechanical strength in place.
Hydrocarbon utilizing microorganisms, mostly Cladosporium resinae and Pseudomonas aeruginosa, colloquially known as "HUM bugs", are commonly present in jet fuel. They live in the water-fuel interface of the water droplets, form dark black/brown/green, gel-like mats, and cause microbial corrosion to plastic and rubber parts of the aircraft fuel system by consuming them, and to the metal parts by the means of their acidic metabolic products. They are also incorrectly called algae due to their appearance. FSII, which is added to the fuel, acts as a growth retardant for them. There are about 250 kinds of bacteria that can live in jet fuel, but fewer than a dozen are meaningfully harmful. 
In response to increased awareness of the nature and danger of microbial corrosion, a two-day international symposium was held in Perth, Western Australia in February 2007. The symposium, originally proposed by Dr. Reza Javaherdashti, was sponsored by EXTRIN Consultants and Curtin University of Technology, as well as other local industries. It attracted speakers and attendees from as far as Argentina, Brazil, New Zealand, the UK and the United States in addition to Australian representatives. The symposium primarily focussed on the identification of Microbial Corrosion in marine, mining and industrial environments and the best course of action to remove and prevent further attacks.
- Microbiologically Influenced Corrosion (MIC) and Other Forms of Corrosion
- Biogenic sulfide corrosion
- Schwermer, C. U., G. Lavik, R. M. M. Abed, B. Dunsmore, T. G. Ferdelman, P. Stoodley, A. Gieseke, and D. de Beer. 2008. Impact of nitrate on the structure and function of bacterial biofilm communities in pipelines used for injection of seawater into oil fields. Applied and Environmental Microbiology 74:2841-2851. http://aem.asm.org/cgi/content/abstract/74/9/2841
- J. E. Sheridan; Jan Nelson; Y. L. Tan¬. "STUDIES ON THE ‘KEROSENE FUNGUS’ CLADOSPORIUM RESINAE (LINDAU) DE VRIES — PART I. THE PROBLEM OF MICROBIAL CONTAMINATION OF AVIATION FUELS". Tuatara: 29.
- Dialog to odor and biogenic corrosion in sewage, exhaust air arrangements and fermentation gas arrangements
Kobrin, G., "A Practical Manual on Microbiologically Influenced Corrosion", NACE, Houston, Texas, USA, 1993.
Heitz,E., Flemming HC., Sand, W., "Microbially Influenced Corrosion of Materials", Springer, Berlin, Heidelberg, 1996.
Videla, H., "Manual of Biocorrosion", CRC Press, 1996.
Javaherdashti, R., "Microbiologically Influenced Corrosion-An Engineering Insight", Springer, UK, 2008.
D. Weismann, M. Lohse (Hrsg.): "Sulfid-Praxishandbuch der Abwassertechnik; Geruch, Gefahr, Korrosion verhindern und Kosten beherrschen!" 1. Auflage, VULKAN-Verlag, 2007, ISBN 978-3-8027-2845-7.