Bacteria plus four other environmental conditions must be present for MIC

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For microbiologically influenced corrosion/MIC and growth of microbes, the bacteria plus four other environmental conditions must be present:

Metals (host location)
Nutrients
Water, and
Oxygen (although certain types of bacteria need only very small amounts of oxygen)

Microbial growth depends on the presence of all of these environmental conditions. When the nutrients in the system are consumed, the microbes may become dormant. When the environmental condition, i.e. nutrients, is replenished, the microbial growth resumes.

For examples of this replenishment include: draining and refilling of systems, addition of water to replenish losses from leaks or maintenance, or the periodic filling of dry fire sprinkler systems.

The predominant types of bacteria found in association with MIC related corrosion:

Sulfate-Reducing Bacteria (SRB)
Bacteria that converts sulfate ions to sulfides (including hydrogen sulfide). These bacteria can grow in low oxygen environments. SRB require sufficient organic nutrients.

Iron-Related Bacteria (IRB)
Bacteria that converts soluble iron ions (ferrous) to insoluble iron ions (ferric). The ferric iron is deposited on the piping or system surfaces, creating deposits that are host sites where other bacteria can grow. These can be present in a wide variety of environmental conditions as they may be aerobic or anaerobic.
Low Nutrient Bacteria (LNB)
Bacteria that grow in environments, such as potable water, with very low concentrations of nutrients. LNB growth will form slimes and deposits which creates host sites where other MIC bacteria can grow.
Anaerobic Bacteria
bacteria that grow in the absence of abundant free oxygen. These bacteria can grow in environments with as little as 50 parts per billion (ppb) dissolved oxygen.
Aerobic Bacteria
bacteria that grow in the presence of free oxygen.