Microorganisms: Induction and inhibition of corrosion in metals

• Involvement of microorganisms in corrosion makes it more complex and confusing.
• Microbes play role in both corrosion induction and inhibition.
• Various factors affect the inhibitive behaviors of microorganisms.
• Corrosion inhibitor microbe should be selected based on the operating conditions.

Corrosion occurs due to chemical or electrochemical reactions between the environment and metal. It can cause dangerous and expensive damage to a wide range of industries. However, it is difficult to evaluate the economic impact of corrosion, particularly when microorganisms are involved in the corrosion mechanism. Microbes change the electrochemical reaction at the biofilm/metal interface and either inhibit or accelerate the process of metal corrosion. The high cost, toxicity, and sometimes ineffectiveness of present physical and chemical strategies to control corrosion have called for the use of microorganisms in inhibitory mechanisms, and this has generated great interest. Although the microbial inhibitory mechanism is environmentally friendly, the predictability of the results is not yet affirmed, as sometimes the same bacteria with an inhibitory property may also become aggressive. This review discusses different mechanisms by which microbes induce or inhibit corrosion in metals. Further, as the corrosive or inhibiting behaviors of microorganisms vary considerably depending on environmental factors, the roles of these factors are also emphasized.