Microbially influenced corrosion is of great industrial concern. Microbial coupling of metal oxidation to sulfate-, nitrate-, nitrite-, or CO2-reduction is proton-mediated, and some sulfate-reducing prokaryotes are capable of regulating extracellular pH. The analysis of the corrosive processes catalyzed by nitrate reducing bacteria and methanogenic archaea indicates that these microorganisms may be capable of regulating extracellular pH as well. It is proposed that nutrient limitation at metal-biofilm interfaces may induce activation of enzymatic proton-producing/proton-secreting functions in respiratory and methanogenic microorganisms to make them capable of using Fe0 as the electron donor. This can be further verified through experiments involving measurements of ion and gas concentrations at metal-biofilm interfaces, microscopy, and transcriptomics analyses.