Bacterial activity at metal surfaces may result in corrosion induction or corrosion inhibition. An important effect of chemoorganotrophic bacteria under aerobic conditions is the removal of oxygen from the metal surface. This is most effectively done by biofilm-forming microorganisms and causes corrosion inhibition. Anaerobes promote corrosion if they consume molecular hydrogen, for example sulfate-reducing bacteria and certain Fe(III)-reducing organisms such as Shewanella putrefaciens. Chemoorganotrophic Fe(III) reducers are of special interest because they remove corrosion products and hence destroy ecological niches for sulfate-reducing bacteria beneath the deposits. Also, these chemoorganotrophic bacteria may cause passivation of the metal surface through the consumption of dissolved oxygen, lowering the open circuit potential and the creation of a protective layer of atomic hydrogen on the metal surface.