Effect of ferrous ion availability on growth of a corroding sulfate-reducing bacterium

Environmental conditions controlling growth and metabolic activity of the sulfate-reducing bacterium (SRB), Desulfovibrio gabonensis DSM 10636 which had been previously isolated from a corroded oil pipe, was investigated in a homogenous culture. The culture was conducted continuously in order to get steady-state conditions for growth. Several factors, such as stirring conditions, and the flow rate of N2 injection into headspace of the culture, were found to influence growth performances. The maximum growth rate was markedly influenced by Fe2+ concentration in the medium. Surprisingly, removal of Fe2+ and replacement by a mild steel coupon allowed the strain to grow at pH 6.0 but not at pH 7.4. A proposed biocorrosion mechanism by which the excretion of acidic products can promote Fe2+ availability for SRBs is put forward. Lowering the pH, metabolic products, such as acetic acid, increases the level of corrosive sulfides (H2S, HS−). The latter, in turn, promote the attack of metallic iron which produces Fe2+. In such a way, acidic conditions ensure Fe2+ for SBR growth and can account for the persistency of corrosion.