The Corrosion Effects of Sulfate- and Ferric-Reducing Bacterial Consortia on Steel

Fourteen thermotolerant and thermophilic bacterial isolates from a hot spring in Guanajuato State, Mexico, were tested for their ability to induce the corrosion of carbon steel in monocultures and, in selected cases, in mixed cultures and co-culture with a sulfate-reducing strain, SRB-M. Characterization by 16S rDNA showed that three of the thermophilic isolates (G9a, G9c, and G11) belong to the genus Bacillus , one (G2) showed homology with Bacillus as well as Geobacillus , and the SRB-M strain is closely related to Desulfotomaculum sp. Ten of the fourteen thermophilic and thermotolerant isolates promoted significantly more corrosion than the sterile controls. Under microaerobic batch-culture conditions at 55°C, SRB-M in monoculture did not show a corrosive effect measured as weight loss; in a mixed culture with G2, G9a, and G11, however, the final corrosion was enhanced 3.6 times when compared to sterile controls. Co-cultures of "G" isolates with SRB-M showed various effects on the final corrosion, ranging from 1.4 to m 1.2 times the control rates. Interestingly, G2, the only isolate able to reduce ferric ion, had the largest effect on microbial induced corrosion in mixed culture. Two different models of thermophilic bacterial communities, reconstructed with ferric- and sulfate-reducing isolates, had corrosion rates 4.8 and 5.0 times higher than the sterile controls. Our data show that bacterial strains with hydrogenase activity are not necessarily corrosive and that corrosion induction can be modified substantially by the metabolic background provided by the larger bacterial community, especially its ferric-reducing members.