Detection of a conserved multi-heme cytochrome gene cluster in severely corrosive sulfate-reducing biofilms

Sulfate-reducing bacteria (SRB), often considered primary culprits of microbially influenced corrosion (MIC), can be highly abundant in engineered anoxic environments such as oil and gas pipelines. The marine lithotrophic SRB Desulfovibrio ferrophilus strain IS5 is increasingly viewed as a model organism for anaerobic steel degradation due to its unrivalled ability to cause severe corrosion in laboratory tests where Fe⁰ provides the only electron donor. Recent studies suggest that multi-heme c-type cytochromes may be involved in the oxidation of Fe⁰ by this strain. We simulated oilfield MIC in bioreactors under sulfate-reducing conditions and observed material degradation rates ranging from negligible (0.01 mm Fe⁰ yr⁻¹) to severe corrosion (2.75 mm Fe⁰ yr⁻¹). DNA shotgun sequencing of severely corrosive mixed microbial communities revealed metagenome-assembled genomes of the Desulfovibrionaceae and Desulfobulbaceae families that contained a similar multi-heme cytochrome gene cluster like strain IS5. This prompted the development of primers and probes for the quantification of a c-type cytochrome in the conserved cluster with a proposed key function in MIC. The so-called micC gene was indeed detectable in all corrosive cultures yet absent in mixed SRB communities that failed to affect steel integrity. We further demonstrated the practical utility of the novel qPCR assay by surveying oil and gas infrastructure across different geographic locations. Here, micC was only detected in those assets with a history of MIC. The systematic quantification of genetic determinants underlying steel corrosion by lithotrophic microorganisms could transform microbial monitoring strategies, allowing for the proactive identification of critical MIC events in industrial applications.