Enzyme confirmed to extract electrons, causing iron corrosion

February 17, 2018

Hints for developing enzyme-targeted anticorrosion chemicals with a low environmental impact

A joint NIMS– RIKEN CSRS research team has clarified that bacteria that accelerate iron corrosion in oil-well drilling pipelines have outer-membrane cytochromes that directly extract electrons from iron. It is important to clarify the cause of such corrosion and prevent it, since such corrosion could result in a major oil spill should a pipeline rupture.

Sulfate-reducing bacteria that extract electrons from iron by taking advantage of iron sulfide’s electrical conductivity have been reported, and such electron extraction has been noted as a cause of iron corrosion. However, the enzymes extracting the electrons were not yet identified and the detailed mechanism remained unknown.

The team analyzed the cell membranes of sulfate-reducing bacteria that grow using iron as an electron source, discovering a group of enzymes that differ greatly in amino acid sequence from previously reported electron-extracting membrane enzymes.

Researchers confirmed that electrons are extracted from the electrode only when the enzyme is highly expressed. The results provide direct evidence that corrosion-accelerating bacteria are drawing electrons straight from iron. Furthermore, when the research team queried the newly discovered enzyme group on a bacterial protein database, it revealed that these enzymes are also widely found in bacteria living in deep sea sediments.

Currently, corrosion countermeasures are carried out with exhaustive sterilization using antibiotics. However, these findings are expected to contribute to advancement of a corrosion prevention method that is efficient and has less environmental impact, such as the development of drugs targeting the discovered enzymes.

Original article
Science Advances doi:10.1126/sciadv.aao5682
X. Deng, N. Dohmae, K. H. Nealson, K. Hashimoto, A. Okamoto,
"Multi-heme cytochromes provide a pathway for survival in energy-limited environments".
Naoshi Dohmae
Unit Leader
Biomolecular Characterization Unit