February 14, 2020
Researchers found that the bacteria have an ability to withdraw electrons without any special enzymes. The development of new rust-proof materials is expected
A research group of the NIMS, CSIRO and RIKEN CSRS found that the conductivity of black rust produced by iron corrosion bacteria plays a role in enhancing the activity of the bacteria and accelerating corrosion.
Iron corrosion caused by a type of bacteria called sulfate-reducing bacteria has become a serious problem in infrastructure such as petroleum pipelines. It is known that hydrogen sulfide produced by the metabolism of these bacteria reacts with iron to produce iron sulfide (black rust) that promotes corrosion. It remains unclear, however, as to why the corrosion continues to proceed even after the surface of the iron is covered with iron sulfide, which hinders the development of effective anticorrosion methods. The research group found that sulfate-reducing bacteria with a special enzyme on the surface of plasma membranes could withdraw electrons from iron via iron sulfide and accelerate corrosion. However, sulfate-reducing bacteria without the enzyme sometimes have a high corrosive activity, suggesting that there is a mechanism that promotes corrosion by withdrawing electrons without the membrane enzyme.
In this study, the research group focused on the conductivity of iron sulfide, which is a main component of black rust. A detailed analysis of iron sulfide nanoparticles produced on the surface of the bacteria revealed that these particles have a crystal structure with a high conductivity. Further, a comparison of activities of the bacteria with and without iron sulfide nanoparticles showed that only the bacteria with the particles withdraw electrons from extracellular solid-state electron donors, activating their metabolism. This finding indicates that black rust, which has been considered a useless metabolic byproduct, has a key biochemical function and suggests that sulfate-reducing bacteria can promote iron corrosion by withdrawing electrons without special membrane enzymes.
Further development of iron alloy materials that reduce the conductivity of black rust is expected as a new strategy to prevent corrosion caused by bacteria.
Angewandte Chemie International Edition doi:10.1002/ange.201915196
X. Deng, N. Dohmae, A. H. Kaksonen, A. Okamoto,
"Biogenic Iron Sulfide Nanoparticles to Enable Extracellular Electron Uptake in Sulfate-Reducing Bacteria".
Biomolecular Characterization Unit