New champions among corrosive microbes

In another example of the deep sea’s largely unexplored biodiversity, scientists have discovered two new strains of bacteria that corrode iron with unprecedented efficiency.

In marine environments that are oxygen poor, certain bacteria are known to eat away at iron by converting sulfate in ocean water into the corrosive chemical hydrogen sulfide. To search for other microorganisms adept at causing corrosion, Friedrich Widdel at the Max Planck Institute for Marine Microbiology in Bremen, Germany, and his colleagues collected sediments from the North Sea and isolated several strains of bacteria from the material. The researchers then cultured the bacterial strains separately inside sealed glass tubes containing iron granules.

After several weeks, the researchers compared how much iron was consumed by each strain. In the Feb. 26 Nature, the researchers describe two new strains that corrode iron at a much faster rate than any previously known microbial corroder.

Widdel says the unusually high corrosion rate suggests that the bacteria consume iron using a different mechanism that other microbes do. The researchers hypothesize that when these strains form a film on the iron, they extract electrons directly from the iron surface, thereby revving up the rate of hydrogen sulfide production. Although it is unclear how the bacteria do this, Widdel says that proteins on the cells’ surfaces might act as electrical connections across which electrons flow from the iron to the cells.

It’s possible that these bacteria are the primary culprits of iron corrosion in wet settings and affect structures as varied as sewage tanks and oil rigs, adds Widdel.

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