Iron-Eating Bacteria Clean Up Contaminated Environments - By Cathy Holding

[iansmith]

Novel bacteria could clean up heavy metal- and chlorine-contaminated environments | By Cathy Holding

Microorganisms can corrode metallic iron in an indirect process caused by chemicals released by sulfate-reducing bacteria. In a paper in the February 26 Nature, researchers have identified marine bacteria that directly attack the metal (Nature, 427:829-832, February 26, 2004).

Hang Dinh and colleagues at the Max Planck Institute for Marine Microbiology, Bremen, recovered organisms from marine sediment that could pave the way to a greater understanding of corrosive processes in the natural environment. Such information could be extremely valuable to many companies, including those in the petroleum industry.

Marine sediment was collected near Wilhelmshaven, in the North Sea, and bacteria isolated from the samples were cultured with iron granules for 7 weeks. The reduction in the mass of iron was assessed by gravimetry, and bacteria from cultures in which the mass of iron decreased were assigned a phylogeny on the basis of 16S rRNA gene sequences.

“When we talk about metal corrosion, we're talking about several percentages of the gross national product, so this is not a small problem,” said Judy D. Wall, a professor of biochemistry at the University of Missouri-Columbia, who was not involved in the study.

“There are other microbes out there that put electrons onto Fe3 and generate Fe2, and those are often referred to as breathing iron. In this case, it's more like eating iron,” Wall told The Scientist. She explained that the newly identified organisms pull electrons from metallic iron and then deliver them to sulfate compounds. “So they're breathing sulfate or they're breathing protons, and producing hydrogen,” she said.

The idea now is that these organisms obtain electrons directly from metallic iron in the form of Fe0 (iron zero). “That's the hypothesis to explain how these organisms grow relatively rapidly compared to classical well known species,” Friedrich Widdel, coauthor of the paper, told The Scientist. “The hypothesis concerning hydrogen scavenging was not fully consistent, and so our idea was that there might be something [else] behind anaerobic corrosion.”

Widdel, professor and managing director of the Max Planck Institute for Marine Microbiology, said that the sulfate-reducing bacteria commonly tested in corrosion laboratories were from culture collections that had been isolated with organics, and may not necessarily be the corroding species in situ. “The idea was to start from scratch, to start with sediment with iron in it to see what would develop,” Widdel said.

Derek Lovley, professor and head of the Department of Microbiology, University of Massachusetts, told The Scientist, “Corrosion has been studied a lot with different microorganisms, but not necessarily ones that were specifically recovered from a corroding surface.”

Widdel said he does not think these bacteria have a role in bioremedial applications. But Lovley, who was not involved in the study, said he believes these organisms may explain the clean-up of chlorinated solvents. “You can add metallic iron to the contaminating environment as a source of electrons,” he said. “It's apparent now from this study... that microorganisms could be degrading some contaminants [by] getting electrons from some of that iron metal.” He also said that it might now be possible to use iron as the electron source to promote uranium reduction in contaminated ground water.

Widdel said that he thinks that metallic iron is a very recent substrate for bacteria on the evolutionary scale. Since it has been introduced by humans, he said he believes that time is too short for bacteria to have evolved a metabolic system to use it, and so suggests that they must have got electrons from somewhere else before iron was introduced into the environment. “It's a little bit of a wide speculation,” he said, “but why not attach to other bacteria which had problems getting rid of electrons because they use organics?”

Widdel said that the paper should not be regarded as providing the complete answer to the corrosion story. “The whole group of sulfur-producing bacteria is extremely diverse, and if in the future we look at other places, other species may be found that act in a similar manner,” he said.

“The message is the classical Desulfovibrios, which we get from culture collections, are certainly not the answer to corrosion,” Widdel said.

http://www.biomedcentral.com/news/20040226/01

 

[Phobos]

Good article. I wonder about it's use in conjunction with another new remediation technology for chlorinated solvents...the addition of "nano-scale" (ultrafine) particles of iron.