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Pomona College Researchers Prove Bacteria Can Extract Iron from Clay in Natural Settings; Finding Could Alter Models of Earth's Carbon Cycle

Pomona College Professor Robert Gaines and John Vorhies, Pomona Class of 2005, have found the first evidence in a natural setting that some microbes can extract iron (Fe) from clay materials. The findings could impact current models of the marine carbon cycle, which is an important control on the CO2 level of the atmosphere. Their work will be published in the March 2009 issue of the journal Nature Geoscience.

Their discovery began with a Pomona College Sedimentology class that went to Utah to collect samples and set up individual research projects. Vorhies continued his work through his final semester at Pomona and after graduation.

“The way the research unfolded was exciting,” says Gaines. “We were examining mineral products in ancient marine sediments and believed that we had found evidence that microbes had actually dissolved minerals in order to access the iron (Fe)…for use in biological processes. While we were conducting this research, a paper was published in Science, documenting that microbes in laboratory settings were capable of doing precisely this—although it was remained unclear if this process could operate in natural settings, for a number of reasons. If it could, it could influence the operation of the carbon cycle. Our paper is the first documentation that this process operates in natural settings and is likely important in the marine carbon cycle.”

The capacity of Fe-reducing bacteria to access a pool of Fe bound in minerals that was previously considered unavailable is important because this process might impact the rates of organic carbon breakdown by bacteria. This process also releases Fe to seawater, where it is available for other biological processes.

Previously, microbial extraction of Fe from clay minerals had been documented only under ideal lab conditions, and only in one type of clay mineral, nontronite. Nontronite is unusually rich in iron and rare globally. It has remained unclear whether this microbial process could occur in natural settings and if common clay minerals, less rich in iron could provide an accessible source.

Vorhies and Gaines found evidence from the marine sedimentary rock record that this process was active in the oceans approximately 505 million years ago, and that it plays a significant role in cycling Fe and other major elements in the oceans.

Their samples were analyzed using Pomona’s Scanning Electron Microscope and Microanalysis facility, and using stable isotope geochemistry of oxygen and sulfur from quartz and pyrite respectively, to reach their conclusions.

Pomona College, one of the nation’s premier liberal arts institutions, offers a comprehensive program in the arts, humanities, social sciences and natural sciences. Its hallmarks include small classes, close relationships between students and faculty, and a range of opportunities for student research.

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