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Making a meal of iron.

Making a meal of iron

While Popeye can count on spinach for his source of energy, researchers now report that certain methane-producing microorganisms are able to extract their supply directly from iron in its elemental form. "To our knowledge this is the first demonstration of [metallic iron] as an energy source for growth of any organism and thus represents a novel type of chemolithotrophic energy metabolism,' microbiologist Lacy Daniels and his colleagues at the University of Iowa in Iowa City report in the July 31 SCIENCE.

Methane-generating bacteria, which thrive in an oxygen-free environment, normally produce methane and water by combining hydrogen gas and carbon dioxide. Working with pure cultures of various methane-generating bacteria, Daniels and his group showed that these organisms can also grow and produce methane in the presence of iron. In this case, iron reacts with hydrogen ions to produce iron ions and hydrogen gas. Although thermodynamic calculations show that this reaction is energetically unfavorable, the continual removal of hydrogen by the bacteria keeps the iron reaction going. One result is that the iron is oxidized.

"Our work suggests that methanogens could contribute significantly to metal corrosion in anaerobic areas,' the researchers conclude. These organisms can be found in sediment at the bottom of almost any lake, pond or stream from the Arctic to the equator, says Daniels. Metal objects buried in soil or sediment, submerged in water or inside containers such as anaerobic digestors would be vulnerable. "In these systems,' he says, "[hydrogen gas] is often present in only low levels and [carbon dioxide] is abundant, so that [elemental iron] could serve as a significant electron donor.'

The finding is important because researchers interested in biocorrosion have in the past concentrated their efforts almost exclusively on sulfate-reducing bacteria (SN: 7/20/85, p.42). Now a second family of bacteria capable of corroding metal has entered the picture.
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Title Annotation:some methane-producing bacteria extract energy from iron
Publication:Science News
Date:Aug 15, 1987
Words:312
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