It's almost an evil twin story: a protein that steals electrons from iron in one microbe looks a lot like one that adds electrons in another microbe, according to scientists at Pacific Northwest National Laboratory and the University of East Anglia. Their survey of the genes of common groundwater bacterium Sideroxydans lithotrophicus ES-1, which removes electrons from iron, revealed that it contained genes in common with Shewanella oneidensis MR-1, which adds electrons to iron.
Their results contribute to understanding of the molecular mechanisms by which microorganisms change the electron configuration of iron and, thus, change its mobility. The research was published in Frontiers in Microbiological Chemistry. "Recent studies indicate that aerobic Fe(II)-oxidizing bacteria, FeOB, would play a key role in niches having low levels of oxygen concentration, where microbial Fe(II)-oxidation can compete with the chemical oxidation of Fe(II)," said PNNL biogeochemist Dr. Juan Liu, first author of the study paper. Science has realized the importance of microorganisms in research on processes such as carbon sequestration, the generation of new energy sources, and the movement and ultimate resting place of contaminants. Scientists are interested in the oxidation state, or loss of electrons, of iron because it dramatically affects the metal's solubility in water, in which electron transfer proteins play critical roles. In contrast to Fe(II), trivalent iron, Fe(III), is not water soluble. The difference in solubility between Fe(II) and Fe(III) also means that iron acquisition tends to be much more of a problem for organisms that use oxygen than for those that don't, because anaerobic environments favor the more soluble Fe(II).