"Recent origin of iron oxidation in extant microbial groups and low clade fidelity of iron metabolisms" ASM Journal, Applied and Environmental Microbiology.

Bacteria can oxidize iron to produce energy. As there was plenty of reduced iron available on the early Earth and there is only a little today, it was sometimes thought that bacteria that oxidize iron today are a small remnant of a larger group that used to do it. We studied the evolutionary history of the iron oxidation pathway that modern bacteria use, and we found that they developed that pathway relatively recently: whatever did it in the past is no longer around today. It would probably be hard for any group of organisms to keep doing iron oxidation over billions of years since iron availability is so variable: they are likely to go extinct or lose this ability at some point. We suggest this as a general trend in evolution that traits which are only sporadically useful are commonly lost—and then have to be re-invented or re-distributed—or the trait will go extinct. However, long-term change and turnover have been difficult to observe among microbes owing to their scant fossil record. Studying the evolutionary history recorded in microbial genomes is often the only way to do it: this paper makes use of that approach for a rare documentation of change in the microbial world. 

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