Single-celled extremophiles can deal with toxic uranium in very different ways

At io9, we love extremophiles, the litte creatures which can survive and thrive in the most insane conditions our planet has to offer. A new study has shown that even when two extremophiles are very closely related, they can handle toxic conditions in very different ways.

Metallosphaera sedula and Metallosphaera prunae are two extremely closely related thermoacidophiles. They live in highly acidic environments where the temperatures sit above 70°C/160°F. M. sedula is found in a hot spring near Vesuvius, and M. prunae does its thing in a "smoldering heap" near an abandoned uranium mine in Germany. These two species are genetically 99.99% identical, but handle uranium in very different ways.

When faced with toxic levels of uranium, M. prunae goes dormant until the threat is removed, at which point it fires back up and returns to normal. M. sedula, on the other hand, is actually capable of feeding on the uranium, and is the first known organism that can use the metal as an energy source.

The researchers theorize that M. prunae is an offshoot of M. sedula, with a mutation to handle the toxicity in a different way. One shuts down, the other feeds on the poison. While this study can branch in a lot of ways right now: using M. sedula to help with mining or gathering better understanding how antibiotic resistance can evolve. But lead researcher Dr. Robert Kelly has used it to make an interesting point about genetic analysis and speciation:

"How do we classify microorganisms now that we can compare genomes so easily? These are not different species by the classical definition because their genomes are virtually identical, but they have very different phenotypes, or lifestyles, when faced with stress."

In the article, he concludes:

A larger issue that arises is how to bridge microbial taxonomy between the pregenomics and postgenomics eras. What constitutes a new genus, species, or strain of a microorganism now compared with then? The close relationship between the genomes of M. sedula and M. prunae suggests that one is likely the progenitor of the other; however, their vastly different growth physiology in the presence of [uranium], in the absence of genome sequence information, would have made this determination difficult. Going forward, one wonders how much of our previous understanding of microbial biology, extremophily, or otherwise is based on confusion between genotype and phenotype.

Photo by Danilo Russo.