Computer-generated image of anaerobic, spore-forming, Clostridium bacteriaCDC, JAMES ARCHERResearchers at Harvard Medical School used software to run through roughly 60,000 bacterial genomes in search of proteins that, in yeast, would be predicted to behave as prions—that is, become misfolded in a way that passes on the errant structure to like proteins. In doing so, they identified a version of the global regulator Rho encoded in the genome of Clostridium botulinum, the causative agent of botulism. When they injected Cb­-Rho into E. coli to examine the protein’s function, they found that the protein misfolded in a prion-like manner, rendering it nonfunctional and allowing genes normally suppressed by Rho to be expressed.

The study, published last week (January 13) in Science, is the first to identify a prion-like protein in bacteria, suggesting that the emergence of prions predates the evolutionary split between eukaryotes and bacteria,” the...

Bacterial proteins capable of acting like prions could help the microbes to adapt to environmental changes. One of the genes liberated from Rho suppression, for example, allowed E. coli to better adapt to ethanol exposure. Because prions pass on their misfolded shape to like proteins, they may allow bacteria evolve without genomic changes. “Bacteria might need quick responses to their environment, such as dealing with antibiotics,” Peter Chien, a bacterial biochemist at the University of Massachusetts Amherst, who was not involved in the research, told Nature.

For now, the researchers have only studied Cb-Rho in E. coli and yeast. (It could substitute for a known yeast prion, which are not all disease-causing, further pointing to the protein’s prion-like behavior.) But it remains to be seen how Cb-Rho acts in its natural host, C. botulinum, which will prove more challenging to study.

Nevertheless, the discovery of a prion-like protein in bacteria suggests that this molecular behavior is more common than researchers realized, coauthor Ann Hochschild, a bacterial geneticist at Harvard Medical School, told Nature. “Prions are likely to be much more widespread in nature than previously assumed. We believe other prion-forming proteins will be uncovered in bacteria.”

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