For the first time, biologists have directly shown how spontaneous mutation of a small RNA (sRNA) regulatory molecule can provide an evolutionary advantage. Reporting in this week's Science, Indiana University Bloomington scientists also identify the sRNA as a key regulator of social behavior in Myxococcus xanthus, a soil bacterium widely studied for its ability to cooperatively construct fruiting bodies that house stress-resistant spores when food runs out.
"We'd been asking how one of our experimental lineages had re-evolved the ability to make fruiting bodies and ended up discovering a completely new aspect of Myxococcus biology," said IU Bloomington evolutionary biologist Gregory Velicer.
A genetic change in the sRNA of interest, 'Pxr', had been previously found to give an evolved mutant of M. xanthus a competitive edge over both the mutant's immediate parent, a social "cheater" that does not make fruiting bodies, and that cheater's own ancestor, a cooperative wild-type strain that does construct fruiting bodies. IU Bloomington molecular biologist Yuen-Tsu Nicco Yu and Velicer had been investigating how the mutation converted the socially inept parental cheater into a new strain with a restored capacity to make fruiting bodies.