Insights into origin and evolution of strange virus-like elements

Some microorganisms produce nanostructures that morphologically and genetically resemble viruses, but don’t behave like typical viruses. Oddly, these structures package random pieces of DNA of their microbial host and, as a result, do not appear to propagate by infecting microbes and making more copies of themselves. Since these elements can deliver the packaged DNA to other cells, they were dubbed gene transfer agents (GTAs). It is not clear whether GTAs represent atypical viruses, defective viruses, or viruses co-opted by the microorganisms for some function. In a new study, Prof. Zhaxybayeva’s group used evolutionary analyses of GTA-like genes to show that a GTA in alpha-proteobacteria likely co-evolved with its bacterial host for at least 700 million years, suggesting that this GTA is unlikely to be a defective virus. The function of this GTA remains to be elucidated in the future work.

Image: Charcoal drawing of an alpha-proteobacterial GTA by Amy Yun Zhang '17.