Microbiology Editor's Choice: anti-parasitic protection from phage

Posted on September 2, 2019   by Microbiology Society

Each month, a manuscript published in our flagship journal Microbiology is chosen by a member of the Editorial Board. This month, the paper is titled 'Bacteriophage acquisition restores protective mutualism.' It was chosen by Dr Jen Cavet.

The bacterial symbiont Hamiltonella defensa protects the pea aphid Acyrthosiphon pisum against the parasitic wasp Aphidius ervi. However, this protection only occurs when the bacteria are infected with a bacteriophage (A. pisum secondary endosymbiont, APSE).
Natural knock-out experiments have suggested that APSE carries the genes responsible for this symbiotic phenotype and a history of horizontal movement has been suggested from phylogenetic studies. Nonetheless, lateral transfer of APSE in vivo has never previously been shown. Here, the authors show that APSEs can indeed move laterally into recipient phage-free, non-protective H. defensa within aphids, and fully restore anti-parasite protection. However, phage transfer only occurred when APSE and donor H. defensa were simultaneously injected into the aphids, and not when phage particles were injected alone. Hence, while demonstrating that phage can move horizontally among heritable bacterial symbionts within a host, this study suggests that natural barriers may also exist.

Bacteriophage acquisition restores protective mutualism 

Most animals, including insects harbor bacterial symbionts that play key roles in nutrition and defense. Aphids are herbivorous insects with numerous symbionts, including some that defend against natural enemies. One called Hamiltonella protects against internally developing parasitic wasps that could kill the aphid. Complicating matters Hamiltonella is only protective when it carries APSE viruses. Here we show APSEs can jump from an infected bacterial strain to a virus-free strain within aphids, rapidly creating a host that is resistant to parasitism. This study confirms experimentally that viruses can transfer ecologically important traits among symbionts that persist to defend future generations of aphids.

Nicole Lynn-Bell: I’m a doctoral candidate in the Department of Microbiology at the University of Georgia, currently in my fifth year and nearing the finish line of my PhD marathon.

Over time, I have developed a deep appreciation for the diversity, pervasiveness, and functionality of microbes in mediating species interactions. I am captivated by my current research project because it highlights just how important symbionts can be for hosts in their routine ecological interactions. My research focuses on the diversity and function of the bacterial symbiont, Hamiltonella defensa, which resides inside and protects plant-feeding aphids against attack by parasitic wasps.

The most rewarding parts of my work include the excitement of novel discoveries and sharing with others how sophisticated life can be! If I weren’t a scientist… I’d be a nature show host exploring, researching, and sharing stories with others about the amazing diversity of life on our little blue planet.

To access the full paper, click here. Editor's Choice articles published in Microbiology are free to read.