““When Hamiltonella's genome was sequenced, the real reason behind the bacterium's protective powers became apparent: about half of its DNA actually belonged to a virus. It was a phage - one of those spindly-legged, mucus-loving viruses that we met before. They typically kill bacteria by reproducing inside them and bursting fatally outward. But they can also opt for a more passive lifestyle, where they integrate their DNA into a bacterium's genome and stay there for many generations. Dozens of these phages now hide within Hamiltonella. The viruses are Hamiltonella's fists; they give the bacterial bodyguard its punch. Oliver showed that when Hamiltonella carries a particular phage strain, it renders aphids almost totally wasp-proof. If the virus disappeared, the same bacterium became useless, and almost all of its aphid hosts succumbed to their parasites. Without the phage, Hamiltonella might as well have been completely absent for all the good it did. The phages could be poisoning the wasps directly: they certainly mass-produce toxins that can attack animal cells, but don't seem to harm the aphids. Alternatively, they could split Hamiltonella apart, causing the bacteria's own toxins to spill onto the wasps. Or maybe the viral and bacterial chemicals are working together. Whatever the case, it is clear that an insect, a bacterium, and a virus have formed an evolutionary alliance against a parasitic wasp that threatens them all.””
