Enlarge / Viruses latch on to a cell, setting off a competition for a successful infection. (credit: Graham Beards/Wikimedia Commons)

Darwin’s theory of evolution was formulated based on the competition he saw among animals and plants. But his insights turned out to apply with organisms he couldn’t see. At the microbial level, organisms compete fiercely with each other for resources, and often devote a fair bit of energy to trying to kill off the competition (and, in some cases, eat it).

So it shouldn’t come as a surprise that this sort of competition extends to the smallest biological realms possible: the viruses. A new paper takes a look at viruses that infect just a single species of bacteria, and finds that many of them carry genes that allow them to block the competition from infecting their hosts.

Many of the viruses that infect bacteria are brutal killers, exploding their hosts shortly after infection in order to spread their progeny to new victims. But others are quite a bit more devious in their infections. They’ll integrate themselves into their host’s genome, lying low for many generations before undergoing the normal explosive infection cycle. This lets them infect more hosts each time their current one divides, and allows their victims to grow and spread, rather than wiping them out at once.