Viruses of Viruses
One of the cool things about biology is that even parasites can have parasites, and those parasites can have parasites…
P2 is a virus that attacks E. coli bacteria (a “bacteriophage”, from the Greek word phagos which means “one who eats”). P2 sometimes lies dormant in E. coli for a while, until for whatever reason it decides to pop out and take over the bacterium to make copies of itself again. When P2 becomes active, its DNA, which was also lying dormant, becomes active and forces the host to make new viruses. The P2 DNA carries the blueprints for the proteins that form its outer coating, which lets it infect other bacteria.
Viruses are really just tiny parasites that taking control of bacteria and force them make new viruses.
P4 is another bacteriophage, but it’s kind of crappy; it doesn’t have genes for its outer coat, so it can’t even make copies of itself! If there is a P2 lying dormant in the same cell, however, P4 will commandeer the other virus’s genes and use its head and tail proteins for itself to make new P4 viruses (instead of P2 viruses). So P4 is really a parasite of P2, which is itself a parasite of bacteria!
Another parasite of a virus is SaPI1, a “pathogenicity island,” which is a piece of DNA found in Staphylococcus aureus, a bacterium that’s responsible for tons of deadly infections these days in schools, hospitals, and prisons. Staph is one of the leading killers of people in the US. But that’s a whole different topic unto itself…
Anyway, pathogenicity islands are pieces of DNA that can cut themselves out of bacterial DNA and reinsert in other parts. One pathogenicity island related to SaPI1 encodes for the protein that causes toxic shock syndrome in humans when they get a staph infection. Normally, pieces of DNA aren’t infectious or anything.
SaPI1 is an interesting island, in that it can actually get out of bacteria and infect other ones! It’s like a virus, but again, it can’t make the virus coat proteins it needs to actually infect other bacteria. But what it can do is take control of a dormant 80-alpha virus! SaPI1 forces 80-alpha to make coat proteins for the SaPI1, which then leaves the current host and goes to infect other cells. So, SaPI1 is a parasite of 80-alpha, which is a parasite of S. aureus, which can infect humans.
In the end, I guess we’re just at the bottom of a whole ‘nother food chain. But it’s a really awesome food chain!
