Tuesday, October 11, 2011

Geophaging


Surfing through some back issues of Nature, I came upon this diagram of a virus -- bacteriophage T4 -- injecting its DNA into an E. coli bacterium (click to enlarge). Nothing new here; this is familiar stuff. And yet, I sat there for a minute or two and said, "Wow!"

The Greek phagein means "to eat." In this case, the virus "eats" an E. coli bacterium, a common denizen of the human gut.

When a sensor on a "leg" of the virus comes into contact with an appropriate site on a bacterium, the virus binds to the surface of the bacterial cell, as on the left side of the diagram. A syringe-like mechanism then punctures the cell wall and injects viral DNA.

The viral DNA commandeers the replication machinery of the bacterium and makes a hundred or more copies of the virus -- something it can't do on its own -- causing the bacterium cell to burst open with its teeming load of cloned invaders.

Again, nothing new about this. It's a story we’ve heard before. But what struck me as I looked at the diagram was scale.

An E. coli bacterium is sausage shaped. One hundred could line up end-to-end across the period at the end of this sentence.

And along comes T4, like a spacecraft visiting an asteroid. Ten times smaller than the bacterium. An exquisite little machine. With specialized proteins adapted to penetrating the cell wall. The injector is lowered. Then -- squirt -- the deadly alien DNA.

Dog-eat-dog, on a scale so small that it boggles the imagination that such refined machinery could exist at all. There it is, in the diagram above, the name of the game.

It's all about nucleic acids making copies of themselves. In a sense, that's all we are -- you and I -- big macroscopic machines that allow a particular brand of DNA a better chance to copy itself.

And -- oh, my goodness -- we are doing a good job of it. With our emergent qualities of self-awareness, intelligence, speech, science, technology, and dogs-don't-eat-dogs morality, we are not just bursting a bacterial cell, we are bursting the planet.

It's important to know where we came from. And where we are going.