The vermin only teaze and pinch
Their foes superior by an inch.
So, naturalists observe, a flea
Has smaller fleas that on him prey;
And these have smaller still to bite ‘em,
And so proceed ad infinitum.
What’s the most common living thing on Earth? A smart guess would be to start with bacteria, which make up over half of all biomass on Earth (you did watch that episode of my YouTube show, right?). And since the oceans cover considerably more than half the planet, a marine bacterium would also make sense.
Until very recently, almost everyone with an opinion on these things would agree. See that bacterium in the electron microscope image above? It’s called Pelagibacter ubique, an ocean-dwelling microbe whose family of relatives make up a stunning one-third of aquatic life forms (by sheer numbers). Why so numerous? One popular theory was that because they are immune to infection by bacterial viruses, they could grow unchecked.
Thanks to some creative science, that theory now appears dead wrong (here’s the paper in Nature). By diluting seawater over and over (that is what grad students are for), Stephen Giovannoni’s team was able to isolate single ocean viruses, most of which had never been identified before. Then they stuck them in with P. ubique and waited. Amazingly, some of the viruses could infect this previously uninfectable bacterium! Those little blobs in the image above are actually viruses ready to burst out of their unfortunate little host.
They sequenced the DNA of those viruses, when back to the ocean, and found that one of them, with the unremarkable name “HTVC010P”, is … well, basically everywhere.
This “smaller flea”, which itself feeds upon something so mind-bogglingly numerous, is now our best candidate for “The World’s Most Abundant Thingy”.
Whether or not it’s a life form? I’ll leave that up to you …