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. -Jonathan Swift 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 …
Pop-upView Separately

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.

-Jonathan Swift

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 …

Coming of Phage

Everything you’ve been taught about phage is wrong. Well, maybe not everything. Heck, maybe you’ve never been taught anything about phage in the first place! But if you’ve ever encountered a story about this family of bacteria-infecting viruses, I’m willing to bet it included a picture much like this:

image

That geometric lunar lander is the standard illustration of phage such as T7. It looks exotic and alien, a freakish example of biological symmetry, but it’s pretty true to the actual biology: The icosahedral protein head, the protruding neck that it uses to pierce the membrane of its victim so that it can inject its genetic material … and the legs.

Wait a sec, those legs need revising. Some really cool new research by Ian Molineux (who taught my graduate school molecular bio class, btw) says that all those “legs-out”, moon lander drawings of phage probably aren’t right.

In the video above you see that, according to the electron imagery they report in their Science paper, those legs stay tucked up next to the body for most of the free-floating life of the phage. It sort of drags one or two along, waiting to hook onto an appropriate bacterium that it can infect, at which point it extends the rest of the legs to go into full infection mode. To give you an idea of how hard this was to observe, a single phage is only around 20-30 nanometers wide, which means you could fit about 4,000 of them across the width of a single human hair!

It might seem like a small, ho-hum tidbit of research at first, since who really cares about a virus that infects bacteria? But phage are incredibly important. Phage have driven a great deal of the evolution of life on Earth. They are vehicles of gene swapping that have allowed genomes to expand and become more complex. They are veterans of 70+ years of biology research, from back when we first identified DNA as a genetic material to today’s exotic synthetic biology applications. A great deal of what we know about molecular genetics is because of these little guys, and we’re still making the most basic discoveries as to how they function.

Never let anyone tell you that there’s nothing left to discover! We have scarcely begun to fill in the colors, even for the most basic parts of biology’s palette. 

Bacteria-Killing Viruses Wield an Iron Spike Tiny warfare involves tiny weapons. Now a group of biologists has finally described the tiny spike that a bacteriophage uses to invade its bacterial victims. Bacteriophage are likely the most abundant biological entity on Earth. We know that any scoop of sea water or soil will have billions of bacteria in it. But just like the abundance of viruses that surround humans every day, these bacteria are vastly outnumbered and warding off phages, bacterial viruses. At the bottom of their angular heads is a long protein shaft that they use to deliver their DNA into their victim. A new structure has been determined showing an iron-tipped spike at the tip of the shaft, almost like a nail to pierce the bacterial membrane. (via ScienceNOW, images from Cell Press)
Pop-upView Separately

Bacteria-Killing Viruses Wield an Iron Spike

Tiny warfare involves tiny weapons. Now a group of biologists has finally described the tiny spike that a bacteriophage uses to invade its bacterial victims.

Bacteriophage are likely the most abundant biological entity on Earth. We know that any scoop of sea water or soil will have billions of bacteria in it. But just like the abundance of viruses that surround humans every day, these bacteria are vastly outnumbered and warding off phages, bacterial viruses.

At the bottom of their angular heads is a long protein shaft that they use to deliver their DNA into their victim. A new structure has been determined showing an iron-tipped spike at the tip of the shaft, almost like a nail to pierce the bacterial membrane.

(via ScienceNOW, images from Cell Press)

Source: news.sciencemag.org