The main bacterium they study, Pelagibacter ubique (pelagi = ocean, bacter = bacteria, ubique = everywhere (ubiquitous), is the most popular member of a larger group of bacteria called SAR11. I can give you all the statistics or you can believe that it's given scientific name is true and that there are more of them than anything else in the ocean. Anyways, a funny thing some people noticed since this bacterial group was described, was that there didn't seem to be any bacteriophages (bacterio = bacteria, phage = to consume) associated with it...
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| From BIOS Oceanic Microbial Observatory |
You may think, Well they are quite small for bacteria so maybe they just avoid encountering phages or Maybe being incredibly minute makes P. ubique hard to infect? But no no no, there are so many of them out there and there are others of similar size with plenty of phages that eat away at them...
Well, rest easy folks, they found them! Now we know it's not that SAR11 has magic anti-infection powers. It's just that no one has found them until now. These researchers did an ingenious study, the methods of which are concisely explained in this Economist piece. They used P. ubique and found it does indeed have phages - and since their are lots of P. ubique (and their SAR11 cousins) out there, there are lots of their phages too. How might this work?
Remember the mid-14th century? Under plague conditions, people whose immune systems could not handle infection died in the masses, taking their genes with them. Those with the fortunate cocktail of immune genes would survive the outbreak, have babies, and continue the human race. A very dramatic case of natural selection. Why am I talking about the Black Death? Why, to bring up The Red Queen Hypothesis. This evolutionary theory (RIP Leigh Van Valen) posits that "it takes all the running you can do, to keep in the same place." And so, immunity traits must keep changing and evolving in order for its host to stay one step ahead of parasites and pathogens. Humans recombine genes during sex and make a kid. Way to go for the kid but the parents are still stuck with the same genes they were born with for the rest of their life -> bummer! Bacteria don't play that. They can swap DNA with each other (conjugation) or just absorb it from the environment around them (transformation)! What a wild and crazy world, huh? As you would imagine, this means a community of bacteria can evolve to adapt rapidly to stressful conditions. And that is exactly what this paper suggests. They suggest that rapid* coevolution in the SAR11 group in response to phage predation has helped lead them to successful dominance of the ocean!
It will be very interesting to see what new research comes of this discovery. Being one of the most abundant things out there in the marine landscape, SAR11 plays a huge role in the microbial food web and in regulating geochemical cycles.
* the Nature article also mentioned studies in which they found recombination rates in the SAR11 group were also freakishly high!
Zhao Y et al. Abundant SAR11 viruses in the ocean. 13 Feb 2013. Nature <http://www.nature.com/nature/journal/vaop/ncurrent/full/nature11921.html>
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