Ocean bug has 'smallest genome'

BBC ^ | 8/19/05 | Roland Pease

[AdmSmith]

What is more, Pelagibacter has none of the genetic clutter that most genomes have accumulated over time. There are no duplicate gene copies, no viral genes, and no junk DNA.

Very few bacteria have "junk" DNA or viral genes or duplicate gene copies (probably due to selection pressure), so that is no surprise. "Junk" DNA are of various types and we probably have to live with the use of this term for a long time, even in Science http://www.sciencemag.org/content/vol309/issue5738/twis.shtml .

I wonder when this record (1,354 genes)will be broken; next year?

[Old Professer]

I ain't listening to no peg-legged bacterium.

[contemplator]

..why other genomes have accumulated so much apparently random stuff, if there is some genetic advantage to be gained from this streamlining.

Of course this idea implies some sort of species conciousness going on during the cellular formation stage and will no doubt attract criticism from everyone but hey, wild thoughts have their place too...

As in the case of the whale, in the event that things don't turn out to be as advantageous on land as you would like, you have the ability to revert much faster if you have saved the codes for the appropriate cellular engines. This ability to "devolve" in a rapid fashion might come in handy should your species suddenly need to survive another ice age.

[js1138]

"so many" = all

At least all biologists publishing original research.

[js1138]

I knew there was a practical reason for never throwing anything away.

[AndrewC]

My goodness...

Where is all the "junk" demanded of a "random" unthinking process? Or is any change an immediately fatal one?

[RightWingNilla]

Its not the size of the genome but how you splice it.

[RightWingNilla]

I thought it was typical for prokaryotes to have very streamlined genomes with little/no unused DNA?

[jennyp]

As for the JennyP theory, that's part of what I was getting at: if there's a forcing function toward "thriftiness," it seems that the accumulation of "buffers" in the middle of a genome shouldn't happen.

It seems the function is very forceful indeed! I've never heard of a species actually favoring some bases over others because of the incrementally higher metabolic cost:

The spareness of its genome is related to its frugal lifestyle. The shorter the length of DNA that needs to be copied each generation, the less work there is to do.

Pelagibacter has even gone one step further. It has chosen where possible to use genetic letters - or base pairs - which use less nitrogen in their construction: nitrogen is a difficult nutrient for living things to obtain.

(me to Pelagibacter: "Dude, that is extreme!"

Something occurs to me: In larger populations, natural selection plays a more significant role than in smaller populations. That's why biologists talk about genetic drift being more significant players in speciation, as the small breakaway population gets isolated from the bigger parent population.

So if these "estimated 20 billion billion billion" Pelagibacters are spread out all across the oceans, that's one huuuuuge population. Neutral mutations would have no chance at all to spread across the population, let alone even a minisculely harmful mutation. So any genetic innovation, which might survive in a small founder population long enough to develop into something positive, would never get the chance to start the experiment.

[LiteKeeper]

YEC INTREP

[furball4paws]

The way you define things is of importance here. Procaryotes are certainly much more streamlined and have, typically, some "junk DNA" (is it really "junk"?).

However, some bacteria carry incredible amounts of baggage. Some Pseudomonas species can use over 200 different chemicals as sole source of carbon and energy. That entails carrying a number of genes around in good operating order should one run into one of these compounds that is rarely available. Other bacteria like Pelagibacter are highly specific and carry little extra information.

Two different solutions to life's problems. One adapts to eating a dilute soup that's unlikely to change (at least rapidly) and that there is a lot of. The other is able to adapt quickly to an influx of just about any carbon and energy source, but carries a lot of excess baggage in order to do it.

[furball4paws]

"So if these "estimated 20 billion billion billion" Pelagibacters are spread out all across the oceans, that's one huuuuuge population. Neutral mutations would have no chance at all to spread across the population, let alone even a minisculely harmful mutation. So any genetic innovation, which might survive in a small founder population long enough to develop into something positive, would never get the chance to start the experiment."

IOW it's setting itself up for extinction?

[jennyp]

"...So any genetic innovation, which might survive in a small founder population long enough to develop into something positive, would never get the chance to start the experiment."

IOW it's setting itself up for extinction?

I dunno about that. But natural selection is more dominant in large populations than in small ones, and so it overwhelms the action of genetic drift.

So I think they're not setting themselves up for extinction, but they are preventing themselves from ever making any major evolutionary changes. They'll always remain nothing more than the best Pelagibacters they can possibly be.