Stepwise formation of the bacterial flagellar system [merged]

[chrisharrison]

Date of publication? Today.

Elucidating the origins of complex biological structures has been
one of the major challenges of evolutionary studies. The bacterial
flagellum is a primary example of a complex apparatus whose
origins and evolutionary history have proven difficult to reconstruct.
The gene clusters encoding the components of the flagellum
can include >50 genes, but these clusters vary greatly in their
numbers and contents among bacterial phyla. To investigate how
this diversity arose, we identified all homologs of all flagellar
proteins encoded in the complete genome sequences of 41 flagellated
species from 11 bacterial phyla. Based on the phylogenetic
occurrence and histories of each of these proteins, we could
distinguish an ancient core set of 24 structural genes that were
present in the common ancestor to all Bacteria. Within a genome,
many of these core genes show sequence similarity only to other
flagellar core genes, indicating that they were derived from one
another, and the relationships among these genes suggest the
probable order in which the structural components of the bacterial
flagellum arose. These results show that core components of the
bacterial flagellum originated through the successive duplication
and modification of a few, or perhaps even a single, precursor
gene.


Here's the link:
http://www.pnas.org/cgi/reprint/0700266104v1

[Vicious Love]

Irreducible flagellum, we hardly knew ye. Well, on to the next "You don't know for sure exactly how it happened, so God did it" argument.

[Boro Nut]

Irreducible flagellum, we hardly knew ye. Well, on to the next "You don't know for sure exactly how it happened, so God did it" argument.

I thought the argument was more along the lines of 'Just because it could have evolved doesn't mean it did. Probably. No, it's nice of you to ask, but I don't think I would care to define probably. And who said anything about God? Just because it is God really it doesn't mean it has to be. It could be any God. Or not God even. Just as long as it really is God. Our God. Apologies for all the scientific jargon there.'

Boro Nut

[Vicious Love]

I thought the argument was more along the lines of 'Just because it could have evolved doesn't mean it did. Probably. No, it's nice of you to ask, but I don't think I would care to define probably. And who said anything about God? Just because it is God really it doesn't mean it has to be. It could be any God. Or not God even. Just as long as it really is God. Our God. Apologies for all the scientific jargon there.'

You're pretty good at this. Have you considered prefixing "Dr." to your name?

[The Path of Needles]

I hope IDers stop using that weak flagellum argument now. Knowing them they won't.

[espritch]

Well, not to worry. There are still plenty of gaps for the IDists to hide their intelligent designer in.

But I find this article rather providently timed given some of the current threads in the forum. It's almost like some invisible all powerful entity wants to make the IDists look like idiots. It's almost enough to make me believe in God.

[RBH]

A list I'm on with a couple of flagellum experts is dubious about aspects of that paper. I'm going to withhold comment until I hear more from them.

RBH

[RBH]

OK, here's the first public critique (http://www.pandasthumb.org/archives/2007/04/flagellum_evolu_1.html) of the paper. It doesn't come out looking real strong, certainly not as strong as the paper's authors seem to believe.

RBH

[chrisharrison]

Thanks for the link RBH. I sent an email to PT earlier about it, and I'm glad Nick Maztke got a critique of it up so quickly.

[RBH]

Thanks for the link RBH. I sent an email to PT earlier about it, and I'm glad Nick Maztke got a critique of it up so quickly.That list was humming for some hours. :)

RBH

[chrisharrison]

So any plan of action?

Can you contact PNAS to express your concerns with the paper, or is something set in stone once it's published?

[Boro Nut]

I hope IDers stop using that weak flagellum argument now.

Yeah. I mean, what good is a weak flagellum? Anyone with half an eye should have spotted that problem.

Boro Nut

[rossum]

You're pretty good at this. Have you considered prefixing "Dr." to your name?
He can't do that until he has sent the cheque for $100 to FlyByNight University, PO Box 427, Podunk, Idaho.

rossum

[Peez]

With all the silly attacks on the evolution of flagella, perhaps this article is of interest:Stepwise formation of the bacterial flagellar system
Renyi Liu, and Howard Ochman
doi:10.1073/pnas.0700266104
published online Apr 16, 2007; PNAS
This information is current as of April 2007.

Elucidating the origins of complex biological structures has been one of the major challenges of evolutionary studies. The bacterial flagellum is a primary example of a complex apparatus whose origins and evolutionary history have proven difficult to reconstruct. The gene clusters encoding the components of the flagellum can include >50 genes, but these clusters vary greatly in their numbers and contents among bacterial phyla. To investigate how this diversity arose, we identified all homologs of all flagellar proteins encoded in the complete genome sequences of 41 flagellated species from 11 bacterial phyla. Based on the phylogenetic occurrence and histories of each of these proteins, we could distinguish an ancient core set of 24 structural genes that were present in the common ancestor to all Bacteria. Within a genome, many of these core genes show sequence similarity only to other flagellar core genes, indicating that they were derived from one another, and the relationships among these genes suggest the probable order in which the structural components of the bacterial flagellum arose. These results show that core components of the bacterial flagellum originated through the successive duplication and modification of a few, or perhaps even a single, precursor gene.link (http://www.pnas.org/cgi/reprint/0700266104v1)

Peez

[Jet Black]

great paper. Pretty complicated, but it's a fascinating read. I had no idea that there was so much diversity in an organelle that is allegedly so fine tuned.

[Oolon Colluphid]

Ah, looks like you guys missed where RBH pointed to Nick Matzke's PT comments (http://www.pandasthumb.org/archives/2007/04/flagellum_evolu_1.html) on the paper, which seems to be... not all we might hope for ;).


Here's Nick's update (http://www.pandasthumb.org/archives/2007/04/update_on_pnas.html) on it.
I conclude that FliC and FliI are not homologous. Therefore not all core flagellar proteins are homologous. Therefore they didn’t come from a single ancestral ur-flagellar gene. Therefore the conclusion of Liu & Ochman is wrong. Case closed.

[chrisharrison]

And I already posted about this a few days ago here:
http://www.iidb.org/vbb/showthread.php?t=203949

[Oolon Colluphid]

And I already posted about this a few days ago here:
http://www.iidb.org/vbb/showthread.php?t=203949
Thanks Chris, couldn't think what to search on that wouldn't pull up countless flagellum mentions! Merging...