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  Topic: Evolution of prokaryote flagella, Links to discussions, webpages, refs< Next Oldest | Next Newest >  

Posts: 319
Joined: May 2002

(Permalink) Posted: May 07 2003,05:15   

Another reply from here:

Nelson writes,


With respect to adhesion organelles, I dont have time to tread though an entire thread to find an example of a flagellum acting as an adhesion organelle, but something tells me that you are just talking about a pilus, which I already discussed. My reason for thinking this is that since this was brought up in the immunity thread, PapD of the pilus has Ig-like domains. It is misleading to call pilus "bacterial flagellum".

I'm not sure what you're talking about with a pilus, although a great many (most?) pili of various kinds do have adherence as their function or one of their functions.

My point is that it appears many flagella also have an adhesion function.  The paper I was referring to from the immune system thread was the first paper I cited on page 1, sorry that wasn't clear:

Giron JA, Torres AG, Freer E, Kaper JB. The flagella of enteropathogenic Escherichia coli mediate adherence to epithelial cells. Mol Microbiol 2002 Apr;44(2):361-79

There are others, e.g.:

Gavin R, Rabaan AA, Merino S, Tomas JM, Gryllos I, Shaw JG. Lateral flagella of Aeromonas species are essential for epithelial cell adherence and biofilm formation. Mol Microbiol. 2002 Jan;43(2):383-97  

One more:

de Oliveira-Garcia D, Dall'Agnol M, Rosales M, Azzuz ACGS, Martinez MB, Girón JA (2002).Characterization of Flagella Produced by Clinical Strains of Stenotrophomonas maltophilia. Emerging Infectious Diseases [serial online]


Although adherence to abiotic surfaces is a property of both environmental and clinical S. maltophilia isolates, little information has been available to elucidate the nature of the surface factors involved in this phenomenon. Flagella have been associated with biofilm formation in other bacteria (18,20–22), where they can perform three basic roles: a) act as an adhesin promoting intimate attachment to the surface; b) generate force to subjugate the repulsive forces between bacteria and surface; and c) promote spread of the bacteria throughout the surface (20).

I bring it up because the question is whether or not intermediate stages had selectable function.  It appears that an adhesive pili is one example of such a selectable intermediate stage, even though it wouldn't need motors or motility function.  

Based on the above quote, we might even put forward a hypothesis: a certain species of bacteria living in a pre-flagella world makes its living by adhering to particles (bits of silt or whatever).  When it reproduces, brownian motion spreads it a small distance in a random direction before it grows its primitive Type III pili and adheres to another silt particle.  Occasional disturbances (such as waves or tides or new silt layers) wipe out most of the population at regular intervals, creating a classic early-successional ecological system (think weeds in a continually disturbed field).

Amongst the typical huge number of detrimental mutations that go nowhere in this population, a very small proportion of the mutations cause a member of the population to have a mutant ExbB homolog that attaches to the base of the pili rather than whatever it was originally attached to.  This serves only to give random, undirected motion.  However, experiments even with bacteria with partially-disabled flagella or flagella stuck on "tumble" show that they have diffusion coefficients orders of magnitude higher than dead or otherwise immotile bacteria (which still have diffusion coefficients large relative to body size).  So, even undirected motility will serve to increase diffusion-distance-before-sticking, allowing that genotype to spread further and faster than the rest of the population (mechanisms to increase random diffusion of offspring are ubiquitous in life BTW, think dandelion seeds and go from there).  Thus, this mutation comes to dominate and we have our very primitive proto-flagellum.  Only gradually does all the fancy stuff get added -- finer co-adaptation of rotor and motor, chemotaxis sensors, switching, hook/flagellin distinction, etc.

Hmm, don't think that Dembski took anything like this into account in his calculation.

  46 replies since Nov. 28 2002,22:50 < Next Oldest | Next Newest >  

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