Viruses and Bacteria -- Flagellum

	http://people.csail.mit.edu/jaffer/GTOL/flagellum
	Viruses and Bacteria -- Flagellum

On The Origin of Collectives -- Bacterial Evolution dealt mostly with finite bacterial communities not continually invaded by other species. A virus must be exceptionally non-virulent or have vanishingly small potency in order to be a stable participant in that community's equilibrium.

But in very large fluid environments like rivers, lakes, and oceans thousands of species are constantly in flux. With seasonal, climactic, and geological changes, the conditions are infrequently stable for long enough durations for all the individuals of all species to acheive Nash equilibrium.

Without equilibrium, bacterial strains can gain temporary advantage from unrestrained division. Such plentiful stocks of microbes are ripe for predation. It has recently come to light that the most significant predators limiting bacterial populations may be bacteriophages.

Viruses

In "All the World's a Phage" ([8]) John Travis writes:

These plentiful viruses could have a profound impact on their environment, especially in water. According to estimates put forth by Suttle, phages destroy up to 40 percent of the bacteria in Earth's oceans each day. In doing so, bacteriophages may influence the oceans', and perhaps the entire world's food supply by limiting the volume of bacteria available for other organisms to eat. Bacteria destroyed by phages fill the water with organic matter that's either consumed by other bacteria or settles to the ocean floor.

The article asserts there may be 10 bacteriophages for every bacterium on the planet, making them Earth's major life form. Some viruses carry genes for proteins which help the infected bacterium survive longer (thus making more phages). Phages carrying 700 genes, more than most bacteria, would seem capable of reprogramming a bacterium completely.

What are the essential properties of viruses?

enclosed by radially symmetric, self-assembling capsids;
contain DNA or RNA encoding genes for production of capsids; and
contain DNA or RNA encoding genes which override and usurp host gene regulation to produce viruses.

Bacteriophage M13

E. Coli flagella
Looking at bacteriophage M13, it bears an incredible resemblance to an E. Coli flagellum. Is this coincidence? I think not.


Bacteriophage M13

E. Coli flagella

The virions produced in an immobile bacterium will tend to infect fewer new hosts than virions produced by bacterium that move, even a short distance. Near the end of viral replication, with virion helices protruding through its membrane, motion of those helices moves the infected organism; thus improving the viral potency. Thus viruses will tend to evolve movement of nearly completed helices.

Viral genetic replication (like all replication) is prone to errors. So mutant virions will arise. Some of these mutants will code correctly for the capsid protein and its movement, but code incorrectly the other parts of the viral genome. With the mutant's genes incorporated into the bacterial chromosome, a flagellum is born!

After writing the explanation above I was surprised to discover that a pseudo-science discipline called intelligent design has been founded by those lacking the perspicacity to see the connection between filamentous bacteriophages and bacterial flagella.

To recap:

Many species of virus have long helical capsids made of self-assembling proteins.
Some of these virus species embed proteins in their host's cell membrane which force the helical capsids through the membrane.
The force which moves the capsids also acts to move the membrane in the opposite direction.
Movement of an infected host slightly improves the chance of the new virus particles reaching unifected cells.
Such viruses will tend to evolve into flagellating forms.
When such a virus'es partial genome becomes incorporated into a host, the helical capsid proteins and motile machinery become part of the host.
This process will have occurred as long as bacteria and their phages have existed, even now.
Thus the genes for bacterial flagella will be unrelated (not sharing common sequences) between many species.

I am a guest and not a member of the MIT Computer Science and Artificial Intelligence Laboratory. My actions and comments do not reflect in any way on MIT.
		The Game Theory of Life
	agj @ alum.mit.edu	Go Figure!