Moselio Schaechter

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March 03, 2011

Talmudic Question #72

Suppose a marine bacterium evolved the perfect phage defense, one that no phage could overcome. A thousand years hence, what changes would you expect to see in the marine microbial community?


I have two words for you: Maginot Line. A perfect defence against Germans. Turned out not to be, of course, but in any case, what about against the British?

May be it would not induce any outcome significantly. Transfer of genetic material can be done since bacteria can produce plasmid and use pilus to make transformation.
However, I don't think the perfect phage defense would help to incerase the bacteria population a lot. As it is mentioned, phage is not the only predator of bacteria. It may enhance the amount of others predator of the bacteria in a little bit.
I think that the situation after thousand years would remain unchanged in the marine microbial community, but in biology ^^

No change, and not a one of the critters to be found, nohow. The other microbes would happily move into its niche as the niche, itself, wanders idly off, leaving these slow-adapting, ineducable throwbacks to fade quietly into history.

That is a rather unfeasible starting point for nature. No organism is obliged to be absolutely perfect in any biological trait. Instead, it is sufficient to achieved an evolutionary trade-off... that allows some temporal truces in the middle of the armament races. The history of cell networks is to confer robustness to the system with redundant (and paranoid)countermeasures. I envision that the only effective way to protect the intracellular systems from viral sabotage is to reduce its complexity and erase components. So, taking into account the reduction hypothesis for the origin of viruses, I think these organism should be a parasite... I propose that after some million of years, that prokaryote will evolve... into a virus. Maybe a mimivirus.

Alberto Carmona.

The changes to be found would had derived, among other things on,

1st: How hungry and "angry" the variety of bacterivorous protozoans, crustaceans and other bacteria-consuming life forms would have been during that millenium.

2nd: The "level of genetic stupidity" the offspring of this marine bacterium could have been able to carry on generation after generation. Most probably natural selection would have wiped out such a "phage genetically isolated organism" that had not been able to take profit from the horizontal gene transfer that a variety of phages are responsible of.

If that bacterium could think (improbable considering the stupidity inherent to such a bacterium...) and would dream remaining "potentially alive", the best decission for it would have been going sleep inside a liquid nitrogen jar.

Francisco Torrella
University of Murcia, Spain
(Sorry for my English)

Well, Elio, I have to say that to borrow from Bob Dylan, the paradigms, they are a changin'. I well remember in college being taught that phages were interesting curiosities that surely had little impact on natural populations. Now we learn that marine phages have a pivotal role in ecosystems.

Just as bacteria develop resistance to phage, phage respond in kind, in a Red Queen kind of evolutionary arms race. Darwinnowing of the protean variability of virus and host proceed apace. So I guess that I have trouble in believing in a SDI-style perfect resistance to bacteriophage.

But even so, I am pretty sure that other prokaryotes are excellent predators, and would be evolutionarily happy to expand their role in such a situation. Forest Rohwer's adage about the huge number of predatory entities in a few milliliters of seawater is quite apt---and not just bacterial viruses are chomping away and shaping the community structure.

As for paradigm shifts, I am reminded of this:

There are four stages of acceptance of new ideas: i) this is worthless nonsense; ii) this is an interesting, but perverse, point of view; iii) this is true, but quite unimportant; iv) I always said so.
-J.B.S. Haldane, Journal of Genetics volume 58, page 464 (1963).

As always, I enjoy these Talmudic Questions. I think that you should lead a discussion of one or two of them in this class of yours at UCSD/SDSU, and tape it for Microbe Video! Such a situation is where true learning will take place.

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