Mike PSS
Posts: 428
Joined: Sep. 2006
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| Quote (avocationist @ Jan. 29 2007,15:09) | | Quote | I'd be very interested in your source which states that any mutation is specifically directed. I am aware of papers that show an increased mutation rate under certain stress situations (such as application of antibiotics), which would naturally lead to a faster rate of "finding" an antibiotic resistance mutation. But I am not aware of any that show specifically directed mutations in bacteria.
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It gets turned on in response to the environment, is confined to speific loci in the genome, and is turned off when it's job is done. The mutations which occur under those conditions are random. Thus it took (if I understood the article) 3 months to produce the nylon eating mutation(s) but apparently that was not the only time it occurred. Spetner mentions it being discovered accidentally 30 years after nylon was invented. |
I missed this one.
Avo,
Are you referring to the second-to-last paragraph in the nylon bug article where it states... | Quote | | Though a molecular basis for the emergence of nylon oligomer metabolism in PAO5502 is still unknown, it is probable that the basic mechanisms acting during environmental stress are involved in this adaptation. Recently, it was reported that simple polymerase errors increase in the adaptive mutation from Lac2 to Lac1 in E. coli (2, 17) and that molecular mechanisms by which adaptive mutation occurs include recombination (4). Lenski and Mittler have observed a 10,000-fold increase in Mu element excision due to starvation (10). Since the nylon oligomer has no detectable toxicity toward microorganisms, the wild-type cells could be maintained in a starved condition for a long period. After the cells accumulated the required genetic alteration to make a cryptic region active, cells grew in the nylon oligomer medium. The high frequency (1023) of the hypergrowing mutants of parental strain PAO1 on medium containing Ahx might be a result of a high mutation rate under the condition of starvation. |
The paper is making a claim based upon previous observations. The increased mutation rate occurs due to starvation of the bug. There is no "switch" or "selection" that occurs because of this starvation condition. There is only inferred mutation rate increase based upon conditions that resemble past experiments and observations. Argy's response supports this claim.
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