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Mechanisms Of Sex In Escherichia Coli

656 words - 3 pages

The discovery of the gene transfer mechanisms could be attributed by the work of Lederberg and Tatum back in 1946. Using Escherichia coli(E.coli) as their model, they proposed the genetic materia of E.coli could be exhanged via sexual process. In order to prove their hypothesis, they mutated 2 wild type E.coli strains(K12) using X-ray or ultra-violet radiation to produce Y-10 and Y-24 mutant strains. The former was auxotrophic to threonine, leucine and thiamin whereas the latter failed to produce biotin, phenylalanine and cystine[1]. These mutant could only survive in mininal media plates provided that the aforementioned amino acids are supplied accordingly to each mutant strains.

Further experimentation was conducted where they mixed those two mutant strains together and something bizarre was observed. They observed colony growth on the third minimal media plate where the E.coli present on that plate bahaved exactly like the wild type(K-12) prototroph strain. Since no colonies grew on the first two plates, it was deduced that the colonies on the third plate could not be the result of reverse mutation as the spontaneous mutation rate was exceedingly small. Thus, Lederberg and Tatum suggested two possible interpretations for the sex mechanisms of E.coli viz. transformation and conjugation. The former would imply the presence of unknown transforming factors which brought about gene mutations that caused the reversion of mutant E.coli strain to wild type strain. The latter would then suggest that random gene reassortment in new combinations which required the fusion of bacterial cells in order to exchange genetic substances. Regrettably, no further evidences were produced to substantiate either one of these models.

In the BIOL2202 bacteria genetics practical, our results can hardly discriminate which sex mechanism was employed by E.coli to revert back to prototroph as the donor(JC158) and recipient strands(AB1157) were added into a Erlenmeyer flask and mixed together to facilitate conjugation. Besides, the reversion could also be attributed to transformation due to unknown transforming factors which somehow mutated the gene back to...

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