A genetic analysis of colicin E2 sensitivity in Escherichia coli K-12.
thesisposted on 19.11.2015, 08:53 by Roger Stuart. Buxton
This Thesis has investigated the genetic nature of the sensitivity of the bacterium Escherichia coli K-12 to the anti-bacterial protein, colicin E2. Particular attention has been paid to a group of E2-tolerant mutants, termed Cet-, since previous reports by other workers had shown that some cet mutations were pleiotropic, affecting a wide range of properties of the cell envelope. A genetic analysis has also been undertaken of Bfe- mutants, which differ in that they are resistant to all the E-group colicins because of a failure in colicin adsorption. The location of the cet gene has been determined, the gene order deduced being: dna-7D - dra - drm - serB - trpR - cet - thr, whereas previous reports located cet to the left of serB. Bfe mutations, comprising one complementation group, have been shown to map at a separate location, the gene order being metB-arg(ECBH)-bfe-thi-metA. In contrast to previous reports, none of the pleiotropic properties of Cet- mutants tested mapped near the cet locus. Thus, in two Cet- strains, UV-sensitivity derived from a Ion mutation; in another, UV-sensitivity mapped near the recA locus; in a third, resistance to phage T4 was shown to map at a position distinct from cet. The cet- allele was dominant to wild-type, whereas bfe- was recessive. The effect of different genetic backgrounds upon the expression of E2-tolerance in Cet- mutants has been examined. In particular, recA and recB mutations reduced E2-tolerance. An investigation of one of the pleiotropic properties of certain Cet- strains, resistance to phage ?, revealed it to be due to poor adsorption of the phage. Lastly, it has been foimd that E2-directed DNA degradation proceeds normally in some strains deficient in endonuclease I, and no evidence could be found that DNA degradation and inhibition of cell division induced by E2 are separate uncoupled processes.