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The effects of mutator plasmids on the frequency of mutation to nalidixic acid resistance in Escherichia coli

Ambler, Jane Elizabeth; (1995) The effects of mutator plasmids on the frequency of mutation to nalidixic acid resistance in Escherichia coli. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

A 40 mDa R plasmid that encodes trimethoprim resistance was isolated from a nalidixic acid-resistant Shigella dysenteriae type 1 strain, and designated pYD01. pYD01 was found not to encode nalidixic acid resistance, but did carry a mutator function. It was shown to increase both reversion to histidine independence and the frequency of spontaneous and UV-induced mutagenesis of E. coli strain AB1157 to nalidixic acid resistance. pYD01-determined increases in mutagenesis were relatively small, but the plasmid-facilitated mutator effect was enhanced considerably by exposure to bactericidal concentrations of nalidixic acid. Plasmid R46, a control mutator plasmid, and RP4, which does not encode mutator function, did not affect the sensitivity of strain AB1157 to nalidixic acid, whereas pYD01 and R391 increased nalidixic acid sensitivity. pYD01 also sensitised strain AB1157 to UV in a manner analogous to R391. The UV-sensitising characteristics of pYD01 and R391 were found to be strain-dependent, since they protected Shigella sonnei, but not E. coli TK501 umuC uvrB against UV. The UV- sensitising effects of pYD01 and R391 were compared with those mediated by pGW16; sensitisation by the latter is known to be due to over expression of mutator genes. Post-UV survival studies of strain AB1157 carrying plasmids pGW16, pKM101, the parent of pGW16, R391 and pYD01 in single, double and triple combinations revealed that the post-UV effects mediated by pYD01 closely resembled R391, but were distinct from those of pKM101 and pGW16. Radiolabelled studies showed that plasmid R46, the wild-type parent from which pKM101 and pGW16 were derived, increased post-UV DNA synthesis in strain TK501, whereas pYD01 and R391 did not. This work confirms the hypothesis proposed by Crumplin (1987), that mutator plasmids can facilitate chromosomal mutagenesis to nalidixic acid resistance.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: The effects of mutator plasmids on the frequency of mutation to nalidixic acid resistance in Escherichia coli
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Health and environmental sciences; Acid; Escherichia; Mutation; Mutator; Nalidixic; Plasmids; Resistance
URI: https://discovery.ucl.ac.uk/id/eprint/10105132
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