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Integration of F’lac plasmid into chromosome of both gyrA(Ts) and gyrB(Ts) cells phenotypically suppress the thermosensitive mutations of the DNA gyrase enzymes. As the comparative strains isolated from dnaA(Ts), these high frequency of recombination (Hfr) derivatives were able to transfer chromosomal markers to recipient strains, showed a growth rate of about 60 min, and developed filamentous forms when incubated at the temperature of 43°C. Conversely to dnaA(Ts) Hfr selected isolates, the great majority of Hfr derivative of gyrase mutants resulted resistant to acridine orange and rifampin. Time-kill experiments carried out at the non-permissive temperature also revealed that nalidixic acid has no antibacterial activity on these Hfr strains while derivatives of dnaA(Ts) mutant, as well as the control strain HfrH, were strongly inhibited by this drug. Therefore F plasmid induced duplication of chromosome in the mutants even if the DNA gyrase enzymes are not working. Of a certain interest is that these bacteria exhibit physiological perturbations that affect the main cellular functions, however, they do not appear essential for the survival of the strains.
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