Regions associated with the stable maintenance of plasmid pSC101 and its tetracycline resistance

Antibiotic susceptibility of Escherichia coli dnaK and dnaJ mutants

The role of two chaperone proteins, DnaK and the cooperating factor DnaJ, in Escherichia coli antibiotic susceptibility to three antibiotics (a beta-lactam, chloramphenicol, tetracycline) has been studied. It was found that null dnaJ and dnaKdnaJ mutants are impaired in the functions leading to antibiotic susceptibility. The secretion of beta-lactamase to the periplasmic space is diminished in both mutants, and the additive effect of the two mutations was observed. The activity of chloramphenicol acetyltransferase is also impaired in an additive manner in both mutant strains. Tetracycline uptake is changed only in the double deletion mutant. These defects were observed only during incubation at high temperature (42 degrees C). Efficient complementation of some of these defects by the wild-type alleles introduced on low-copy number plasmid was achieved. Minimal inhibitory concentrations and the titer of the wild-type strains, delta dnaJ and delta dnaKdnaJ mutants treated with ampicillin, chloramphenicol, and tetracycline were also determined. Higher susceptibility of both mutants to chloramphenicol and tetracycline, as compared to their wild-type parent, was observed only after 1 h preincubation of cultures at 42 degrees C. On the contrary, both mutants were less susceptible to ampicillin than their parent strain.

Genetic relatedness of the basic replicon of the virulence plasmid in shigellae and enteroinvasive Escherichia coli

The regions required for replication (Rep) and for stable maintenance (Stb) of the 230 kilobase virulence plasmid, pMYSH6000, in Shigella flexneri 2a YSH6000 were identified on the restriction enzyme Sa/l fragments, C and O, respectively. The stable plasmid, pMYSH6610, consisting of adjacent fragments C and O was found to belong to the incompatibility group Fl. In all strains of shigellae and enteroinvasive Escherichia coli (EIEC) tested, virulence plasmids were found to be highly homologous with the Rep region of pMYSH6000. The restriction map of this probe was very similar to that of the inc region of RepFIIA replicon. The virulence plasmid of S. flexneri 6, S. boydii, S. dysenteriae and EIEC all coexisted stably with pMYSH6610, whereas that of S. flexneri other than serotype 6 and S. sonnei did not. These findings indicate that all the virulence plasmids of shigellae and EIEC are highly related but can be divided into at least 2 groups.

Plasmid pIMI38--the pBR322 derivative with increased stability in E. coli cells

Plasmid pIM138 which had been characterized by the higher resistance of its DNA replication to the action of clorobiocin in comparison with the progenitor plasmid, was tested for its stability in host cells in the absence of the antibiotic. Growing without selective pressure, pIM138 was better maintained in cells than pBR322. The stability in the presence and in the absence of clorobiocin can be unanimously assigned to the plasmid itself, but some influence of host cells cannot be excluded.

A series of Tn5 variants with various drug-resistance markers and suicide vector for transposon mutagenesis

A series of variants of transposon Tn5 were constructed by replacement of the 2.7-kb central segment which encodes kanamycin resistance with various other resistance-coding genes: tetracycline, chloramphenicol, gentamicin, trimethoprim, streptomycin or ampicillin. A thermosensitive replication mutant of the broad-host-range transmissible plasmid R388 was also constructed for use as a suicide vector for the delivery of transposable elements.