RESUMO
Microcin C51 is a small peptide antibiotic produced by Escherichia coli cells harbouring the 38 kb low copy number plasmid pC51, which codes for microcin production and immunity. The genetic determinants for microcin synthesis and immunity were cloned into the vectors pBR325, pUC19 and pACYC184. Physical and phenotypic analysis of deletion derivatives and mutant plasmids bearing insertions of transposon Tn5 showed that a DNA fragment of about 5 kb is required for microcin C51 synthesis and expression of complete immunity to microcin. Partial immunity can be provided by a 2 kb DNA fragment. Mutant plasmids were tested for their ability to complement Mic- mutations. Results of these experiments indicate that at least three plasmid genes are required for microcin production. The host OmpR function is also necessary for microcin C51 synthesis.
Assuntos
Bacteriocinas/biossíntese , Escherichia coli/genética , Antibacterianos/biossíntese , Bacteriocinas/genética , Clonagem Molecular , Elementos de DNA Transponíveis , Escherichia coli/metabolismo , Genes Bacterianos , Teste de Complementação Genética , Mutagênese Insercional , Plasmídeos , Mapeamento por Restrição , Deleção de SequênciaRESUMO
A screening of 11956 enterobacteria isolates resulted in selection of seven active microcin-producing strains. The microcins were shown to be peptides or their derivatives with a rather broad spectrum of activity, mainly against Gram-negative bacteria. According to cross-immunity criteria, the microcins studied belonged to two of the previously suggested types, B (five strains) and C (two strains). Those of type B could be further classified into two subtypes on the account of differences in the spectrum of antibacterial activity. In five cases out of seven the microcin-producing ability has been attributed to plasmids that the strains harboured. The effect of microcins on sensitive cells was shown to depend on ompR and ompF gene products.