An alternative mechanism of action of microcin J25 in Escherichia coli strains

VINCENT, PAULA A.; BELLOMIO, AUGUSTO; ARCURI, BEATRIZ FERNANDEZ DE; FARÍAS, RICARDO N.; MORERO, ROBERTO D.; SALOMÓN, RAUL A.

San Carlos De Bariloche, Argentina.

Congreso; Bariloche Protein Symposium. Saib XXXIX Annual Meeting. Sab XXXII Annual Meeting.; 2003

Sociedad Argentina de Biofísica y Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

By using serial dilution assays we have observed striking differences in sensitivity to microcin J25 (MccJ25) between E. coli strains. We have previously established that RNA polymerase (RNAP) is the target of MccJ25 and that the antibiotic inhibits transcription in vivo and in vitro. E. coli strain SBG231 harbors a mutation in rpoC (the gene encoding largest subunit of RNAP) which makes this strain completely resistant to the antibiotic. The mutation was transduced to the MccJ25-hypersusceptible strain AB1133. One of the transductants, named PA232, was studied further. Transfer of the mutation was confirmed by genetic complementation tests and in vivo transcription experiments. Notably, strain PA232 did not become completely resistant to MccJ25. This could be explained by assuming the existence in strain AB1133 of an alternative mode of action of the antibiotic, which would not be operative in strain SBG231. This result could also explain the differential sensitivity of E. coli strains. Previous work from our laboratory showed that in Salmonella strains MccJ25 acts on the cytoplasmic membrane by dissipating the electric potential and affecting the cell respiration. In the present study we have not detected an effect on cell respiration in PA232. However, the possibility that the membrane be the putative second target in hypersusceptible E. coli strains cannot be discarded.