Superoxide production would be a microcin J25 alternative mechanism of action in E. coli

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

Iguazú, Misiones - Argentina

Congreso; Saib XL Annual Meeting; 2004

de Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

    E. coli RNA polymerase (RNAP) is the intracellular target of microcin J25 (MccJ25). MccJ25 enters the cell after binding to a specific outer membrane receptor, FhuA. In Salmonella strains, MccJ25 acts on the cytoplasmic membrane affecting cell respiration. Previously, we obtained an RNAP mutant of  MccJ25-hypersusceptible strain AB1133 (PA232), which showed a residual sensitivity. This result may be explained assuming the existence of an alternative mechanism of action of MccJ25, which is investigated herein. Although we did not detect any effect on cell respiration in PA232, an important inhibition was found when this strain was transformed with  plasmid pGC01, carrying fhuA.     MccJ25 inhibits lactate and NADH dehydrogenase activities by 40% and 20 %, respectively, while cytochrome oxydase activity was increased by 25%. All measurements were made with a membrane preparation from strain AB1133. Notably, superoxide dismutase (SOD) reverted lactate dehydrogenase inhibition and growth inhibition of PA232 (pGC01) induced by MccJ25. Furthermore, we found a 25% increase in superoxide production by PA232 (pGC01) in the presence of MccJ25. We conclude that in E. coli AB1133 an increment of superoxide production could also be responsible for MccJ25 antibiotic activity, together with the already known  RNAP inhibition.