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J. Bacteriol. doi:10.1128/JB.00206-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Microcin J25 has a dual and independent mechanism of action in Escherichia Coli: RNA polymerase inhibition and increased superoxide production

Departamento de Bioquímica de la Nutrición, Instituto Superior de Investigaciones Biológicas (Consejo Nacional de Investigaciones Científicas y Técnicas - Universidad Nacional de Tucumán), and Instituto de Química Biológica "Dr. Bernabé Bloj", 4000 San Miguel de Tucumán, Argentina

^* To whom correspondence should be addressed. Email: rdmorero{at}fbqf.unt.edu.ar.

	Abstract

Microcin J25 (MccJ25) uptake by E. coli requires the outer-membrane receptor, FhuA, and the inner-membrane proteins TonB, ExbD, ExbB, and SbmA. MccJ25 appears to have two intracellular targets: (1) RNA polymerase (RNAP), which was described in Escherichia coli and Salmonella enterica serovars, and (2) respiratory chain, reported only in Salmonella enterica serovars. In the current study it is shown that the observed difference in the action of microcin on the respiratory chain between E. coli and S. enterica is due to the relatively low microcin uptake via the chromosomally encoded FhuA. Higher expression by a plasmid encoded FhuA allowed higher uptake of MccJ25 by E. coli strains and the consequent inhibition of the oxygen consumption. Both mechanisms, the inhibition of RNAP and oxygen consumption, are independent from each other. Further analysis revealed for the first time that MccJ25 stimulates the production of reactive oxygen species (O2^·-) in bacterial cells, which could be the main reason for the damage produced on the membrane respiratory chain.

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