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Microcin J25 Has Dual and Independent Mechanisms of Action in Escherichia coli: RNA Polymerase Inhibition and Increased Superoxide Production

Augusto Bellomio, Paula A. Vincent, Beatriz F. de Arcuri, Ricardo N. Farías, and Roberto D. Morero^*

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

Received 7 February 2007/ Accepted 18 March 2007

Microcin J25 (MccJ25) uptake by Escherichia coli requires the outer membrane receptor FhuA and the inner membrane proteins TonB, ExbD, ExbB, and SbmA. MccJ25 appears to have two intracellular targets: (i) RNA polymerase (RNAP), which has been described in E. coli and Salmonella enterica serovars, and (ii) the respiratory chain, reported only in S. enterica serovars. In the current study, it is shown that the observed difference between the actions of microcin on the respiratory chain in 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 greater uptake of MccJ25 by E. coli strains and the consequent inhibition of oxygen consumption. The two mechanisms, inhibition of RNAP and oxygen consumption, are independent of 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.

Published ahead of print on 30 March 2007.

A. Bellomio and P. A. Vincent contributed equally to this work.

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