JB Accepts, published online ahead of print on 6 November 2009
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J. Bacteriol. doi:10.1128/JB.00881-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Cytochrome d but not cytochrome o rescues the toluidine blue growth sensitivity of arc mutants in Escherichia coli

Adrian F. Alvarez, Roxana Malpica, Martha Contreras, Edgardo Escamilla, and Dimitris Georgellis

Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, 04510 México D.F., México


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Abstract

The Arc (anoxic redox control) two-component signal transduction system, consisting of the ArcB sensor kinase and the ArcA response regulator, allows adaptive responses of Escherichia coli to changes of O2 availability. The arcA gene was previously known as the dye gene because null mutants were growth sensitive to the photosensitizer redox dyes toluidine blue and methylene blue, a phenotype whose molecular basis still remains elusive. In this study we report that the toluidine blue O effect on the arc mutants is light independent, and only observed during aerobic growth conditions. Moreover, sixteen suppressor mutants with restored growth were generated and analyzed. Thirteen of those possessed insertion elements (IS) upstream the cydAB operon, rendering its expression ArcA independent. Also, it was found that, in contrast to cythocrome d, cythocrome o was not able to confer toluidine blue resistance to arc mutants, thereby representing an intriguing difference between the two terminal oxidases. Finally, a mechanism for toluidine blue O sensitivity and resistance is discussed.






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