POSTERS - BLAST X - University of Utah

BLAST X Poster #18
CYTOCHROME d BUT NOT CYTOCHROME o RESCUES THE TOLUIDINE BLUE GROWTH
SENSITIVITY OF arc MUTANTS IN E. COLI
Adrián F. Alvarez, Roxana Malpica, Martha Contreras, Edgardo Escamilla, Everardo Ramírez
and Dimitris Georgellis.
Departamento de Genética Molecular, Instituto de Fisiología Celular, Universidad Nacional
Autónoma de México, 04510 México D.F., México
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. Under anaerobic conditions, the ArcB sensor
kinase autophosphorylates and then transphosphorylates ArcA, which in this form acts as a
global transcriptional regulator that controls the expression of many operons involved in
respiratory or fermentative metabolism. Under aerobic conditions, the system is inactivated
through the inhibition of the kinase activity of ArcB by the quinone electron carriers, and the
subsequent ArcA dephosphorylation. 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. Toluidine blue is a
redox dye that, in presence of light, allows the production of reactive oxygen species (ROS). 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, seventeen 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. Finally, 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.
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