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Summary   Aggregatibacter actinomycetemcomitans  Qse BC  regulates its own expression and is essential for biofilm growth and virulence. However, the signal that activates the QseC sensor has not been identified and the qse BC  regulon has not been defined. In this study, we show that QseC is activated by catecholamine hormones and iron but not by either component alone. Activation of QseC requires an  EYRDD  motif in the periplasmic domain of the sensor and site‐specific mutations in  EYRDD  or the deletion of the periplasmic domain inhibits catecholamine/iron‐dependent induction of the  ygiW‐qse BC   operon. Catecholamine/iron‐dependent induction of transcription also requires interaction of the QseB response regulator with its binding site in the  ygiW‐qse BC   promoter. Whole genome microarrays were used to compare gene expression profiles of  A. actinomycetemcomitans  grown in a chemically defined medium with and without catecholamine and iron supplementation. Approximately 11.5% of the  A. actinomycetemcomitans  genome was differentially expressed by at least two‐fold upon exposure to catecholamines and iron. The expression of ferritin was strongly induced, suggesting that intracellular iron storage capacity is increased upon Qse BC  activation. Consistent with this, genes encoding iron binding and transport proteins were down‐regulated by Qse BC . Strikingly, 57% of the Qse BC  up‐regulated genes (56/99) encode proteins associated with anaerobic metabolism and respiration. Most of these up‐regulated genes were recently reported to be induced during  in vivo  growth of  A. actinomycetemcomitans . These results suggest that detection of catecholamines and iron by Qse BC  may alter the cellular metabolism of  A. actinomycetemcomitans  for increased fitness and growth in an anaerobic host environment.

molecular oral microbiology

Aggregatibacter actinomycetemcomitans  Qse BC  is activated by catecholamines and iron and regulates genes encoding proteins associated with anaerobic respiration and metabolism