A novel sensor kinase-response regulator hybrid regulates type III secretion and is required for virulence in Pseudomonas aeruginosa.
The type III secretion system (TTSS) of Pseudomonas aeruginosa is induced by contact with eukaryotic cells and by growth in low-calcium media. We have identified a protein, RtsM, that is necessary for expression of the TTSS genes in P. aeruginosa. RtsM possesses both histidine kinase and response regulator domains common to two-component signalling proteins, as well as a large predicted periplasmic domain and seven transmembrane domains. Deletion of rtsM resulted in a defect in production and secretion of the type III effectors. Northern blot analysis revealed that mRNAs encoding the effectors ExoT and ExoU are absent in the DeltartsM strain under TTSS-inducing conditions. Using transcriptional fusions, we demonstrated that RtsM is required for transcription of the operons encoding the TTSS effectors and apparatus in response to calcium limitation or to host cell contact. The operon encoding the TTSS regulator ExsA does not respond to calcium limitation, but the basal transcription rate of this operon was lower in deltartsM than in the wild-type parent, PA103. The defect in TTSS effector production and secretion of deltartsM could be complemented by overexpressing ExsA or Vfr, two transcriptional activators involved in TTSS regulation. DeltartsM was markedly less virulent than PA103 in a murine model of acute pneumonia, demonstrating that RtsM is required in vivo. We propose that RtsM is a sensor protein at the start of a signalling cascade that induces expression of the TTSS in response to environmental signals.
Laskowski
Michelle A
MA
Program in Microbiology, Yale University School of Medicine, P O Box 208022, New Haven, CT 06520-8022, USA.
Osborn
Ellice
E
Kazmierczak
Barbara I
BI
D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism; D005260:Female; D015964:Gene Expression Regulation, Bacterial; D000071677:Histidine Kinase; D051379:Mice; D008810:Mice, Inbred C57BL; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011552:Pseudomonas Infections; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000378:metabolism / Q000472:pathogenicity; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; C112177:osmolarity response regulator proteins; D011494:Protein Kinases; D000071677:Histidine Kinase; D002118:Calcium