title: The branched CcsA/CckA-ChpT-CtrA phosphorelay of Sphingomonas melonis controls motility and biofilm formation.
abstract: The CckA-ChpT-CtrA phosphorelay is central to the regulation of the cell cycle in Caulobacter crescentus. The three proteins are conserved in Alphaproteobacteria, but little is known about their roles in most members of this class. Here, we characterized the system in Sphingomonas melonis. We found that the transcription factor CtrA is the master regulator of flagella synthesis genes, the hierarchical transcriptional organization of which is herein described. CtrA also regulates genes involved in exopolysaccharide synthesis and cyclic-di-GMP signaling, and is important for biofilm formation. In addition, the ctrA mutant exhibits an aberrant morphology, suggesting a role for CtrA in cell division. An analysis of the regulation of CtrA indicates that the phosphorelay composed of CckA and ChpT is conserved and that the absence of the bifunctional kinase/phosphatase CckA apparently results in overactivation of CtrA through ChpT. Suppressors of this phenotype identified the hybrid histidine kinase CcsA. Phosphorelays initiated by CckA or CcsA were reconstituted in vitro, suggesting that in S. melonis, CtrA phosphorylation is controlled by a branched pathway upstream of ChpT. This study thus suggests that signals can directly converge at the level of ChpT phosphorylation through multiple hybrid kinases to coordinate a number of important physiological processes.
authors.affiliation: Institute of Microbiology, ETH Zurich, 8093, Zurich, Switzerland.
authors.forename: Anne
authors.initials: A
authors.lastname: Francez-Charlot
authors.affiliation: Institute of Microbiology, ETH Zurich, 8093, Zurich, Switzerland.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kaczmarczyk
authors.affiliation: Institute of Microbiology, ETH Zurich, 8093, Zurich, Switzerland.
authors.forename: Julia A
authors.initials: JA
authors.lastname: Vorholt
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D018441:Biofilms / Q000254:growth & development*; D002453:Cell Cycle / Q000235:genetics; D002455:Cell Division; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D005407:Flagella / Q000235:genetics* / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D000071677:Histidine Kinase; D009154:Mutation; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D015398:Signal Transduction; D020578:Sphingomonas / Q000235:genetics* / Q000502:physiology*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C097706:CtrA protein, Caulobacter; D004268:DNA-Binding Proteins; D014157:Transcription Factors; C062025:bis(3',5')-cyclic diguanylic acid; D011494:Protein Kinases; D000071677:Histidine Kinase; D006152:Cyclic GMP