PpoR is a conserved unpaired LuxR solo of Pseudomonas putida which binds N-acyl homoserine lactones.
BACKGROUND
Only a small number of Pseudomonas putida strains possess the typical N-acyl homoserine lactone quorum sensing system (AHL QS) that consists of a modular LuxR family protein and its cognate LuxI homolog that produces the AHL signal. Moreover, AHL QS systems in P. putida strains are diverse in the type of AHLs they produce and the phenotypes that they regulate.


RESULTS
We identified an unpaired LuxR solo (QS luxR homolog that occurs without the corresponding luxI homolog), which is highly conserved in both the AHL producing and non-AHL producing P. putida strains that we analyzed. In this study we report the cloning and functional characterization of this unpaired LuxR homolog designated PpoR. An AHL binding assay showed that PpoR protein binds to 3-oxo-C6-HSL. Studies using a ppoR promoter-lacZ reporter fusion revealed that it exhibits stringent growth phase dependent expression. Functional interaction of PpoR with the endogenous complete AHL QS systems of P. putida WCS358 (PpuI/R system) and PpoR was also investigated. Microarray analysis of P. putida WCS358 wild type and a PpoR over-expressing strain revealed several putative target genes that may be directly or indirectly regulated by PpoR.


CONCLUSIONS
Our results indicate that PpoR in P. putida strains may have a conserved role in detecting an AHL signal, either self or foreign, and regulating specific target genes.
Subramoni
Sujatha
S
Bacteriology Group, International Centre for Genetic Engineering & Biotechnology, Trieste, Italy. subramoni@icgeb.org
Venturi
Vittorio
V
D054742:Acyl-Butyrolactones / Q000378:metabolism*; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D017124:Conserved Sequence; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009154:Mutation; D016958:Pseudomonas putida / Q000235:genetics* / Q000378:metabolism; D053038:Quorum Sensing / Q000235:genetics; D012329:RNA, Bacterial / Q000235:genetics; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*
D054742:Acyl-Butyrolactones; D001426:Bacterial Proteins; D012329:RNA, Bacterial; D012097:Repressor Proteins; D015534:Trans-Activators; C064778:LuxR autoinducer binding proteins