Abstract
Autoinducer-2 (AI-2) is a quorum sensing signal that mediates communication within and between many bacterial species. However, its known receptors (LuxP and LsrB families) are not found in all the bacteria capable of responding to this signaling molecule. Here, we identify a third type of AI-2 receptor, consisting of a dCACHE domain. AI-2 binds to the dCACHE domain of chemoreceptors PctA and TlpQ of Pseudomonas aeruginosa, thus inducing chemotaxis and biofilm formation. Boron-free AI-2 is the preferred ligand for PctA and TlpQ. AI-2 also binds to the dCACHE domains of histidine kinase KinD from Bacillus subtilis and diguanylate cyclase rpHK1S-Z16 from Rhodopseudomonas palustris, enhancing their enzymatic activities. dCACHE domains (especially those belonging to a subfamily that includes the AI-2 receptors identified in the present work) are present in a large number of bacterial and archaeal proteins. Our results support the idea that AI-2 serves as a widely used signaling molecule in the coordination of cell behavior among prokaryotic species.
Highlights
Autoinducer-2 (AI-2) is a quorum sensing signal that mediates communication within and between many bacterial species
We found that AI-2 is recognized by double CAlcium channels and CHEmotaxis receptors (dCACHE) domains of the Bacillus subtilis histidine kinase (HK) KinD and the Rhodopseudomonas palustris diguanylate cyclase (DGC) rpHK1S-Z16, leading to the induction of their enzymatic activity
P. aeruginosa does not produce AI-2, it robustly responds to this signaling molecule produced by neighboring heterologous bacteria, leading to changes in the expression of many genes, including those involved in virulence and biofilm formation[16,17,18]
Summary
Autoinducer-2 (AI-2) is a quorum sensing signal that mediates communication within and between many bacterial species. Its known receptors (LuxP and LsrB families) are not found in all the bacteria capable of responding to this signaling molecule. Bacterial quorum sensing (QS) is a cell–cell communication process that is mediated by autoinducers and allows bacteria to coordinate their behaviors in a cell densitydependent manner[1,2]. Two AI-2 forms engaged by corresponding bacterial receptors have been identified, including the boron-containing DPD derivative S-2-methyl-. LuxP bound to AI-2 converts the activity of the transmembrane sensor histidine kinase (HK) LuxQ from kinase to phosphatase, regulating gene expression and changing many density-dependent phenotypes such as bioluminescence, biofilm formation and virulence factor production[1,4,8], whereas the LsrB-AI-2 complex engages the membrane components of the ATP-binding cassette transporter system Lsr to deliver AI-2 into a OOC
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