pLsr + RBS + sfGFP
The Lsr quorum sensing pathway is a non-species specific cell-to-cell communication pathway used by both Gram-positive and Gram-negative bacteria and is found in at least 55 strains of them, most notably strains of E. coli, S. typhimurium, and V. harveyi . Production of the chemical messenger AI-2 is mediated by the enzymes Pfs and LuxS, which metabolizes the toxic metabolic product S-adenosylhomocysteine (SAH) in a stepwise manner to form AI-2 .
The transporter protein cluster LsrACDB (depicted as the gray channel through which AI-2 passes to enter the host cell) facilitates the uptake of AI-2 . LsrR represses the pLsr promoter, which endogeneously is upstream of the lsrACDBFG and lsrRK operons, but in the context of synthetic biology can be placed upstream of any coding sequence of interest. LsrK phosphorylates and hence activates AI-2, allowing it to bind to LsrR and relieve its repression on pLsr, thus inducing the expression of the gene downstream of pLsr via an indirect mechanism .
Quorum sensing coordinates key cooperative behaviours in bacteria, including the formation of biofilms . As we are interested in urinary tract infections involving biofilms, we linked an existing GFP part downstream of this pLsr promoter which is also an existing part in the Registry to test the promoter's function and gather some preliminary data to help us explore the possibility of integrating a quorum sensing element into our antibiofilm/antibacterial secretion design to create a pathogen-responsive autonomous setup.
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