LLDPRD can sense the presence of lactic acid, in the absence of lactic acid, only a lower background level of expression, but in the presence of lactic acid can open expression and gene transcription.
LuxS gene can produce LuxS protein and catalyze the formation of AI-2., a signaling molecule of the quorum sensing pathway. When the promoter of LuxS gene is replaced by LLDPRD operon promoter, the LuxS gene will be activated in the presence of lactic acid, thus the quorum-sensing can be started.
LLDPRD can sense the presence of lactic acid, in the absence of lactic acid, only a lower background level of expression, but in the presence of lactic acid can open expression and gene transcription.
LLDR can inhibit or activate lldPRD. We believe that the binding of LLDR to lldPRD operon promoter under the condition of lactic acid deficiency may lead to DNA translation and transcriptional inhibition. The binding of L- lactic acid to LLDR can promote conformation change, thus destroy the DNA cycle and form a transcriptional open complex. At the same time, the LuxS gene can be regulated to activate the quorum sensing system of Escherichia coli, through which the lactic acid sensor can be combined with the quorum sensing.
The aim of this part is using llDPRD promoter to activate downstream GFP reporter gene expression under different lactic acid concentration inductions and this operon is repressed without lactic acid induction. Briefly, LLdR repression protein specifically binds to llDPRD promoter and impedes downstream gene expression, while lactic acid enables to antagonize and replace LLdR protein to activate llDPRD promoter.
This part is designed to detect whether the LsrA promoter activation is controlled by the quorum sensing signal via monitoring the GFP reporter gene expression.
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