Part:BBa_K1666006

lsr promoter of LuxS/AI-2 signaling pathway in Salmonalla

Quorum sensing is a process of bacterial cell-to-cell communication involving the production and detection of extracellular signaling molecules called autoinducers. And autoinducer-2 (AI-2) has been proposed to serve as a 'universal signal' for interspecies communication. In the LuxS/AI-2 signaling system of Salmonella Typhimurium, AI-2 response involves ATP binding cassette transporter encoded by genes named Lsr (LuxS regulated). Plsr is the promoter of the lsr operon. In our project, we use it to trigger the expression of a reporter gene.

Usage and Biology

AI-2 is generated by many species of Gram-negative and Gram-positive bacteria. In a group of bacteria exemplified by Salmonella, AI-2 response involves lsr genes that encode ATP binding cassette-type transporter. Plsr is the promoter of the lsr operon.

Fig1. Schematic overview of the AI-2 response pathway in Salmonella TyphimuriumThe precursor of AI-2, 4,5-Dihydroxy-2,3-Pentanedione (DPD) , is a byproduct generated when LuxS converts S-Ribosylhomocysteine (SRH) to Homocysteine (HCY). DPD then undergoes spontaneously cyclization, forming AI-2, and exports to the culture supernatant. After that, extracellular AI-2 bounds to LsrB, following by passing the membrane channel and importing the cytoplasm. LsrK phosphorylates AI-2 afterwards. The lsr operon is repressed until phosphorylated AI-2 causes LsrR to relieve its repression on the promoter. And this allows further AI-2 import.

Plsr is an inducible promoter under the repressive regulation of LsrR. In our project, we use it to regulate the expression of the reporter gene, amilCP (BBa_K592009).When pathogenic bacteria express AI-2 molecules and secrete them extracellularly, these AI-2 molecules can be transported into our engineered bacteria and trigger the expression of the report gene to produce the blue pigment.

Fig2. Part of the vector containing Plsr

Characterization

We isolated the promoter region of the lsr operon to regulate the expression of the report gene, amilCP (BBa_K592009). In order to test the function of the plsr promoter, we transformed the plasmid pHY300PLK containing Plsr with a blue pigment gene at its downstream into E. coli Trans T1 primarily. As we can see, after overnight incubation, we observed blue colonies on the plate. That means without LsrR-mediated repression, the Plsr promoter will be constitutively active and promote the production of visible blue pigment.

Fig3. Engineered E. coli Trans T1 contains pHY300PLK-Plsr-amilCP

After we have successfully integrated pNZ9530 and the expression vectors for lsrB, R and K into the Lactobacillus genome, we sequentially transformed the Plsr-amilCP vector. We cultured our engineered Lactobacillus in the medium containing AI-2 secreted by E. coli CD-2. We used DH5alpha bacteria as a control because they do not produce any AI-2. Our engineered Lactobacillus showed clear blue color compared to the control. This suggested the Plsr promoter can indeed work as expected.

Fig4. Yogurt guarder incubated with culture supernatant of different bacteria

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]