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This is a promoter that is activated in an acidic environment.

This is a promoter that is activated in an acidic environment. It is the promoter of the acid shock protein ASP in E. coli, and its sequence contains a RstA box that can be bound by phosphorylated RstA to enhance its promoter activity in a dose-dependent manner[1]. The team obtained the corresponding promoter fragment from the E. coli MG1655 genome by PCR using a high-fidelity DNA polymerase. 

Usage

The promoter of the acid shock protein ASP in E.coli often functions under acidic stress conditions. Since its sequence contains a series of binding sites for regulatory proteins such as the RstA box, its activity can be well artificially regulated and altered. Therefore, it can be well utilized in synthetic biology circuit design. Some experimental teams have combined pH sensing with toxin expression to create an effective bacterial containment system [2]. We believe the functionality of this promoter in responding to environmental pH changes could provide some reference meaning to projects detecting changes in environmental pH conditions. 

Test Method Design

Charaterization of Pasr promoter with fluorescence intensity measurement

To validate the obtained promoter activity and its activation range in response to pH, we connected Amcyan protein after this promoter and introduced it into E. coli BL21(DE3). When E. coli grew to OD600=0.6, we used HCl aqueous solution and NaOH aqueous solution to adjust the pH and built a gradient from pH 8 to pH 3. Fluorescence intensity (Exλ:453nm Emλ:486nm) was measured every 30 minutes for 5 hours while OD600 was measured simultaneously. The final fluorescence intensity divided by OD600 gave the relative fluorescence intensity. 

Test Protocol

    1) Methods of molecular cloning and transformation are described above. Transform this plasmid into E. coli BL21. Then spread it onto an LB medium plates with 50 μg/mL kanamycin and incubate overnight at 37 ℃ in an incubator.

    2) Pick four colonies from the same plate as parallel repeats. Each colony is inoculated on two identical media with 5mL LB medium containing 50 μg/mL kanamycin and cultured at temperatures(36 ℃) respectively while shaking at 200 rpm .

    3) Measure the OD₆₀₀ value of the resuspending culture media in an automatic microplate reader (SynergyH1 hybrid multimodal reader)until the OD₆₀₀ is in the range of 0.4 and 0.6.

    4) Use HCl aqueous solution and NaOH aqueous solution to adjust the pH of the medium, and construct a gradient from pH 8 to pH 3.

    5) Samples were grouped and incubated continuously at 37 ° C while shaking at 200 rpm for four hours.

    6) Fluorescence intensity (Ex.lamda.: 453 nm, Em.lamda.: 486 nm) and OD₆₀₀ were measured continuously using a an automatic microplate reader (Synergy H1 hybrid multimodal reader). At the end of the detection, the measured fluorescence intensity was divided by OD₆₀₀ to obtain the relative fluorescence intensity, and the results were analyzed by plotting.

Result

Analysis of the experimental results

As shown in Figure 1., Pasr has almost no expression under pH 7-8 conditions, but begins low-dose expression at pH 6 and gradually increases as the pH decreases, reaching a peak at pH = 5, then maintaining a relatively low expression level as the pH continues to decline. As shown in Figure 2.,We selected the final values for differential analysis, which showed extremely significant differences between pH 6, pH 5 and the control group. This experiment validated that this promoter has almost no expression under pH 7-8 conditions, consistent with our project design expectations. Pasr can be used to activate the suicide circuit in the gastric environment of cats to cause engineered bacteria death, thus avoiding potential hazards from leakage. This promoter can be used to respond to changes in environmental pH and has some reference value for projects with corresponding environmental condition changes.

Reference

[1]Ogasawara H, Hasegawa A, Kanda E, Miki T, Yamamoto K, Ishihama A. Genomic SELEX search for target promoters under the control of the PhoQP-RstBA signal relay cascade. J Bacteriol. 2007 Jul;189(13):4791-9.

[2] Stirling F, Naydich A, Bramante J, Barocio R, Certo M, Wellington H, Redfield E, O'Keefe S, Gao S, Cusolito A, Way J, Silver P. Synthetic Cassettes for pH-Mediated Sensing, Counting, and Containment. Cell Rep. 2020 Mar 3;30(9):3139-3148.e4.

Sequence and Features