Difference between revisions of "Part:BBa K3332038"

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pTrc-2

A promoter derived from pTrc-2 promoter can be strongly repressed by LacI protein. pTrc-2 promoter has one lac operator, which means that LacI has a weak inhibitory effect on it.

Usage and Biology

pTrc-2 promoter is used to express mf-lon and MazF in the absence of aTc so as to inhibit the growth of E.coli. It is part of the circut designed to prevent engineered bacteria in the detection instrument from escaping. In this circuit, LacI can repress pTrc-2 promoter and pTrc-2 derivative promoter，while tetR can repress pLtetO-1 promoter. When ATc exits, it can combine tetR, so that pLtetO-1 promoter can’t be repressed. Then LacI which is controlled by pLtetO-1 can repress pTrc-2 promoter and pTrc-2 derivative promoter. As a result, mf-lon and MazF can’t be expressed. As a kind of bacterial toxin, MazF can cause the bacteria death. So there comes the conclusion that as long as the engineered E.coli are cultured in the environment with ATc, it won’t be killed by MazF, but when the E.coli escape from our testing instrument, the effect can be reversed, that is to say, the E.coli will be killed by MazF. In the same way, we can conclude that in the presence of IPTG, MazF can be expressed to cause bacterial death.

Fig.1 Circuit.

Characterization

The agarose gel electrophoresis images are below:

Fig.2 pTrc-2_E0420_pSB1C3[BBa_K3332086] digested by Xba I and Pst I.(about 1003 bp)

Fig.3 pTrc-2 derivative_E0420_pUC57[BBa_K3332087] digested by EcoR I and Pst I. (about 1018 bp)

Fig.4 pLtetO-1_RBS1_lacI_B0015_pTrc-2_E0420_pUC57[BBa_K3332088] digested by Pst I (about 5086 bp).

Fig.5 pLtetO-1_RBS1_lacI_B0015_pTrc-2 derivative_E0420_pUC57[BBa_K3332089] digested by Pst I (about 5125 bp). note: E0420 is equal to B0034_E0020_B0015

Protocol

1. Preparation of stock solution:dissolve IPTG in absolute alcohol to make 1000× stock solution

2.Culture glycerol bacteria containing the corresponding plasmid in test tube for 12h.

3.Add 4ml of the above bacterial solution into 100 mL LB medium and maintain the culture condition at 37 ℃ and 180 rpm.

4.Add 100μL IPTG stock solution into the induction group when OD increased to 0.6.

5.Induce for 6 hours and the condition is the same as before.

6.Then, sampling 0.5ml culture in each tube. All samples are centrifuged at 12000rpm, 1 minute. Remove supernatant and add 500µl sterile PBS to resuspend.

7.Measure the fluorescence intensity(ECFP)and corresponding OD600 by 96-well plate reader, then calculate the fluorescence / OD value of each group. Here is the result:

Fig.6 Fluorescence intensity/OD600 for induction and non-induction group (6 hours). Data are collected and analyzed according to iGEM standard data analysis form after 6 hours of induction.

The strength of pTrc2-derivative and pTrc2 are contrasted. In the figure, pTrc2-derivative are used as the negative control group, pTrc2-derivative-E0420(ECFP) are used as the positive control group while pLtetO-1-LacI-pTrc2-E0420 (ECFP) and pLtetO-1-LacI-pTrc2-derivative-E0420(ECFP) are both experimental group. We can see, after adding IPTG to induce the two promoters, the fluorescence intensity are both improved. The change of fluorescence intensity after induction of pLtetO-1-LacI-pTrc2-E0420(ECFP) group is larger than the pLtetO-1-LacI-pTrc2-derivative-E0420(ECFP) group, so we can confirm that the LacI has a weak inhibitory effect on pTrc-2 promoter and a strong inhibitory effect on pTrc-2 derivative promoter.

Fig.7 In each group，the EP tube on the left is without induction while the one on the right is with induction.

From this figure, the induction effect can be seen more intuitively.

Sequence and Features

Reference

[1] Chan CT, Lee JW, Cameron DE, Bashor CJ, Collins JJ. 'Deadman' and 'Passcode' microbial kill switches for bacterial containment. Nat Chem Biol. 2016;12(2):82-86. doi:10.1038/nchembio.1979