Part:BBa_K1139201:Experience
PphoA-GFP-TT
Contents
Materials and Methods
1. Construction
-pSB6A1-Ptet-GFP (MG1655)… positive control
-pSB6A1-ΔP-GFP (MG1655)… negative control
-pSB6A1-PphoA-GFP (MG1655)…BBa_K1139201
The phoA promoter region of E. coli was amplified from MG1655 genomic DNA by PCR using upstream primer (5’-acgtgaattcgcggccgcttctagagaaagttaatcttttcaacagctgtcataaag-3’) and downstream primer (5’-ccgctactagtaaatacattaaaaaataaaaacaaagcgactataagtctc-3’). Amplification was carried out with the steps shown in Fig. 1.
2. Assay Protocol
- 2-0. Prepare MOPS minimal medium as follows (F. Neidhardt et al., 1974).
Also, prepare a series of phosphate concentration gradient 1X MOPS by changing the volume of K2HPO4 (We prepared the series as 0, 10, 30, 100, 300, 1000 µM).
[ Prepare MOPS minimal medium ]
200 mL of 1X MOPS is prepared as follows.
Component | Volume |
10X MOPS mixture | 20 mL |
0.132 M K2HPO4 | 2 mL |
milliQ H2O | 176 mL |
TOTAL | 200 mL |
1. Mix ingredients above and adjust the pH to 7.2 with 5 M NaOH.
2. Filter sterilize. It can be stored at 4°C, for up to 1 month.
3. Before use, add carbon source (we used a final concentration of 0.1% glucose).
[ 10X MOPS mixture (200 mL) ]
1. Add the following to ~60 mL milliQ H2O:
Component | Grams |
MOPS | 16.7 |
Tricine | 1.43 |
2. Add 5 M KOH to a final pH of 7.4
3. Bring total volume to 88 mL
4. Make fresh FeSO4 solution and add it to the MOPS/Tricine solution:
Component | Volume |
0.01 M FeSO4•7H2O | 2 mL |
5. Add the following solutions to the MOPS/Tricine/FeSO4 solution
(Mix in the order shown)
Component | Volume |
1.9 M NH4Cl | 10 mL |
0.276 M K2SO4 | 2 mL |
0.02 M CaCl2•H2O | 0.05 mL |
2.5 M MgCl2 | 0.42 mL |
5 M NaCl | 20 mL |
Micronutrient stock | 0.04 mL |
Autoclaved milliQ H2O | 77.4 mL |
TOTAL | 200 mL |
6. Filter sterilize with 0.2 micron filter
7. Aliquot into sterile plastic bottle and freeze at -20°C.
[ Micronutrient stock (50 mL) ]
Mix everything together in 40 mL autoclaved milliQ H2O, bring up total volume to 50 mL.
Store at room temperature.
Component | Formula | Grams for 50 mL |
ammonium molybdate | (NH4)6Mo7O24•4H2O | 0.009 |
boric acid | H3BO3 | 0.062 |
cobalt chloride | CoCl2 | 0.018 |
cupric sulfate | CuSO4 | 0.006 |
manganese chloride | MnCl2 | 0.040 |
zinc sulfate | ZnSO4 | 0.007 |
- 2-1. Prepare overnight culture of BBa_K1139201, positive control and negative control, each in MOPS medium (including 1.32 mM K2HPO4) containing ampicillin (50 µg/mL) at 37°C.
- 2-2. Dilute the overnight cultures to an OD600 of 0.1 in fresh MOPS medium (3 mL) containing ampicillin (50 µg/mL). (→fresh cultures)
- 2-3. Incubate the fresh cultures until the observed OD600 reaches 0.4-0.6.
- 2-4. Centrifuge the cells at 6,000g, 25°C, 10 minutes, wash twice with MOPS minimal medium without phosphate containing ampicillin (50 µg/mL), and then suspend in the same medium to obtain a final OD600 of 10.
- 2-5. Add 300 µL of prepared cell suspension to 2.7 mL of test solution, the series of phosphate concentration gradient 1X MOPS, containing ampicillin (50 µg/mL)
- 2-6. Incubate the cells for 140 minutes at 26°C.
- 2-7. 1 mL of each culture was harvested by centrifugation and suspended by adding 1 mL of PBS (phosphate-buffered saline). Dilute the suspension to obtain a final OD600 of around 0.2 by PBS.
- 2-8. Dispense 600 µL of each suspension into a disposable tube through a cell strainer. Fluorescence intensity was measured with a flow cytometer of Becton, Dickinson and Company.
Results
1. Before inducing by phosphate concentration
Fig. 2.1 shows the fluorescence intensity of the fresh cultures (the MOPS medium which contains 1.32 mM K2HPO4) incubated until the observed OD600 reached 0.4-0.6 (Assay protocol 1-2-3). phoA promoter was repressed because the MOPS medium contained 1.32 mM phosphate, which was a high concentration for phoA promoter.
2. After inducing by phosphate concentration
Fig. 2-1 shows the fluorescence intensity of the induced cells by phosphate concentration. Fig. 2-2 shows the picture of fluorescence of the induced cells. The increase in phosphate concentration repressed the phoA promoter. Especially, we saw that the phoA promoter was drastically repressed at phosphate concentrations of 100 to 300 µM.
Discussion
We confirmed that the increase in phosphate concentration repressed the phoA promoter. Compared to OUC-China’s phosphate sensor part (BBa_K737024) including phoB promoter (Fig. 3-2), our phosphate sensor part shows clearer result.
Moreover, plants are reported to be in phosphate starvation under the concentration of 1 mM (D. Hoagland et al., 1950). Our part can also sense the concentration below 1 mM. Therefore, this part will lead us to our goal to create E. coli which could increase plant growth by synthesizing several plant hormones depending on the soil environment.
For more information, see [http://2013.igem.org/Team:Tokyo_Tech/Experiment/phoA_Promoter_Assay our work in Tokyo_Tech 2013 wiki].
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