Part:BBa_K1632012:Experience
PBAD/araC_rbs_fimB(wild-type)
Contents
Materials and Methods
Construction
All the samples were DH5alpha strain with antibiotic resistance to ampicillin and kanamycin.
A. PBAD/araC_fimB(wild-type) (pSB6A1) + fim switch[default ON](wild-type)_rbs_gfp (pSB3K3)
B. PBAD/araC_fimB(wild-type) (pSB6A1) + fim switch[default OFF](wild-type)_rbs_gfp (pSB3K3)
C. pSB6A1 + fim switch[default ON](wild-type)_rbs_gfp (pSB3K3) …positive control 1
D. pSB6A1 + fim switch[default OFF](wild-type)_rbs_gfp (pSB3K3) …negative control 1
E. PBAD/araC_fimB(wild-type) (pSB6A1) + J23119_rbs_gfp(pSB3K3) …positive control 2
F. PBAD/araC_fimB(wild-type) (pSB6A1) + rbs_gfp(pSB3K3) …negative control 2
Flow cytometer
Assay protocol
1. Prepare overnight cultures for each sample in 3 mL of LB medium containing ampicillin (50 microg / mL), kanamycin (30 microg / mL) and glucose (final concentration is 0.5 %) at 37 ℃ for 12h.
2. Make a 1:100 dilution in 3 mL of fresh LB containing Amp, Kan and glucose (final concentration is 0.5 %).
3. Incubate the cells at 37 ℃, shaking at 180 rpm until the observed OD590 reaches 0.4 (Fresh Culture).
4. After the incubation, take 1 mL of the samples, and centrifuge at 5000x g, 1 min, 25 ℃
5. Remove the supernatant.
6. Suspend the pellet in 1 mL of LB containing Amp and Kan, and centrifuge at 5000x g, 1 min, 25 ℃
7. Remove the supernatant.
8. Suspend the pellet in 1 mL of LB containing Amp and Kan, and centrifuge at 5000x g, 1 min, 25 ℃
9. Remove the supernatant.
10. Suspend the pellet in 1 mL of LB containing Amp and Kan.
11. Add 30 microL of suspension in the following medium.
① 3 mL of LB containing Amp, Kan, glucose (final concentration is 0.5 %) and 30 microL of sterile water
② 3 mL of LB containing Amp, Kan and 30 microL of 2 mM arabinose (final concentration of arabinose is 20 microM)
③ 3 mL of LB containing Amp, Kan and 30 microL of 20 mM arabinose (final concentration of arabinose is 200 microM)
④ 3 mL of LB containing Amp, Kan and 30 microL of 500 mM arabinose (final concentration of arabinose is 5 mM)
※ As for (3) and (4), the suspension were added only in medium ① and ④.
12. Incubate the samples at 37 ℃, shaking at 180 rpm for 6.5 hours. (Measure OD590 of all the samples every hour.)
13. After the incubation, take the samples, and centrifuge at 9000x g, 1min, 4℃.
14. Remove the supernatant.
15. Add 1 mL of filtered PBS (phosphate-buffered saline) and suspend. (The ideal of OD is 0.3)
16. Dispense all of each suspension into a disposable tube through a cell strainer.
17. Use flow cytometer to measure the fluorescence of GFP. (We used BD FACSCaliburTM Flow Cytometer of Becton, Dickenson and Company.)
Results
Discussion
We tried to confirm that fim switch is bidirectically inverted in the presence of FimB(wild-type) by using GFP as a reporter, under 4 different concentrations of arabinose. In the medium with 0 M arabinose, we supplemented the medium with 0.5 % glucose in order to repress the leakage in the PBAD/araC promoter. Fig. 2 shows the histograms of the samples measured by the flow cytometer. In the results of the reporter cell (1), when the Induction of FimB(wild-type) expression increases, the fluorescence intensity decreases. From this fact, we confirmed that the fim switch is inverted from [ON] state to [OFF] state by FimB(wild-type). From the result of the reporter cell (2), when the expression amount of FimB(wild-type) increases, the expression amount of GFP in the reporter cell (2) increases. From this fact, we confirmed that the fim switch is inverted from [OFF] state to [ON] state by FimB(wild-type). From the results of the two reporter cells (1) and (2), we successfully confirmed that FimB(wild-type) inverts the fim switch from [ON] state to [OFF] state and from [OFF] state to [ON] state.
When the concentration of FimB(wild-type) increased by increasing concentration of arabinose, we confirmed that the fluorescence intensity decreased in both [ON] to [OFF] process and [OFF] to [ON] process.
The result of the reporter cell (2) shows that when the concentration of arabinose is increased to 0〜20 microM, the fluorescence intensity increases. This shows the function of FimB(wild-type) inverting the fim switch(wild-type) from [OFF] state to [ON] state. However, when the arabinose concentration is excess amount (5mM), the fluorescence intensity decreases (Fig. 3). According to [1], this is caused by the excess increase of the inversion rate of the fim switch. When the inversion rate is too high, there is not enough time for transcription initiation. Consequently, the GFP expression decreases.
Supplemental experience
Assay protocol
1. After the assay of “Arabinose dependent FimE expression”, miniprep cell culture ((1)-①, (1)-③, (2)-① and (2)-③) of leftover as here.(https://parts.igem.org/Help:Protocols/Miniprep)
2. Turn on water bath to 42℃.
3. Take competent DH5alpha strain from -80℃ freezer and leave at rest on ice.
4. Add 3 µl of each plasmids in a 1.5 ml tube.
5. Put 25 µl competent cell into each 1.5 ml tubes with plasmid.
6. Incubate on ice for 15 min.
7. Put tubes with DNA and competent cells into water bath at 42℃ for 30 seconds.
8. Put tubes back on ice for 2 minutes.
9. Add 125 µl of SOC medium. Incubate tubes for 30 minutes at 37℃.
10. Make a 1:5 dilution in 150 µl of fresh SOC medium.
11. Spread about 100 µl of the resulting culture of LB plate containing kanamycin.
12. Incubate LB plate for 14-15 hours at 37℃.
13. Set the plate reader to measure GFP.
14. Scan the each plates with the plate reader. (We used FujiFilm FLA-5100 Fluorescent Image Analyzer from FUJIFilm Life Science.)
15. Analyze the scanning data by changing the scale type (Bezier) and adjusting the range. (We analyzed by using the software, Multi Gauge ver. 2.0 from FUJIFilm Life Science.)
16. Counted out the all colonies and those with fluorescence.
17. Prepare three overnight cultures for each sample in 3 mL of LB medium containing kanamycin (30 microg / mL) shaking at 180 rpm for 12h.
18. Miniprep each samples and ask DNA sequencing of each samples for Biomaterial Analysis Center, Technical Department.
Results
Discussion
To confirm our results that our FimB(wild-type) inverted the fim switch(wild-type) further, after scattering the samples on a plate, we counted the number of colonies which were expressing GFP and the colonies which were not expressing GFP(Fig.4). The state of fim switch either [ON] or [OFF] in colonies is evaluated from fluorescence. In brief, colonies which contain fim switch[default ON] expresse GFP while colonies which contain fim switch[default OFF] do not express GFP. We counted out the all colonies and colonies which contain fim switch[default ON]. In the results of the reporter cell (1), when the expression of FimB(wild-type) was induced by arabinose, the percentage of [ON] state decreased. Furthermore, from the results of the reporter cell (2), when the expression of FimB(wild-type) was induced, the percentage of [ON] state increased. From the results of the two reporter cells (1) and (2), we successfully confirmed that the fimB protein inverts the fim switch(wild-type) from [ON] state to [OFF] state and from [OFF] state to [ON] state. (Fig.4). This result was consistent with the histograms (Fig. 2)
Also, we incubated the colonies with fluorescence and the colonies without fluorescence. We minipreped cell cultures. Sequence complementarity of the each sample in the specific region of the switch shows intended inversion of the switch from [ON] state to [OFF] state in all samples (Fig. 5.).
More information
For more information, see http://2015.igem.org/Team:Tokyo_Tech/Project Our work in Tokyo_Tech 2015 wiki, http://2015.igem.org/Team:Tokyo_Tech/Experiment/ssrA_tag_degradation_assay About ssrA-tag, http://2015.igem.org/Team:Tokyo_Tech/Experiment/Overview_of_fim_inversion_system About ''fim'' inversion system