Team:Tokyo Tech

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Main Protcol Parts Submitted to the Registry Our Team Acknowledgements



Contents

1 Our project

Our project is creation of "Coli Touch"!!

What is "Coli touch"?

Coli Touch” has a pressure sensitive display composed of an E. coli lawn. When you touch its display, touched section is colored.
Next I'll tell you about “Coli Touch” work system. Display of “Coli Touch” has many E. coli. When you touch this display, pressure-input travels to E. coli in this display. And pressure applied E. coli expresses GFP.

Why pressure?

Coli Touch” uses pressure as input. Why we use pressure input? Past input ways (small molecule, heat and light) are difficult to induce uniformly. Pressure-input can induce uniformly.

2 Pressure induction

Introduction

 
A tet promoter is known as a sensitive one to pressure. (T. Sato et al., 1995)

Construction

figure2-1. We constructed Ptet-GFP and promoter less-GFP for confirmatory experiment

 
We chose tet promoter(Ptet) as pressure-inducible promoter. We constructed two plasmids - one is Ptet-GFP on pSB6. The other is promoter less-GFP on pSB6 as a negative control.We experimented under 0.1 MPa and 30 MPa pressure.

Result ~ activity of tet promoters ~

figure2-2. Pressure response of tet promoters. Tet promoters' activity increased under 30 MPa

 
The result shows that tet promoters activity under 30 MPa pressure is about 3 fold stronger than tet promoters activity under 0.1 MPa pressure. Therefore, we confirmed that tet promoters was induced under 30 MPa pressure.



          

          

          

          

          

          

          

          

          

          

          

3 Touch display

Touch display (plan)

figure 3-1-b. Design of touch display

 
Touch display that we planned has many holes, and E. coli is in these holes.(figure 3-1 a)
As the first step of creating the touch display,we created Prototype touch display. figure 3-1 b)

 

 

figure 3-1-a. Plan to create touch display. We created two-holes display as the first step.


Prototype touch display

figure 3-2. Prototype touch display. The display has two kinds of holes and two kinds of covers.

 

We created a Prototype touch display made of acrylic glasses. This touch display has two kinds of holes(show figure 3-2). Each hole contains culture medium and E. coli is cultivated in those holes. One hole (A) can be pressurized, because the hole is covered with only a plastic tape. And water pressure conducts into the hole. The other (B) is not pressurized, because the hole is covered with a block made of acrylic glasses. Water pressure doesn’t conduct into the hole.

 

figure 3-3. Touch display. We pour culture medium into the holes.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

          

          


Result ~ E. coli in the touch display ~

 

After incubation, we observed the E. coli by a fluorescence microscope.

 

 

figure 3-5. Images from fluorescence microscope. E. coli on left image is more bright than right one

 
The touch display successfully regulated GFP expression in E. coli !
                     

4 Low pressure-inducible promoter

Figure 4-1. - Pressure response of Plac

It is known that lac promoter is induced under 30 MPa (T. Sato et al., 1995). However, 30 MPa is too high to push with the fingers.
Therefore, we tried to develop low pressure-inducible promoter.











Methods

We tried to develop a low pressure inducible promoter by PCR random mutagenesis to lac promoter. Then we screened an E. coli library, with flow cytometry, for promoters that are induced under low pressure. This scheme is based on the ability to separate bacteria, with a flow cytometer, in response to expression, or lack of expression, of a fluorescent marker.

Results - Sequence and Characterization -

We finished step 1. Fluorescent and non-fluorescent bacteria were sorted and we characterized their promoter.

We sorted fluorescent (A) and non-fluorescent bacteria (B) with a flow cytometer. Then, we analyze these base sequences.

Therefore, fluorescent bacteria have no mutation in CAP binding site, -35 or -10.


5 Write/Erase cycle

figure5-1. Write/Erase cycle

While we can implement write-function, we want to implement additionally erase-function and memory-function. Erase-function enables us to erase the painted picture, and memory-function enables us to keep the picture after we stop induction. We call these functions "Write/Erase cycle". In order to implement Write/Erase cycle, we tried to construct genetic toggle switch.

Genetic toggle switch to implement Write/Erase cycle

figure 5-2. Genetic toggle switch
  1. Write-function
    1. 30 MPa pressure activates Plac.
    2. Plac expresses CI and GFP.
    3. CI represses PL and decreases LacI expression.
    4. Low LacI expression increases Plac activity. ⇒ Bright!!
  2. Erase-function
    1. The heat activates PL.
    2. PL expresses LacI.
    3. LacI represses Plac.
    4. Therefore, GFP expression decreases.

Mathematical model

Why did we use mathematical model?

figure 5-3. Left If PL is not activated or is a bit, write-function is available. Right If PL is activated too much, write-function is not available

As mentioned above, it is known that Plac is activated 94-fold under 30 MPa while we didn't know the increase of PL strength under 30 MPa. If PL is activated too much and Plac activity is weaker than PL activity, we can't implement write-function. So, how much is the range of the increase of PL activity under 30 MPa so as to become advantageous to that of Plac? To know this range, we need to use mathematical model.


Classical toggle switch model

Our mathematical model under atmospheric pressure is equal to a classical toggle switch model shown in figure 5-4. nCI is the cooperativity of repression of the lambda promoter, nLacI is the cooperativity of repression of the lac promoter, αPL is the effective rate of LacI synthesis and αPlac is the effective rate of CI synthesis. nCI and nLacI are called "Hill coefficient". αPL and αPlac depend on strength of promoter-RBS, and are adjustable. Identifying value of nCI and nLacI are required for the modeling. But we know nCI = 3.0 (T. Tian et al., 2006). So, we measured fluorescence intensity various IPTG concentration to identify nLacI.


Identification of nLacI

By testing how LacI represses the lac promoter, Hill coefficient of lac promoter should be decided. In order to adjust effective concentration of LacI, IPTG was added.

GFP fluorescence intensity was enhanced in an IPTG-dose dependent manner. It indicates that the LacI repression was getting weaker by adding IPTG. The characteristics of the lac promoter were calculated by fitting Hill function to the plots shown in figure 5-5, Finally, we obtained nLacI = 2.2.


Conditions for bistability

We calculated the range of αPL in which a toggle switch model is bistability. Here, we set αPlac = 3.0. The result is below.


figure 5-5.PL - RBS strength range from 2.4 to 7.8

Pressure model

figure 5-6. Pressure-inducible genetic toggle switch model

We proposed pressure-inducible genetic toggle switch model which has additional parameters to the classic toggle switch model. These parameters show the increase of activity by pressure (β(p)Plac or β(p)PL). Under atmospheric pressure (0.1 MPa), β(0.1)Plac = 1.0 and β(0.1)PL = 1.0. On the other hand, under 30 MPa, β(30)Plac = 94 and β(30)PL was not known.

In order to implement write-function, the transit of the system from bistability to monostable (Plac is stronger than PL) by 30 MPa pressure is required. Therefore, we calculated the range of β(30)PL which satisfies the above conditions.

The feasibility of implementation of Write/Erase cycle

figure 5-7. The domain of appropriate parameters if αPlac = 3.0

According to the result of simulation, we found that we can implement Write/Erase function even if PL is activated 2.5-fold when αPL = 7.8.

figure 5-8. Pressure-response ability of PL

We identified β(30)PL = 1.4 by our wet experiment under 30MPa pressure (figure 5-6). Therefore, we can implement Write/Erase cycle if we choose an appropriate PL - RBS strength.