Team:TU Eindhoven/Project/Characterization/Cell Viability


iGEM Team TU Eindhoven 2014

iGEM Team TU Eindhoven 2014

Cell Viability Assay

We showed that the click reaction on the membrane was successful, however the question remains if the bacteria are still alive. For this reason an assay was performed after the click reaction to check the viability of the bacteria.

First, protein expression is induced as described in the protocol for Protein Expression. Cells were resuspended in PBS. Two different batches were tested in this assay to ensure that the outcomes are reliable if they match each other.

For the first reaction, the cells are incubated in a solution of 30 µM DBCO-PEG-10 kDa. Previous experiments have shown that the click reaction on the cell membrane occurs, this confirms that in this solution DBCO-PEG-10 kDa will attach to the cell membrane and therefore is not tested again.

For the second reaction, the cells are incubated in a 30 µM solution of PEG 3350 Dalton. These PEG molecules do not have the DBCO group to click onto the cell membrane. However they have the same influence on the environment in which the cells react. This second reaction was done to simulate the environment in which the click reaction occurs. The only difference between the cells is that in the first case the PEG molecules are covalently bound to the cell membrane, which can have a negative effect on the cell viability. See Protocol cell viability

Table 1. The following tubes were prepared to incubate for 2 hours at 4°C in a shake incubator at 500 rpm.
Tube Name [DBCO and PEG no DBCO] Cells [109 mL-1] DBCO 10 kDa (5 mM) PEG no DBCO 3350 Da (5 mM)
DBCO 1 30 µM 200 µL 1.21 µL 0 µL
DBCO 2 30 µM 200 µL 1.21 µL 0 µL
PEG 1 30 µM 200 µL 0 µL 1.21 µL
PEG 2 30 µM 200 µL 0 µL 1.21 µL

Meanwhile, 12 agar plates were prepared with kanamycin and chloramphenicol to plate the cells.

After the incubation, the samples are diluted to the required concentration of cells before plating. Concentrations of cells needed for these plates are approximately 1000, 100 and 10 cells.

After diluting, 100 µL of each sample was plated on an agar plate and incubated for ~16 hours at 37°C.

The next day the plates were analyzed. For every plate the colonies were marked manually and counted. The results are shown in the table below.

Table 2. Results of the analyze agar plates after incubation of ~16 hours.
Tube Name Number of Cells Plated Number of Colonies Marked % Survival
Dilution DBCO 1_2 1000 321 32.1%
Dilution DBCO 1_3 100 27 27%
Dilution DBCO 1_4 10 2 20%
Dilution DBCO 2_2 1000 343 34.3%
Dilution DBCO 2_3 100 43 43%
Dilution DBCO 2_4 10 6 60%
Avarage DBCO 30%
Dilution PEG 1_2 1000 355 35.5%
Dilution PEG 1_3 100 38 38%
Dilution PEG 1_4 10 1 10%
Dilution PEG 1_2 1000 523 52.3%
Dilution PEG 1_3 100 42 42%
Dilution PEG 1_2 10 4 40%
Average PEG 36%

In this case it is obvious that a part of the cells is still viable in both the reactions. As seen in the results in table 2 there is a small difference between the viability of the cells clicked with DBCO-PEG compared to those without this molecule. However based on the small amount of data and the method of registering the colonies more research is needed to confirm this difference.

With this assay it is confirmed that the membrane can take the stress caused by the molecules clicked on the membrane and are able to survive. It can be concluded that the cells are viable after protein expression and the click-reaction. However, it is not known in which way this specific environment influences the cell viability. Due to the variety of the molecules which can be used for the click reaction the environment changes for every reaction. To check the viability of the cells in specific environments these assay have to be performed again.

iGEM Team TU Eindhoven 2014