- Policy & Practices
All iGEM teams were encouraged to participate in the 3rd Interlab Study. The goal of the Interlab Study is to be able to perform absolute fluorescence measurements instead of relative fluorescence measurements. This year iGEM teams from all over the world compared fluorescence data of test devices provided by iGEM HQ. For more information visit the iGEM Interlab website.
We were provided with five devices, all of these were built into the pSB1C3 backbone, which contains chloramphenicol resistance. There are three test devices, a positive control and a negative control.
- Test Device 1: pSB1C3 backbone containing J23101 (promotor), B0034 (ribosome binding site), E0040 (GFP), B0015 (double terminater)
- Test Device 2: pSB1C3 backbone containing J23106 (promotor), B0034 (ribosome binding site), E0040 (GFP), B0015 (double terminater)
- Test Device 3: pSB1C3 backbone containing J23117 (promotor), B0034 (ribosome binding site), E0040 (GFP), B0015 (double terminater)
- Positive Control Device: pSB1C3 backbone containing I20270 (GFP expression device)
- Negative Control Device: pSB1C3 backbone containing R0040 (no GFP expression device)
To obtain reference values of the fluorescence measurement of our plate reader, iGEM HQ provided us with Fluorescein Isothiocyanate (FITC). With serial dilutions of this protein reference fluorescence measurements could be made.
To calibrate the OD600 (density/number of cells) we used water and a mono-dispersed silica suspension (LUDOX), also provided by the iGEM HQ. The OD600 difference between those two and a reference value from iGEM HQ yielded a correction factor for the OD600 that was used to correct the OD600 measurements of the test devices.
The host for each device was E. Coli strain BL21(DE3). The promotors in the vector were constitutive meaning no protein expression inducer was needed.
First the test devices were transformed in BL21(DE3), after overnight growing, two colonies were picked to grow small cultures. When the bacterial cultures of the test devices had grown overnight, they were diluted with LB medium to an OD600 of 0.02. Then every hour a sample was taken from each culture over a time span of six hours. From every sample the OD600 and fluorescence was measured. The samples were stored on ice before the measurements were done, so the measurement of the samples could be done simultaneously.
The Tecan Spark M10 plate reader was used for the measurements. All measurements were done with a volume of 100 µL per well. The measurements were corrected by subtracting them with a blank measurement, this blank was LB medium with chloramphenicol.
Below are the results of the OD600 calibration with water and LUDOX and the fluorescence reference measurements using serial dilutions of FITC.
From the fluorescence and OD600 data it can be deduced that the promotor of device 1 is the strongest promotor, because it shows the highest fluorescence. Followed by the promotor of device 2, with slightly lesser fluorescent. The weakest promoter was from device 3, it had the lowest fluorescence.
- Data OD600
- Data fluorescence
- Data fluorescence/OD600