Part:BBa_K523013:Experience

As we (EPFL 2013 team) used the Biobrick BBa_K523013 for our project, we have decided to improve it by better characterizing it. The group that made it was not able to prove with certainty that the YFP was exported to the outer membrane of E.Coli thanks to INP. In order to see the location of this fluorescent protein, we performed microscopy with a confocal microscope.
Competent cells were transformed with this part and grown on a plate with the correct antibiotic. After overnight growth, colonies were picked and dissolved in LB, then grown until an OD of between 0.6 and 0.8.
The fluorescence was directly observed with a YFP filter. We expected to see fluorence only at the membrane, but the resolution was not sufficient to see where exactly the fluorence was located. We determind approximately 30% of the cells to be fluorescent.

Figure 1 : transformed E.Coli excited at 514 nm(excitation wavelenght for YFP)

Figure 2 : zoom on a single transformed E.Coli excited at 514 nm(excitation wavelenght for YFP)

Another interessant point was cluster of fluorescent dots in the transformed bacteria. In the literature ([http://www.ncbi.nlm.nih.gov/pubmed/?term=Clustering+of+ice+nucleation+protein+correlates [1]]) we found that the ice nucleation protein forms aggregates in the cell membrane, so we assume we see this phenomena. (image confocal 3 and zoom4)

Then, to have a clear idea of the localization, cells were incubated with an anti-GFP antibody (YFP and GFP being really close, antibodies can be used for both molecules) and washed several times after. The following results were observed :

figure 3 :
transformed E.Coli with BBa_K523013 excited to see YFP fluorescence (514nm)

figure 4 :
transformed E.Coli with BBa_K523013 incubated with anti YFP antibody, excited to see antibody antiYFP fluorescence (650nm)

figure 5 :
transformed E.Coli with BBa_K523013;merged image of YFP and antiYFP fluorescence

As we can see, the antibody binds at the outside of the bacteria, since it is way to large to enter the cells. The points nicely co-localize with the YFP fluorescence and prove its external localization, since otherwise antibody could not have reached it if it was inside the cell.
With all this proof we concluded that the INP-YFP fusion protein is actually exported to the outer membrane of E.coli.

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