Part:BBa_K1045013:Experience
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Applications of BBa_K1045013
This composite part is functional as indicated by the characterization experiments of our DarR reporter system BBa_K1045017. For this, we used BBa_K1045013 as a control plasmid. Without DarR, gfp was expressed. With DarR (but without c-di-AMP!), gfp expression was turned off. The characterization experiments for BBa_K1045017 are described below:
Microscope Data
For characterization, E. coli BL21 was transformed either with BBa_K1045017 or with BBa_K1045013 as a control. Both strains were grown in the abscence of c-di-AMP and subjected to fluorescence microscopy.
In BBa_K1045013, gfp is placed downstream of a strong promoter and the DarR operator. This vector does not encode for DarR. The strong fluorescence of the cells transformed with BBa_K1045013 (Fig. 1 top) indicated that GFP was expressed. However, when transformed with BBa_K1045017 (Fig. 1 bottom), the cells showed almost no fluorescence. In contrast to BBa_K1045013, BBa_K1045017 encodes for DarR. The low fluorescence suggested that DarR was expressed and active as a repressor down-regulating gfp transcription. Moreover, the results suggested that the control construct BBa_K1045013 was functional as it allowed GFP expression and regulation by DarR.
Experimental details: E. coli cells were grown in LB medium until log phase. A culture aliquot was prepared on slides covered with 1 % agarose (in water) and the cells observed under the fluorescence microscope. For all images, the same exposure time was used. Microscope: Axioskop 40 FL fluorescence microscope; Camera: digital camera AxioCam MRm; Software for image processing: AxioVision Rel version 4.8 (Carl Zeiss, Göttingen, Germany); Objective: Neofluar series objective (Ă100 primary magnification); Filter set: eGFP HC-Filterset (band-pass [BP] 472/30, FT 495, and long-pass [LP] 520/35; AHF Analysentechnik, TĂŒbingen, Germany) for GFP detection.
Characterization of the Reporter System in a Multi-Well Plate Reader
We furthermore analyzed the growth and the fluorescence over time of the BL21 E. colis we transformed with the DarR reporter system construct BBa_K1045017. As a control, we employed E. coli cells harboring the BBa_K1045013 plasmid.
Using the plate reader, we quantified the strength of the DarR construct in E. coli. A dilution series of c-di-AMP (0, 50, 100, 150, 300, 500 and 1000 nmol c-di-AMP) was used to test the reaction of the DarR reporter system to the nucleotide.
Fig. 2 shows the growth curves recorded via the optical density (OD) at the wavelength 600 nm. The GFP fluorescence was measured at 509 nm over the time, as well. Since the fluorescence depends on the growth of the E. coli cells, the GFP fluorescence was normalized to the OD at 600 nm for each time point (Fig. 3). All graphs show the mean value of three technical replicates of one biological replicate. The error bars indicate the standard deviation.
Experimental setup: total time 21 h; 15 min measurement interval; 37°C, medium shaking; 96-well titer plate; Synergy Mx Monochromator-Based Multi-Mode Microplate Reader; Gen5 V2.01
As in the microscope experiments described above, the expression of the reporter was prevented (even without c-di-AMP), when DarR was encoded in the vector. This data suggested that DarR was expressed and active. In addition, the composite part BBa_K1045013 was functional as it allowed GFP expression that was shut down by DarR.
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