Native N-3-Oxo-Hexanoyl-l-Homoserine Lactone tests using the Tecan Infinite M200 PRO™ plate reader

File:Gfp od sigmoid1.png

In order to select mutated pLuxR promoters we need to know about the sensivity of the wild type construct. The test range was inspired form the paper about [http://www.ncbi.nlm.nih.gov/pubmed/18760602 Evaluation of a focused library of N-Acryl L-Homoserine lactone reveals a new set of potent quorum sensing modulators].The paper shows sensivities of the pLuxR promoter to different sets of OHHL molecules in Vibrio fisheri. We need to adjust the ranges for our E.coli DH5alpha strain in a second run and finally get our sensivity curve over the linear range of [0 nM],[0.25 nM],[0.5 nM],[1 nM],[2 nM],[3 nM],[4 nM],[5 nM],[10nM],[20 nM],[30 nM],[40 nM]and[50 nM].

The experimental set-up includes a 96-well plate filled with 180 uL LB media , 10uL of receiver cells and 10 uL of different OHHL concentrations, everything in triplicates. (+ blank and negative control). The experiment runs for 16 hours in order to monitor the evolution of fluorescence and later choose the steady state to create the sensivity curve.The data are analyzed with GraphPad Prism 6.0.

PluxR random mutagenesis PCR

The pLuxR R0062 wild type promoter was mutated using site directed mutagenesis on specific sites according to the paper [put paper here]

PluxR promoter with different sensitivity analyzed using the single cell analyzer BD LSRFortessa™ Flow Cytometer System

To gain precise data out of our fluorescence analysis, to better characterize the different promoters, we use the single analysis to obtain high throughtput data.
The protocol was the following :
From overnight cultures we inoculate 50mL Falcon™ tubes containing 5mL LB media, 5uL OHHL and the antibiotic. We evaluate a range of 10 different concentrations from
10^-4nM OHHL to 10⁵nM OHHL by a 10 fold increase, according to the results of the plate reader analysis. The measurements were done in duplicates.

Figure 2: Sensitivity curve of the Wild Type using the BD LSRFortessa™ Flow Cytometer System. The first graph on the left is the fluorescence(au) against the concentration (nM). The second graph shows the fluorescence(au)over the whole range OHHL concentrations.

Figure 3: Sensitivity curve of the PluxR1 (G1) mutated promoter using the BD LSRFortessa™ Flow Cytometer System. The first graph on the left is the fluorescence(au) against the concentration (nM). The second graph shows the fluorescence(au) over the whole range OHHL concentrations.

The first graph (on the left)of Figure 2. is the sensivity curve of the J08955-GFP construct with the wild type R0062 promoter. The EC₅₀ indicates the half maximal effective concentratio and is 0.02nM for the wild type. We had a few background noise during the fluorescence measurements of the wild type construct, that's why the R²=0.8.
The second graph (on the right)of Figure 2. is the fluorescence in function of the side scatter over the whole concentration range of OHHL. The side scatter is a measurement of refracted light that occurs at each interface in the cell. The refracted light is collected and amplified in a photomultiplier tube. The SSC gives information about the cellular granularity and complexity (e.g. dead cells).
In the end we note that the EC₅₀ (0.02nM) from single cell analysis is 100 times lower than the EC₅₀ (2nM) calculated out of the Tecan Infinite M200 PRO™ plate reader measurements

The first graph (on the left)of Figure 3. shows the sensivity curve of the isolated pLuxR1 (or G1 according to the deepwell plate identification). The EC₅₀=6'250nM is remarquably high andwell correlating data according to R²=0.97. The second graph (on the right)of Figure 3. is the fluorescence in function of the side scatterover the whole concentration range of OHHL

Figure 4. Comparison of the Wild Type and PluxR1 mutant sensitivity curves using the BD LSRFortessa™ Flow Cytometer System

The direct plot of both sensivity curves shows the clearly shifted sensivity of the pLuxR1 promoter in comparison to the wild type R0062 promoter. The EC₅₀ shit from 0.02nM for the wild type to 6'250nM for the pLuxR1 promoter is equal to a 312'500 fold increase.
This promoter will be used in our final set-up to only respond to high concentrations of OHHL and therefore be activated, when two sender cells are surrounding the receiver cell, and expressing the AES hydrolase responsible for the colorimetric conversion of the specific substrate to a visible purple output.

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