RESULTS

Characterisation of the CpxR & split IFP1.4 stress-sensitive response

Experiment 1: Promoter characterisation and folding ability of fused GFP to CpxR via 10 amino acid 2 x (GGGGS) flexible linker

Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, commodo vitae, ornare sit ameh2t, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. Donec non enim in turpis pulvinar facilisis. Ut felis. Praesent dapibus, neque id cursus faucibus, tortor neque egestas augue, eu vulputate magna eros eu erat. Aliquam erat volutpat. Nam dui mi, tincidunt quis, accumsan porttitor, facilisis luctus, metus

Experiment 2: CpxR dimerization & Dimerization Orientation

Introduction
CpxR is the relay protein in the stress resonsive CpxAR two component regulatory system. It has been shown by split beta galactosidase assay that CpxR dimerizes when phosphorylated (activated) in yersinia pseudotuberculosis. Moreover, following other in vitro FRET studies, it was shown that E.Coli CpxR interacted with itself. We therefore hypothesised that dimerization would also be true in vivo in E.Coli.

Aim
This experiment aimed to determine if and how CpxR dimerised in vivo in E.Coli. This experiment intended to get a first idea of the real-time temporal dynamics of the activation of CpxR (the cytoplasmic relay protein of the CpxA-R pathway) by KCl stress via CpxA (the periplasmic sensor protein of the CpxA-R pathway). This experiment is a first of its kind.

Methods
To evaluate if and how CpxR dimerized under KCl stress, we built four constructs with the various possible orientations that the split IFP1.4 fragments could have with CpxR: IFP[1] and IFP[2] on the N-terminus of CpxR, IFP[1] on the N-terminus of CpxR and IFP[2] on the C-terminus of CpxR, and finally IFP[1] and IFP[2] on the N-terminus of CpxR. The protocol for this experiment can be downloaded here.

Results
As shown in the graph bellow, we successfully proved that CpxR dimerized in vivo and that dimerization led to close interaction of its C-terminus. As seen in the graph, induction of the signal was done at minute 24 (marked via a vertically spoted line). It is to be noted that the signal is immediate (3 fold increase in 2 minutes) and that the signal overall increased 30-fold. This finding is important as CpxR is part of the highly conserved OmpR/PhoB subfamily - especially for their C-terminus. This system could be used to study various other components of the OmpR/PhoB subfamily and thus lead to a new generation of highly senstitive and reactive biosensors.

Experiment 3: Signal induction by various concentrations of KCl & signal shutdown by centrifugation

Aim
Having found that KCl was a good signal inducer for our signal, we decided to characterise our biobrick by testing if the signal could be modulated by various concentrations of KCl and if we were able to remove the signal by centrifugation and medium change. To do so, we read our signal for 20 minutes without stress and then added KCl. At minute 144 we centrifuged our cells and replaced the medium with PBS to be able to get a shutdown of the signal.

Methods
To evaluate if a modulation in KCl concentrations affected the intensity of the intensity of the fluorescent signal, and if a change in medium by centrifugation shutdown the signal; we read our signal on a plate reader for 20 minutes without stress and then added KCl. At minute 144 we centrifuged our cells and replaced the medium with PBS to be able to get a shutdown of the signal. The protocol for this experiment can be downloaded here.

Results
We successfully showed that increasing concentrations of KCl led to stronger signals up to a saturation concentration of about 80 mM KCl. Moreover we were able to shut the signal down, thus proving the reversibility of our system. These results prove the reversibility of the split IFP1.4 and suggest that real-time temporal dynamics analysis are possible for our system.

Experiment 4: Visualization of the the CpxR split IFP1.4 activation by KCl stress

Aim

Results

Experiment 2: CheY/CheZ fused to split firefly/renilla luciferase, and full firefly/renilla luciferase characterisation

Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, commodo vitae, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. Donec non enim in turpis pulvinar facilisis. Ut felis. Praesent dapibus, neque id cursus faucibus, tortor neque egestas augue, eu vulputate magna eros eu erat. Aliquam erat volutpat. Nam dui mi, tincidunt quis, accumsan porttitor, facilisis luctus, metus

Experiment 5: Microfluidic stuff ?

Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, commodo vitae, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. Donec non enim in turpis pulvinar facilisis. Ut felis. Praesent dapibus, neque id cursus faucibus, tortor neque egestas augue, eu vulputate magna eros eu erat. Aliquam erat volutpat. Nam dui mi, tincidunt quis, accumsan porttitor, facilisis luctus, metus

Experiment 5: Yeast stuff ?

Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas. Vestibulum tortor quam, feugiat vitae, ultricies eget, tempor sit amet, ante. Donec eu libero sit amet quam egestas semper. Aenean ultricies mi vitae est. Mauris placerat eleifend leo. Quisque sit amet est et sapien ullamcorper pharetra. Vestibulum erat wisi, condimentum sed, commodo vitae, ornare sit amet, wisi. Aenean fermentum, elit eget tincidunt condimentum, eros ipsum rutrum orci, sagittis tempus lacus enim ac dui. Donec non enim in turpis pulvinar facilisis. Ut felis. Praesent dapibus, neque id cursus faucibus, tortor neque egestas augue, eu vulputate magna eros eu erat. Aliquam erat volutpat. Nam dui mi, tincidunt quis, accumsan porttitor, facilisis luctus, metus