Network details

Our system is divided in two modules:

a signaling module
an amplification module

The signaling module

The signaling module allows our bacteria strain to integrate the input signal = the pathogene presence.

This is a modelized module.

The idea behind this module comes from the iGEM London Imperial College 2010 Team's work on Parasight [1].

Staphylococcus aureus secretes the exfoliative toxin B [2] which cleaves a specific amino-acids sequence (Desmoglein 1). This specific sequence can be used as a linker between a membrane protein and a dipeptide.
Once S. aureus is present, the linker is cut by the toxin and the dipeptide is released.

The dipeptide binds its receptor which was engineered [3] [4] by the team:

the extracellular part of Tap [5] is a dipeptide receptor involved in the chemotaxism
the intracellular part of EnvZ [6] is a histidine kinase involved in the osmoregulation

Once the dipeptide binds the Tap part [7], the intracellular EnvZ part allows the phosphorylation of OmpR [8] [9], which is a constitutively produced transcriptional activator.

OmpR phosphorylation's allows the activation of the OmpC promoter[10].

Amplification module

The amplification module allows our bacteria to amplify the input signal and to produce an output signal = fluorescence.

This is also one of our module of modeling.

Internal amplification

The activation of the OmpC promoter allows the production of Adenyl cyclase [11]. Adenyl cyclase catalyses the conversion of ATP (Adenosine Tri-Phosphate) into cAMP (cyclic Adenosine Mono-Phosphate).

The binding of cAMP to CRP (C-reactive protein) leads to the production of AraC by activating the pMalT promoter [12].
In the presence of arabinose, AraC and cAMP-CRP, cooperatively activate the pAraBAD promoter [13], thus forming an "AND" gate. This allows the production of:

Adenyl cyclase which reproduces cAMP, forming thus an amplification loop
GFP (Green Fluorescent Protein) = our output signal

External amplification

When a bacterium detects S. aureus, it produces a several molecules of GFP and evenmore cAMP. cAMP diffuses through the membrane and activates the amplification loop in all the neighbouring bacteria [14], which triggers the production of GFP and cAMP.
This leads to an entire population which produces GFP where only a bacterium detected the pathogen in the first place: