Network details

Our system is divided in two modules:

signaling module
amplification module

Signaling module

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

This is also one of our module of modeling.

The idea of this module is du to the iGEM London Imperial College 2010 Team work on Parasight [1].

Staphylococcus aureus secretes an enzyme, exfoliative toxin B [2] which cut 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 protease and the dipeptide is released.

The dipeptide binds to his receptor which is an engineered [3] [4] receptor:

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

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

Once OmpR is phosphorylated, it allows the activation of the OmpC promoter[10].

Amplification module

The amplification module allows our bacterial strain 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 by phosphorylated OmpR allows the production of Adenyl cyclase [11]. Adenyl cyclase is an enzyme which catalyse the conversion of ATP (Adenosine Tri-Phosphate) to cAMP (cyclic Adenosine Mono-Phosphate).

cAMP binds to CRP (C-reactive protein) and then this complex allows the production of AraC by activating the pMalT promoter [12].
In the presence of arabinose, AraC, with cAMP-CRP, activates the pAraBAD promoter [13], forming thus an "AND" gate, which allow the production of:

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

External amplification

When one bacterium detecte S. aureus, it produces a lot of GFP and cAMP. cAMP can diffuse through the membrane and activates the amplification loop in all the neighbourings bacteria [14] which can thus produce a lot of GFP and cAMP.
The result is an entire population which produce GFP whereas only one bacterium has detected the pathogen in the first place: