Team:Grenoble/Projet/Design/quorum

Quorum sensing is an important phase of physiological development of the bacteria. It’s the communication signal between bacteria carried by a signalling molecule. All bacteria can produce or detect the quorum sensing molecule. Quorum sensing involves a secreted molecule which allows the number of bacteria to be known and give a logical response to a high level of population. Frequently the Quorum sensing is the signal to stop the growth, activate the virulence state, or activate luminescence.

The quorum sensing (QS) detection is links to his concentration in the medium, so when the bacteria are in low numbers the QS molecule is at a low concentration and does not activate the response. But when the bacteria become too abundant the QS concentration is higher and activates the response.

Beginning of growth phase, cells are few, so the production of QS is very low, no response activity. Middle Growth phase bacteria are many but not enough for activate QS response, the concentration in QS is not high enough. In Stationary phase, bacteria are very concentrated so the production of QS is maximal and the lack of space up the concentration of QS. Both phenomena are sufficient to activate a response.

The Quorum sensing system is composed of three elements: an enzyme, a secreted molecule and a receptor.

A bacterium synthesises this Quorum sensing enzyme which in turn synthesizes the quorum sensing molecule. This molecule diffuses within and outside the cell (around 1mm/h), and can enter inside the issuing bacterium or any other bacteria in its neighbourhood. The QS molecule interacts with its receptor protein. The complex binds to DNA and activates or represses genes generating the appropriate response.

The Quorum sensing (QS) is an important part of our project because ours cells have the same genetic network, but they have the ability to choose a pathway and become sender cell or receptor cell of quorum sensing (QS), depending the IPTG and Anhydro-tetracyclin (ATC) concentration in the medium. Remember bacteria are fixed on a plate, at one side bacteria are in a way and at the opposite side they choose the other way. So at the interface of these two populations, we are in a cryptic place, the concentration are in a specific ratio and bacteria have the same probability to choose one of the both ways. We obtain closely, a mix of QS senders and QS receptors.

The receptor cells receives quorum sensing molecules from the senders, the presence of receptors proteins (in receptor cells) and QS molecules, permit by complexing both to activate the transcription of the pCin promoter which regulate the synthesis of a orange pigment named lycopen. So at the interface of populations we can observed a red line corresponding to a defined concentration in anhydro-tetracyclin(ATC).

The interface location move on the plate depending of the concentration ratio of IPTG and ATC.