The Project, Mercuro-Coli

Introduction

With industrial growth, wastes are accumulating and the presence of pollutant and toxic compounds is becoming an international concern.

In this context, we present Mercuro-Coli, an easy-to-use biosensor for the in situ detection and quantification of mercury into polluted water. Intended to fieldwork applications, the device should be very easy to handle:

• Unpack the plate.
• Deposit the polluted water sample.
• If mercury is present, a red stripe appear, its position indicates the amount of pollutant.

Specifications

At the beginning of the project, we defined a certain number of specifications for the device:

• Operating living cell: E. Coli: BW 25 113
• Only one type of bacteria containing the whole genetic circuit.
• Form a biofilm on the plate with E. coli bacteria containing the designed genetic circuit.
  This point was revised according to modeling results. A device with channels containing bacteria instead of a biofilm has been chosen.

• Comparative measure:

The comparative measure will be made by comparing mercury concentration to IPTG concentration. IPTG concentration will is the reference. So, an IPTG gradient concentration will be made beforehand in the plate constituting our scale of quantification.

By adding uniformly the polluted sample, two different bacterial behaviors will come up depending on the predominant concentration:

On the left side, where the mercury concentration is prevailing, bacteria with a sending behavior will appear. They have the ability to release in the external medium Quorum Sensing molecules, AHL, thanks to the expression of the CinI protein. On the right, where the IPTG concentration is dominant, bacteria with a receiving behavior will come up. They express CinR protein, a cytoplasmic receptor for Quorum Sensing.

So, we will have the emergence of two distinctive areas separated by one boundary that can appear closer to one side or the other depending on the quantity of mercury. For example, if the sample contains less mercury the boundary will appear closer to the left side.

So, the location of that boundary represents our point of interest that we will try to visualize.

• A visual result:

The two different behaviors were chosen in purpose.

At the boundary,Quorum Sensing molecule, AHL, released by sending bacteria will be received by the front of receiving bacteria. The complex formed by AHL molecule and CinR protein will then induce the coloration of the front receiving bacteria.

Let's go further to understand how such evolution of this system is possible with only one strain ?