Team:Evry/Project/Compounds/Sensing

In response of those recent awareness, different systems of detection have been developed.
But with the approach of bio-sensing, we develop tool which are able to detect a pollutant with a very high efficiency, and with a great specificity.
Biological elements necessary to built those tools have a very low cost, are very easy to obtain and the assembling is quite easy and don’t emit any pollutant.
So besides having effective and cheap systems, biosensors are totally biological and non-polluting tools.

To devellop our tools, we search in the scientific litterature, some natural systems based on promoters inducibles by our compounds of interest. It's often promoters wich allow the expression of a set of genes which correspond to the cell's response to the compound.
For phenols, an a set of genes called Dmp operon in Pseudomonas CF600 is able to degrade phenol with the aim to produce acetyl CoA, and use these compounds as an energy source.

The transcription of this operon is regulated by the DmpR regulator element which bind phenol and activate the transcription of the phenol hydroxylase promoter by allowing the fixation of the RNA polymerase (more information, see the section Sensors).

Figure7: The catabolic pathway for degradation of biphenyl by aerobic bacteria and the organization of bph gene cluster (Kensuke F., Hidehiko F., 2008) .

Sensing's constructions are very simple and easy to realize. But in a larger framework we can imagine one day be able to clone all the enzymes of the degradation pathway of phenol and PCBs in our bacteria. In fact we can create, more than a sensor system based on sponge, a complete filtrating system which can not only sense pollutants, but totally remove them.

for nitrites it exist different biologic denitrification systems to reduce nitrates concentration in water that use bacteria as Pseudomonas with a denitrification yield of 80%. Bacteria are fixated on a mineral support and feed with acetic acid or ethanol (SNIDE). The major drawback is the production of nitrous and nitric oxide that are greenhouse gas.
To make a bacterium able to transforme nitrite into nitrogen we just have to add two enzymes:
-> Hydroxylamine oxydase from Parococcus denitrificans: nitrite + H2O = hydroxylamine
-> Hydrazine oxydoreductase from Candidatus Brocadia anammoxidans: hydroxylamine + NH3 + acceptor = N2 + H2O + reduced acceptor

Figure8: Nitrogen cycle.

Unfortunately, when we talk about heavy metals we talk about atoms which cannot just be degraded by a biological pathway. But we can imagine some ways of accumulation of these elements in bacteria that we can remove and treated after like chemical waste.