The aim of our project is to concentrate a significant population of bacteria around a vegetable polysaccharidic surface, a non-difussible signal. This phenomenon was renamed as Bacterial Crowding. Therefore, it is necessary that the process of interaction with the surface by a few number of bacteria triggered the production and excretion of chemicals that, acting as chemoattractants, generate a chemical-diffusing gradient which could induce chemotactic process of close bacteria. These bacteria will redirect their random movements to the same plant surface and the concentration of the cell population will raise up in this region, thanks to an amplification process.
In order to get that effect it is necessary to use the Prh system, the only known sensing system able to detect non-diffusble signals. We also used the Fec system to design four signal transduction circuits which would finish with PrhI-dependent promoter PprhJ, which would activate specifically chemoattractant production (aspartate, glutamate or salicylate); or with FecI-dependent promoter PfecA, which would act in the same way. You can see these circuits here. However, we finally only focused on one signal transduction circuit which uses PrhA/FecA outer membrane fusion protein, performing an hybrid sensing system.
This project could use one or two bacterial strains, depending on the chemoattractant. If it is aspartate or glutamate it would be necessary only an E. coli population that uses as chemotactic receptor Tar. If we use salicylate as chemoatracttant, the system will be composed by two bacterial strains: Escherichia coli (detection and signaling population) and Pseudomonas putida G7 (chemotactic population), because the first one is not chemotactic to salicylate.