Destruction system implementation
We do not want our bacteria to colonize human gut, or to spread in the environment. Thus we will need to add a destruction system in ourIron Coli. Here are some exemple of systems we could use:
• Kill-switch
Kill-switch are one of the most know destruction system and are frequently used in the iGEM competition (see the database created by Paris Bettencourt 2012 team). As we designed a capsule to deliver our Iron Coli in a viscous matrice (with HPMC), we could imagine to incorporate a molecule that will repress the kill-switch. Once the viscous matrice is no longer on the intestines, and so our repressor molecule, the kill-switch would be activated, and then kill the bacteria that remain in the guts. A suitable kill-switch would be for exemple the Biosafety-System araCtive system developed by Biefield 2013 team, which is repressed by L-rhamnose.
• Unnatural amino acids
It is possible to introduce unnatural amino-acids (UAA) with orthogonal system. As for the kill-switch, the orthogonal system would be regulated by the presence of a molecule in the viscous matrice. Then we could use in 2 different ways. First, we can add UAA in our enterobactins enzymes genes. When the molecule is no longer in the intestine, the orthogonal system would no longer be produced and so our different enzymes. Then we can also use UAA as a kill-switch by mutation of an essential gene, exemple Tyrosyl tRNA synthetase, that would be expressed only on the presence of our molecule. Without the recquired molecule, our Iron Coli will die. For more detail, see P.A.S.E 2 System designed by BGU Israel 2013 team.
Chromosomal integration
Horizontal transfer, intra or inter specific, is very common with bacteria. To limit this problem, we could integrate our systems directly into bacterial chromosom of our Iron Coli, thus stopping at least plasmid transfer with the microbiom.
Enterobactin engineering
Even if we made a safe Iron Coli using previous system, a major issue remains: enterobactins produced by our bacteria are released in the lumen of the duodenum and can be catch by both non-pathogenic and pathogenic bacteria. To settle this problem, we could engineer our enterobactin, with slightly modifications, to make them exportable by our Iron Coli but non-importable for any bacteria. Thus, enterobactins would chelate iron and be eliminated in the bowels without inducing modification of the microbiom.