$\Tgo$he main concerns raised by $\MyColi$ depend more of the protein that we chose to produce than of $\MyColi$ itself. However, $\MyColi$ could compel an escaped recombinant bacterium to produce an industrial protein in the environment, when a bacterium without our system would quickly degenerate and stop producing the protein of interest. The risk seems thin, since such an overproducing bacterium would suffer from a clear competitive disadvantage in a wild environment, but it is not excluded that the plasmid containing the $\MyColi$ system maintains itself anyway through $\small Horizontal$ $\small Gene$ $\small Transfer$ (HGT), at the expend of the wild bacteria it infects, benefiting of the proprieties of the TA system.
However, in the current state of our project, the plasmids are maintained in the bacterial population through the usual system of antibiotic resistance, since the toxin and the antitoxin are to be placed on different plasmids bearing different resistance genes. The properties of the TA systems are only used to boost protein production, not plasmid stability. The system will thus decay quickly if $\MyColi$ bacteria wander in a wild environment, without any antibiotic. Furthermore, in the final version of our project (that is, if we have the time to go this far), the toxin gene will be inserted in the genomic DNA of the bacteria, preventing it to ever be lost, and compelling the bacteria to keep the plasmid bearing the genes of the antitoxin and the protein of interest . It will also prevent any reasonable chance of HGT of the $\MyColi$ System.
If, for one reason or another, the overproduction of a protein did not results in a competitive disadvantage, one could also subordinate antitoxin production to an inducible promoter that would act as a built-in biocontainment device. Indeed, if we chose an artificial inducer for the expression of the antitoxin (that is, an inducer that is not found in nature), an escaped bacterium could not inhibit the activity of the toxin and woud quickly die outside of the bioreactor.
In conclusion, our system seems to be extremely safe and predictable, whose biggest danger consists of being used to produce a dangerous protein. This latter problem should be addressed on a case-by-case basis, by other institution than ours. Of course, our topical lab system is really safe, since it should only overproduce fluorescent proteins (GFP or RFP).
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- Université Libre de Bruxelles -
