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Safety
![](https://static.igem.org/mediawiki/2018/2/23/T--Tongji_China--picture-Safety-Light_Control-0.png)
Light-off system
We use the light-off system from 2017 SSTi-SZGD to kill our bacteria after effecting.
It contains two parts.
The switch
One is a light-repressed system containing a single light repressor LexA-VVD, and a ColE promoter containing an SOS operator sequence for LexA binding, regulates the expression of target genes.
The Killer
![](https://static.igem.org/mediawiki/2018/8/85/T--Tongji_China--picture-Safety-Light_Control-2.png)
In general, it forms a light switch and a killer to control the lives of our bacteria, it confirms the safety of our whole project.
After our bacteria are released in the gut environment for several hours, they can be eliminated by our immune system. Our project uses this method to ensure the bacteria to be dead the time they are released into the environment. It can be safe for humans and friendly to the environment.
Then we conduct some experiments to verify the kill-switch's function.
However, the amount of the P. aeruginosa does not show significant reduction after the lighting. We indicate that the plasmid electrotransformation may be not quite successful. Or may because the type of bacteria--Pseudomonas aeruginosa has not been used in this method before, and the plasmid vitality in the bacteria is lower than in Escherichia coli. We are searching for other reasons, like the promotor strength, codon degeneracy and so on. We will solve the problem in the future.
References:
[1] Chen X, Liu R, Ma Z, et al. An extraordinary stringent and sensitive light-switchable gene expression system for bacterial cells. Cell Res. 2016;26:854–857. doi: 10.1038/cr.2016.74.
[2] Trewin AJ, Berry BJ, Wei AY, et al. Light-induced oxidant production by fluorescent proteins. Free Radic Biol Med. 2018 Nov 20;128:157-164. doi: 10.1016.
[1] Chen X, Liu R, Ma Z, et al. An extraordinary stringent and sensitive light-switchable gene expression system for bacterial cells. Cell Res. 2016;26:854–857. doi: 10.1038/cr.2016.74.
[2] Trewin AJ, Berry BJ, Wei AY, et al. Light-induced oxidant production by fluorescent proteins. Free Radic Biol Med. 2018 Nov 20;128:157-164. doi: 10.1016.