| - | content.text= "Our system of light inducible protein degradation can be utilized to degrade any specific protein and is therefore usable to realize a light induced kill-switch system. Therefore a connection between the degradation system and an toxin-antitoxin module like MazEF or ccdA/ccdB is needed. You could either light inducible degrade the toxin or the antitoxin by adding an ssrA-tag to its encoding gene, that is detected by our degradation system: <ul><li><b>Using the degradation of the toxin:</b> For that purpose the insertion of a plasmid containing the ssrA-tagged toxin encoding gene is needed. As the predominance of the toxin leads into a cell death pathway in bacteria, a bacterium containing a module that allows light inducible degradation of the toxin would only relive, when the toxin is light induced degraded. When light turns off, the overexpression of the toxin is no longer compensated and the toxin leads the bacterium into apoptosis. Apart from the use in lab security such a kill-switch system would also be useful in environmental applications of bacteria, as you can control the time those bacteria are living and you avoid that they may live in areas where no light is. If you e.g. want to use bacteria in a lake to improve its ecological stability you could be sure, that after one night all genetically modified bacteria are dead.</li><li><b>Using the degradation of the antitoxin:</b> Two plasmids are needed: The first one needs to express the toxin and the second one the ssra-tagged antitoxin, so that the amounts of the toxin and the antitoxin are in equilibrium. If light induces the degradation system, the antitoxin is degraded and the predominant toxin will kill the bacterium. </li></ul> Regarding our idea to improve lab security by inserting a kill-switch system, both described ways seem possible. Using the first one, you need to cultivate and work with the bacteria steadily under blue light, as darkness would kill them. Realizing the second one, you must avoid any blue light in the lab. If bacteria get into touch with daylight our any blue light, they will be killed. As we suppose our light inducible degradation system to be activated via daylight, using the degradation of the toxin for lab security would be unlikely. Bacteria that escape from the lab could go on living simply by getting into touch with daylight. So finally we focused on the second system (via the degradation of the antitoxin).</br> We described the realization of a light inducible kill-switch system via the insertion of plasmids into bacteria, but we also consider a final kill-switch system to be realized in the genomic DNA, as it would raise the security of such a system. Plasmids in bacteria can get lost, for instance via cell division, whereas a genomic DNA mutation is less probable.</br>Finally we have to add that we consider a MazEF or ccdA/ccdB kill-switch system to be a part of a much larger system in bacteria, that raises lab security. This system should contain much more than one kill-switch system to compensate errors of single kill-switch systems.";
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