Template:Team:Bonn:NetworkData

content.titleLong = "Kill-switch systems using stress-induced toxin-antitoxin modules in Escherichia coli";

content.summary= "Toxin-antitoxin systems are composed by an antitoxin and a toxin coding gene. Connecting our light inducible protein degradation system to the antitoxin via an ssrA-tag allows light induced cell death, as predominance of the toxin in a bacterium activates a cell death pathway.";

content.text= "Our system of light inducible protein degradation can be utilized to degrade any specific protein and is thus usable in a light induced kill-switch system. For this application a connection between the degradation system and a toxin-antitoxin module like MazEF or ccdA/ccdB is needed. Either the toxin or the antitoxin could be light inducibly degraded by adding an ssrA-tag, which is detected by our degradation system, to its genetical code: <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. Since the predominance of the toxin activates a cell death pathway in bacteria, a bacterium containing a module that allows light inducible degradation of the toxin would only be viable, when the toxin is degraded. In darkness the toxin overexpression is no longer compensated and aggregation of it leads to cell death. Apart from the use in lab security such a kill-switch system would also be useful for environmental applications of bacteria, since it opens up the possibility of deploying bacteria for only one day and ensures their passing by nightfall. For example bacteria could be used to perform the ecological stabilization of a lake but after one night any genetically modified bacteria would be dead.</li><li><b>Using the degradation of the antitoxin:</b> Two plasmids are needed: The first one to express the toxin and the second one to express the ssra-tagged antitoxin, in such manner that the amounts of the toxin and the antitoxin are in equilibrium. Once 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 implementing a kill-switch system, both described ways seem possible. Usage of the former would require cultivating and working with the bacteria under constant blue light, as darkness would kill them. Realization of the latter would require no usage of any blue light in the lab since bacteria which get into touch with daylight our any blue light would be killed. Due to the high light sensivity of our degradation system it can most likely be induced by daylight, which renders the former killswitch system useless. Bacteria which escape from the lab could survive simply through contact with daylight. Consequently we focused on the second system (the degradation of the antitoxin).</br> With MazEF we described a light inducible kill-switch system via the insertion of plasmids into bacteria. However a final kill-switch system would have to be introduced into the genomic DNA since plasmids in bacteria can be ejected, for instance via cell division, whereas a genomic DNA mutation is less likely to occur. Nevertheless the risk of a loss of function cannot be eliminated , which is why a secure system should countain much more than one kill-switch system to compensate the malfunction of a single kill-switch system. Therefore, we consider the MazEF kill-switch system to be part of a much larger security system for genetically engineered bacteria. </br>";