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From 2012.igem.org

Ideally, after the use of the Food Warden system we would like the bacteria to kill themselves when they are not useful anymore. This to ensure the safety of the sticker. As many iGEM teams before us, we thought about an internal kill switch from the start of our iGEM project. That is why we already discussed this briefly in the safety page.

Our future plan is to place a Bacillus subtilis specific toxin gene behind the promoter of a stress factor that responds to nutrition limitation of the Bacillus subtilis. It is most likely that the Bacillus subtilis cells will be influenced by nutritional stress because our sticker is a closed system and only an x amount of nutrients is available. For this kill switch, timing is really important: when the Food Warden bacterium is activated, it will germinate and respond to volatiles of meat that starts to spoil, providing the user with information about the freshness of the meat. However, the growth of the bacteria will continue after the consumer has used our product. Limiting factors for growth will present themselves in time, one of these being limitation of nutrients. Modeling could predict when the most optimal timepoint is achieved. At this time point the stress factor will be triggered and instead of the normal response, a toxin will be produced which kills the cells.

We could also decide to use the Violacein pigment (BBa_K274002), this is a pigment that is naturally toxic to Bacillus subtilis. After the pigment production, the user knows that the meat has started to spoil and subsequently the cells are automatically killed due to the pigment. However, if the pigment is not produced, for instance when there is fresh meat available, this might be a disadvantage because the cells will continue to live.

Besides using an internal kill switch, we also thought about alternative solution to kill the bacteria, by using a chemical reaction. Our first idea was to incorporate a third compartment inside the sticker, containing a antimicrobial substance. After using the sticker, the user breaks this third compartment, thereby mixing the desinfectant with the cells, which results in the killing of the cells. In this case, we should clearly mark the compartments of the sticker to avoid that the user breaks the wrong compartment before use.

References

1. Production of Antibacterial Violet Pigment by Psychrotropic Bacterium RT102 Strain Yoshitoshi Nakamura*, Chikako Asada, and Tatsuro Sawada BIOTECHNOLOGY AND BIOPROCESS ENGINEERING Volume 8, Number 1 (2003), 37-40, DOI: 10.1007/BF02932896