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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 of any use anymore. This to ensure the safety of the sticker. As many iGEM teams before us, we thought about an internal kill switch and in the safety page [link to safety page] we already discussed the internal kill switch briefly.

Our future plan is to place a Bacillus specific toxin on the genome behind a the promoter of stress factor that response to nutrition limitation. Because our sticker is a closed system there is an x amount of available nutrients. After the Food Warden bacterium is activated it will germinate and response to any rotted meat volatiles, providing the user with the answer about the freshness of the meat, and then the growth of the bacteria will continue. The growth will continue until limiting factors present themselves, one of these being the limitation of nutrients. At this 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 pigment that is toxic for Bacillus. After the production of the pigment the user knows that the meat has started to spoil and subsequently the cells are automatically killed due to the pigment. However, when the pigment is not produced, in the case of fresh meat, this might be a drawback because the cells can continue to live.

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

Besides the internal kill switch we also thought about alternative solution to kill the bacteria. One of these ideas was to incorporate a third compartment inside the sticker containing a antimicrobial substance, after use the user breaks this compartment thereby mixing the desinfectant with the cells, resulting 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.

A last idea was to microwave the sticker after use. The wave will kill the bacteria within an certain amount of time. However we did not test this solution. We need to find out the minimal time needed to kill all the bacteria and at the same time prevent the melting of the plastic.