Model

In our case, secret information is stored in spy yeast, and if the spy yeast is intercepted, killer yeast can secrete alpha factors to induce cell apoptosis leading to the death of spy yeast. Therefore, the time of apoptosis induction, or the time from interception to spy yeast self-destruction, is an essential part of the security of stored information. The level of security is an important criterion to evaluate the quality of our encryption system.

The time of spy yeast death induced by killer yeast is directly dependent on the expression efficiency of the proapoptotic gene, Bax, which has been engineeringly integrated into the spy yeast genome by us. In our case, the expression efficiency of Bax gene is relevant to the promoter strengthen of the Fig2c promoter. Therefore, we first analyzed the parameters of Fig2c promoter-mediated transcription. Based on the experimental procedure, we predicted that Fig2c promoter-mediated transcription is mainly proportional to the initial dosage of the spy yeast, killer yeast, and alpha factor secreted by killer yeast. To test our prediction, we conducted the partial correlation analysis. Secondly, with induced apoptosis of the spy yeast, the percentage of killer yeast would increase, while the percentage of spy yeast would decrease in the cocultured yeast population. This phenomenon could be depicted that the killer yeast preyed on the spy yeast. Therefore, we improved the initial predator-prey model and established a killing model. Using this new model, we can estimate the time of information destruction with different initial ratios between the killer yeast and spy yeast, and verify the security levels of information storage using our biological encryption system.