I Safety Design
Safety is always the first thing we concern about. In order to make the two enzymes (DEX and FruA) function on teeth, we want the safest media to contain the enzymes and transport them into the oral cavity. After weighing the safety risk of the human body and environment, we finally choose yogurt as the container of our product. Since the yogurt would be directly taken into the human body as the users drink it, we need to judge the safety level of our product extremely carefully.
II Human Body
Considering the potential risk of our product on the human body, we make three special designs to ensure our product being safely edible.
Firstly, we choose Lactococcus. lactis as the bacteria to make yogurt. As one of the bacterium people use extensively in the production buttermilk and cheese, such as Cheddar and Colby, L. lactis is safe enough to be utilized in our project as the generator of yogurt.
Secondly, our selection marker is lacF, which can be used on harmless plasmid vector, expressing protein without antibiotic resistance. This means no additional side effect would be presented after people drinking our product.
What’s more, the two enzymes we choose, DEX and FruA, which can decompose sucrose and dextran, are both edible. Thus, the main functional part of the whole design can also be taken into the human body without danger, ensuring the safety of our product.
When the human body takes the yogurt into the digestive system, it is almost unavoidable that some of the excreta would be released into the environment. Particularly, the genetically-modified bacterias have a huge potential risk of influencing the environment in an unpredictable way. In order to minimize the effect, we design a self-killing system for those bacteria in our product.
The working mechanism of the self-killing system is inducing two enzymes to hydrolyze cytomembrane and cytoderm, killing L. lactis and releasing particular enzymes in the cell. This process is achieved by an inductor called Nisin. As shown above, nisRK serves as corepressor while holin and lysin are hydrolytic enzymes which can split cytomembrane and cytoderm of L. lactis, ensuring no genomic modified bacteria being released to the environment.
As an antibacterial peptide produced by L. lactis, Nisin is commonly used in food industry to preserve cheese, meats, beverages, etc. by suppressing pathogenic bacteria. We don’t need to concern too much about the potential risk to human body of this antibacterial peptide because it is used as a food addictive in everyday life. While the safety of Nisin is justified by empirical experience, it has no inhibitory effect on L. Lactis because a series of immunogene from L. lactis is used to resist the effect of nisin. Judging from this aspect, the inductor of the self-killing system is safe as well.
In conclusion, we design our product in a way that is safe for human body while at the same time having little negative influence on environment as the self-killing system eliminate the further connection between excretory bacterium and the external environment.