Idea to put the criticality detector into practice
Our criticality detector can be use to control doses of some strong medicine precisely by the impulse signals produced by it. To prove this property creatively, we construct a antimicrobial peptide producing circuit relating to dental caries prevention and homeostasis maintenance.
To be specific, when the concentration of Streptococcus mutans increase to a certain level, the criticality detector can activate the expression of targeted antimicrobial peptide to inhibit the growth of S.mutans, controlling its population in oral cavity under a healthy level.
Relationship with the criticality detector
There is a large microbial population living in our oral environment playing a major role in our fine body condition undoubtedly. However a big part of that population, the Streptococcus mutans ,would be the foundation stone of the biofilm causing tooth decay when its population size loses control. S.mutans is a kind of gram positive pathogen living in our oral cavity. It can colonize on the surface of tooth and produce acidic metabolites which can destroy tooth enamel. It can also create a special low pH micro-environment to help other oral pathogens to colonize on tooth. The growth of these pathogens as well as the metabolites they produce can gradually cause the formation of dental caries. Therefore the population of the S.mutans needs to stay in a heathy range,which means a strict control of the dose of the medicine targeting on the S.mutans. And our criticality detector can act as a dose controller perfectly by detect the pH in the micro-environment around the S.mutans population, for the pH implies the size of its population.
How to control the population of S.mutans
Antimicrobial peptides are recently regarded as a promising choice to kill microbes due to their strong microbicidal effects and their unlikeliness of triggering resistance in microorganisms. Since there are also various kinds of probiotics living in our mouth besides oral pathogens, and since antimicrobial peptides have effect on general kinds of microorganisms, it’s more wise to modify the antimicrobial peptide into a targeted one by adding a S.mutans targeted sequence on the N-terminal, so that only S.mutans can be killed. Thus we design two fused peptides, CAP-glyglygly-Bac8c and CAP-glyglygly-APP2, to targetedly inhibit the growth of S.mutans in oral cavity, where CAP is an optimized peptide that can specifically bind to the comD receptor on the surface of S.mutans, while Bac8c and APP2 are two kinds of peptides that assume strong bactericidal effect in acidic environment.
How to construct the antimicrobial peptide expression circuit
We first fuse CAP and Bac8c(or APP2) with linker “-glyglygly-” to construct targeted antimicrobial peptides. Then in order to prove their function, we express them in Pet28a with the induction of IPTG, and observe their bactericidal effect on E.coli and S.mutans to see if they have targeted effect. And finally we add criticality detector circuit on the upstream of antimicrobial peptide expression gene to control its expression, and use acid sensitive promoter AsR as the input signal sensor of criticality detector to complete the whole system.
How does the whole system work
When the concentration of S.mutans in mouth increases, the pH of the micro-environment decreases as well, and reaching to certain level it will activate promoter AsR and induce the reaction downstream in different intensity. The signal intensity will be processed by our criticality detector and an final output signal containing the information whether the antimicrobial peptide gene should or should not be expressed will transfer to the peptide expression circuit to control the expression of antimicrobial peptide. Only when the concentration of S.mutans reaches certain level, can the peptide expression circuit be activated, so that the targeted antimicrobial peptide can inhibit the growth of S.mutans, reducing its population to a lower and healthy level.
