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Purpose

We are going to use the “control part” to control the number of Streptococcus mutans (S. mutans). When the number of S. mutans exceeds the threshold of causing cavities, the circuit will be activated, killing the excess S.mutans.

Background

It is said that the number of S. mutans is highly related to the outbreak of cavities. Therefore, controlling the number of S. mutans has been our prime priority. To reach our purpose, we need to detect the number of S. mutans, find out the threshold of causing cavities, and finally, kill the S. mutans. These three main designs of the first C, “control”, will be explain in the following words.

First of all, we need to detect the number of S. mutans. Over the years, it has been found that the competence stimulating peptide, CSP, a quorum sensing chemical, will be released in every competence S. mutans. Thus, we can detect the number of S.mutans by detecting the amount of CSP.

In S.mutans, the CSP will bind to the membrane receptor, “comD”, thereby phosphorylated the response regulator, “comE”. The phosphorylated comE will activate numerous vital biological mechanisms in Streptococcus mutans, for example, biofilm formation, mutacin release. Through all mechanisms involved with CSP, it is found that the promoter of gene “nlmC”( non-lantibiotic mutacin C) in S.mutans have a better performance under the stimulation of CSP. As a result, we decide to use this promoter in our design.

Secondly, we need to found out the threshold that causes cavities. In this part, we will use different kinds and numbers of terminators, with different leakage rate, to create the threshold. Moreover, we will combine both wet lab and modeling to decide which design is better.

Thirdly, we need to kill the S. mutans when the number of S. mutans exceeds the threshold. To fulfill our goal, we decided to incorporate our circuit into Streptococcus phage M102, which is highly specific to S. mutans, thereby control the lysis genes in phage M102.

Design

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In our circuit, we incorporate nlmC promoter and different combination of terminator. When the number of S. mutans exceed the threshold, the first “C” , control mechanism will activate the lysis genes of phage M102. Thus, control the number of S. mutans.

Result

Reference

1. Kreth, J., Hung, D. C. I., Merritt, J., Perry, J., Zhu, L., Goodman, S. D., Cvitkovitch, D. G., ... Qi, F. (January 01, 2007). The response regulator ComE in Streptococcus mutans functions both as a transcription activator of mutacin production and repressor of CSP biosynthesis. Microbiology Reading-, 153, 1799-1807.
2. Hung, D. C. I., Downey, J. S., Ayala, E. A., Kreth, J., Mair, R., Senadheera, D. B., Qi, F., ... Goodman, S. D. (June 28, 2011). Characterization of DNA Binding Sites of the ComE Response Regulator from Streptococcus mutans. Journal of Bacteriology, 193, 14, 3642-3652.
3. Liu, T., Xue, S., Cai, W., Liu, X., Liu, X., Zheng, R., Luo, H., ... Qi, W. (March 22, 2014). ComCED signal loop precisely regulates nlmC expression in Streptococcus mutans. Annals of Microbiology, 64, 1, 31-38.
4. van der Ploeg, J R. (2007). Genome sequence of Streptococcus mutans bacteriophage M102. Wiley-Blackwell.