Revision as of 05:57, 19 September 2012 by Zhanghong (Talk | contribs)

Chez is dephosphorylase of CheY in chemotaixs pathway. Three main characteristics actuate our consideration of CheZ. First, several experiments indicate that chez can effect the movement of bacteria: Increasing levels of chez induced by arabinose can enlarge the diameter of swarming colony. Chez deletion causes cells to tumble incessantly, resulting in a nonmotile phenotype in semisolid agar. Reintroducing CheZ restores cell motility. Second, CheZ is commonly used as motility-control module in synthetic biology. Combination between the Chez and quorum sensing LuxI/R part forms stripe pattern in colony. Bacteria with Chez under the control of an atrazine binding riboswitch proves capability of atrazine chemotaxis. Chez controlled by theophylline riboswitch of upstream random sequence acts as a colony reporter for orthogenesis. Furthermore, CheZ is included in some downsteam locomotive part of bacteria phototaxis such as Halobacterium. On this basis, we decided to use CheZ to control the mobility of the bacteria.

Through rational consideration, we embark on building the circuit. Chez can only function at a high expression level, so we link CheZ with strongest RBS B0034 and a high copy plasmid. The circuit of our phototaxis part consists two plasmids containing LexA408-VVD and RecA408-cheZ, respectively. Bacteria luminated by blue light leads to repression of CheZ, resulting to lack of cell motility.

Figure 1.

Figure 1. (circuit picture)

After gathering principles and parameters of chemotaxis system, we then simulate our phototaxis system in a stochastic way to present the phototaxis mechanism of our system. With the mechanism above, we construct our simulation system as modeling shows(Details here).

Figure 2.

Figure 2. (pic modeling result).

As the modeling proves our circuit, we design several experiments to realize it. Firstly, we have to prove the function of CheZ. Two experiments are designed: the measurement of diameter of mobile(MG1655) and immobile(tran5α and ΔCheZ MG1655) bacteria and the bacteria with chez under different strength of promoter J23112,J23113,J23114, J23110, whose variant RFP are 1,21,256,844,respectively. Sceondly, plates pasted polaroid of different transmittance are used to measure the chez expression under different light strength. Thirdly, plot the bacteria in the center of the plate whose half is opaque. These experiments are expected to have different diameter of colony or oval shape of colony to show the phototaxis.

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