Team:SDU-Denmark/project-t

Theory

In this section we will review the theory behind our approach to establishing a flow through a microtube.

Phototaxis

We want to be able to control, switching on and off, our flow through a remote signal. Our preferred signal is light, since light does not have any effect on the rest of the system and only interacts with the membrane receptor in E.Coli. This means that the probability of unwanted side effects is minimized, since there are no excess interactions between the signal and its target environment.

The type of light that we will use for this is bluelight, which functions as a repellent in our case. This will make the bacteria want to get away from the light source which in turn results in an increased tumbling frequency, why will be explained a little further down this text. Since we chose E.Coli as our model organism and wanted to use a light signal, we would have to increase it's sensitivity to bluelight, which naturally is very, very small. Thorugh research we found out that teh Halobacterium Salinarum has a very well researched phototaxis mechanism, where the individual membrain domais role in thr process had been solved AND transferred to E.Coli. Which means that we would have to pick up on that research and create this mechanism as biobricks.

The following model shows the way we want to couple the phototaxis pathway to E.Coli's natural chemotaxis pathway. This is almost identical to the phototaxis pathway in Halobacteria except that the HtrII is directly coupled to CheA, so that there is no Tsr involved.

The way the halobacterial pathway works is that the photonreceptor is a protein called sensory rhodopsin II, which absorbs the blue light and in response changes it's conformation. HtrII is just a transducer and signals this to CheA, which in turn gets phosphorylated and afterwards passes the phosphate group on to CheB. Phosphorylated CheB binds to the flagellar motor switch, so that the flagella start rotating clockwise, which induces the tumbling motility pattern. The more CheY gets phosphorylated the higher the tumbling frequency will be.

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