The voltage output part of our project aims to mimic the signal transduction that occurs at a neural synapse.
We are engineering E.coli to create a voltage output on detection of glutamate. This imitates the creation of a postsynaptic potential in a dendrite when a neurotransmitter (such as glutamate) is present at the synapse.
The mechanism we have designed is similar to that used in the brain – relying on ion movement across the membrane, and gated ion channels.
To simplify the concept, we are only regulating and measuring the flux of potassium (K+) ions, and we are using a directly glutamate-gated K+ ion channel.
This means that on the binding of glutamate, the channels will open, allowing a K+ flux, which will change the voltage of the medium enough to be detected with a very sensitive electrode.
In order to set up a large enough K+ concentration gradient across the membrane for ions to flow down when the channels open, cells are grown in high K+ medium (100mM) and resuspended in low K+ medium.
However, E.coli also has a number of osmoregulatory systems which use relative K+ ion concentrations to control turgor. There are K+ leak channels (Kch and Kef) in the membrane, so we have chosen E.coli strains with mutations in these genes as our chassis.