Team:UC Davis/pH Sensor

=“Wiring the pH Sensor Into Our System”=

The pH Sensor
ChvG is a suspected pH sensor and histidine kinase and ChvI is its cognate response regulator (2). Together they are believed to sense extracellular pH between 5.5 to 7 and relaying this signal to regulate the expression of key virulence related genes. (2)

In our design, we used this two-component system from Agrobacterium tumefaciens, to regulate the expression of select target genes.

Possibility of Cross Talk
Bacteria have numerous related kinase/response regulated based, two component systems (5). For instance, the Agrobacterium tumefaciens genome is known to contain at least 25 two-component pathways (2).Therefore, there are possibilities of crosstalk between some genes present in E. coli that have the same mechanism as ChvI/ChvG system. In fact, there is evidence supporting that ChvI can complement a PhoB deletion in E. coli. (3) Therefore it is highly likely that there is a possibility of cross talk between our new sensory systems elements, present in E. coli. Many protein-protein interactions are not fully understood (5), which makes this project more challenging but very interesting.

=Finding an Appropriate Biological pH Sensor=

Why is There a Need for a pH Sensor?
We would like our probiotic organism to confine itself to the stomach. Since low pH is a hallmark of the stomach, it seems reasonable to assume that linking the production of a suicide gene to a dramatic increase in pH (to values found in the intestine) should allow us to sequester our organism to the stomach. There are no pH sensors available on the registry of biological parts. So, we will engineer a device to sense extracellular pH changes and design it so that it can be used to regulate the expression of any target gene in confinement by pH levels, and then add it to the registry! Finding an appropriate biological pH sensor:

We have decided to design our pH sensor by adopting one of the pH sensors of Agrobacterium tumefaciens. The ChvG/ChvI two component system of Agrobacterium is suspected to sense extracellular pH changes (2) and relay this environmental signal to numerous virulence related promoters (2).

More on ChvG

Once our pH sensor is built, we will need to test its behavior in response to changes to external pH. For more information go to assay for pH sensor


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