University of Texas 2006

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The UT Austin team is:

  • Aaron Chevalier
  • Eric Davidson
  • [http://openwetware.org/wiki/User:Jeff_Tabor Jeff Tabor]
  • Laura Lavery
  • Matt Levy
  • [http://www.mine-control.com/ Zack Booth Simpson]
  • Bryan Kaehr


Advisors:

  • [http://ellingtonlab.org/ Andy Ellington]
  • [http://polaris.icmb.utexas.edu/home.html Edward Marcotte]


Contents

Previous work: Bacterial Photography

In the dark, OmpR is phosphorylated, LacZ is expressed, and a sugar (S-Gal) in the medium is cleaved to leave a black chemical deposit. This signal transduction cascade is repressed in the presence of red light
Chucky D. Bacterial photo: Aaron Chevalier















For the 2004 Synthetic Biology Competition, our joint UT-Austin/UCSF team designed a genetically encoded edge detection device. In our system, a community of genetically identical E.coli would function as a massively parallel computer capable of calculating the light/dark boundary of an arbitrary two-dimensional image.

An obvious hurdle in the implementation of this system was genetically encoding light detection in the naturally blind E.coli. To accomplish this, we used a synthetic part engineered in the Voigt lab. This part, Cph8, ([http://parts2.mit.edu/r/parts/partsdb/view.cgi?part_id=5302 I15010]) is an engineered fusion between a cyanobacterial light sensing phytochrome (Cph1) and an E.coli transmembrane histidine kinase, (EnvZ). 660nm light causes an isomerization in the Cph1 domain of the chimera which inactivates the histidine kinase acitity of EnvZ. When EnvZ is inhibited, a phosphorelay cascade which activates transcription from the OmpC promoter [http://parts2.mit.edu/r/parts/partsdb/view.cgi?part_id=3910 R0082]) and inhibits transcription from the OmpF promoter ([http://parts2.mit.edu/r/parts/partsdb/view.cgi?part_id=3915 R0084]). We then demonstrated that when this system is expressed in E.coli, it is possible to transform each cell on an agar surface into a decision making pixel capable of reporting whether it is in the light or dark. The community of cells is therefore capable of genetically reproducing a light image.


Current work: Edge detector

This was the first step in engineering the edge detector. We have now connected the light-responsive circuitry to the remainder of the edge detection circuit ([http://partsregistry.org/Part:BBa_I15022 I15022]) the schematic and operation of which are shown in the figures below.
Edge Detector Circuit. The light sensing machinery from above has been black-boxed and the edge detection circuitry has been added downstream. Red light represses the expression of 2 genes; a biosynthetic gene for a membrane diffusible quorum sensing activator (AHL), and a dominant transcriptional repressor (cI).


(Top) Micro-scale edge detection. (Bottom) Macro-scale edge detection. An image is projected onto an agar plate of E.coli expressing the circuitry shown to the left. Cells residing in dark areas express AHL but are dominantly repressed by CI. Illuminated cells express neither AHL nor cI. If they neighbor a dark area, they will be activated by locally diffusing AHL. In this way, only cells at the light dark boundary express a reporter, and the edge is detected.



















Favorite Parts

  • [http://partsregistry.org/Part:BBa_I15008 I15008]
  • [http://partsregistry.org/Part:BBa_I15009 I15009]
  • [http://partsregistry.org/Part:BBa_I15010 I15010]
  • [http://partsregistry.org/Part:BBa_I15022 I15022]

Light Controlled Chemotaxis

Photopolymerization

Links

If you'd like to take your own pictures, check out the page on [http://openwetware.org/wiki/LightCannon how to build a light cannon]
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