Metal transportation
From 2007.igem.org
- In this project our aim is to transport specific metal ions from a specific location to another on the surface of engineered bacterial cells. In other words, to use cells as metal carriers.
We didn't want the metal ions to be uptaken by the cells since we want to transport specific metal ions (eg. radioactive ones) so we focused on putting metal-binding domains on the surface of the bacterial cells. This can be done by adding short metal-binding domains to bacterial constitutively expressed transmembrane proteins such as LamB or OmpC.
Ref: Engineering the Escherichia coli outer membrane protein OmpC for metal bioadsorption, Norberto Cruz, Sylvie Le Borgne, Georgina Hern´andez-Ch´avez, Guillermo Gosset, Fernando Valle & Francisco Bolivar, 2000, Biotechnology Letters, 22: 623–629
For the metal transportation to occur the cells should adsorp metal ions at a specific location and release them at another specific location. In order to achieve this we planned to use the pH dependence of the metal-binding domains' affinity for metals.
We need at least a semi-solid medium for bacterial cell movement. Thus, we cannot use a constant pH gradient in the medium due to diffusion.
We decided to use the bacteriorhodopsin/proteprhodopsin molecule, which transports protons into the cells when exposed to light at a specific wavelenght. We think that it will create a pH decrease at the surface of the cells if the cells are illuminated with a specific wavelength of light. This sudden pH decrease will cause the metal-binding domains to release the metals that they have previously bound. So the location where we want the cells to release the metal ions should be illuminated with a specific wavelength.
We planned to use phototaxis in order to make the cells move from metal ion-rich area to our desired location for release We did not want to use chemotaxis because of the limitations caused by diffusion. Although, E.coli lacks a phototaxis mechanism, but have a chemotaxis; fortunately, these two taxis mechainsm have similar molecular mechanisms except for the receptor parts. Thus, E.coli cells can be engineered to give taxis responses to light.
Ref: An Archaeal Photosignal-Transducing Module Mediates Phototaxis in Escherichia coli, KWANG-HWAN JUNG, ELENA N. SPUDICH, VISHWA D. TRIVEDI, AND JOHN L. SPUDICH, 2001, Journal of Bacteriology, Vol. 183, No. 21, p. 6365–6371
As a result we will have a medium in which metal uptake and release locations and also the path are illumintated by lights at specific wavelenghts. We could imagine that the E. coli cells will act as trucks carrying cargo (metal ions) from one house to another on a road we instantaneously build by using light.
Where can we use such a complex system: -In bioremediation, cleaning heavy metals and also nuclear remnants (There are metal binding proteins for a variety of matals, and even for uranium) -In high degree purification of metals for industrial purposes
