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 loaction. In order to achieve this we planned to use the pH dependence of the metal-binding domains for their affinity for metals.
We need at least a semi-solid media for bacterial cell movement. Thus, we cannot use a constant pH gradient in the medium due to diffusion.
We decided to use the bacteriorhodopsin molecule, which transports protons into the cells due 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 loaction that we want the cells to release the metals should be specifically illuminated with a specific wavelength.
Another point about the project is to force the bacterial cells to meve from one specific location to another. We cannot use chemotaxis due to limitations caused by diffusion. So we decided to use phototaxis. However,E.coli lacks a phototaxis mechanism but have a chemotaxis mechanism. 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
