From 2007.igem.org

1)The first state of the system, where there is a concentration of metal ions on one sideof the semi solid medium. The cells are exposed to no particular wavelength at this time. They bind metals with their metal binding domains. 2)The pink cells are those that carry metal ions on their surfaces, they are moving towards lamp 2 by phototaxis.3)Now the third lamp which will activate the bacteriorhodopsin and cause release of metal ions is switched on, so the exposed cells are releasind the metal ions.4) After metal ions are released, lamp 2 is switceh off and lamp 1 is switched on, so the cells bedin to go back to collect remaining metal ions in the original location. 5) 6)Now the cycle will start again. Because the metal binding domains are extremely sensitive to metal ions, the cells will still be able to continue collecting them, when their concentration is decreased to very low levels (even at the level of single atoms).