Scientists have made Pac-Man using  paramecium, in which movement of the microorganisms is controlled with a joystick while a digital microscope relays images to a computer screen.  The joystick is connected to a controller that controls the polarity of a mild electrical field applied across the fluid chamber, which influences the direction in which the paramecia move. 

Read more here:

http://www.newscientist.com/blogs/nstv/2011/01/play-pacman-pinball-and-pong-with-a-paramecium.html