A new encryption method, “steganography by printed arrays of microbes (SPAM),” uses a collection of Escherichia coli strains modified with fluorescent proteins that glow in a range of seven colors.

“You can think of all sorts of secret spy applications,” says David Walt, a chemist at Tufts University, who led the research.

Ref.: Manuel A. Palacios, et al., InfoBiology by printed arrays of microorganism colonies for timed and on-demand release of messages, PNAS, September 2011 [doi:10.1073/pnas.1109554108]