Genetically modified yeast can sniff out explosives

What do you get if you cross a rat, a jellyfish and brewer's yeast?
Happily, the answer is not the latest genetically modified food, but a
low-cost explosives detector.

Danny
Dhanasekaran, a molecular biologist at Temple University in Philadelphia, Pennsylvania, has coaxed a simple yeast into harnessing a
rat's sense of smell to sniff the explosive trinitrotoluene (TNT), a
primary ingredient in many explosive devices. When it finds it, the
yeast emits a warning using the jellyfish's ability to softly glow.

Funded
by the Pentagon's Defence Advanced Research Projects Agency, Dhanasekaran hopes to create a lightweight detector that is much
cheaper than today's precision-engineered electronic noses. The yeast
sensor could one day be installed at ports and railway stations, or
built into a PDA-size device, to warn of the presence of explosives, or
chemical or biological weapons.

Dhanasekaran's
team first cloned the genes for smell receptor proteins in rats. There
are around 500 such proteins, and different odour molecules latch onto each one, producing enzymes that activate electrical signal pathways to
the brain. Brewer's yeast, Saccharomyces cerevisiae, uses the
same type of protein receptors and signalling to detect pheromones
during reproduction, so the researchers decided to use the yeast as
their communications channel, and shuttled the cloned rat genes into
its genome. "Yeast can be tricked into using the rat olfactory signals
very easily," says Dhanasekaran.

Then,
to alert users that the yeast has detected an explosive substance, they inserted a jellyfish gene for a green fluorescent protein, visible
under ultraviolet light, which is produced when the olfactory pathway
is activated (Nature Chemical Biology, DOI: 10.1038/nchembio882).