“The idea that a virus is detecting a molecule that bacteria use for communication — that is brand-new,” said Bassler, the Squibb Professor of Molecular Biology. “Justin found this first naturally occurring case, and then he re-engineered that virus so that he can provide any sensory input he chooses, rather than the communication molecule, and then the virus kills on demand.” Their paper will appear in the Jan. 10 issue of the journal Cell.

A virus can only ever make one decision, Bassler said: Stay in the host or kill the host. That is, either remain under the radar inside its host or activate the kill sequence that creates hundreds or thousands of offspring that burst out, killing the current host and launching themselves toward new hosts.

There’s an inherent risk in choosing the kill option: “If there are no other hosts nearby, then the virus and all its kin just died,” she said. VP882 has found a way to take the risk out of the decision. It listens for the bacteria to announce that they are in a crowd, upping the chances that when the virus kills, the released viruses immediately encounter new hosts. “It’s brilliant and insidious!” said Bassler.