Bacteria send signals from beyond the grave

Swarming is a type of collective motion in bacteria. But it turns out that moving isn’t the only thing swarming bacteria do together. They also send signals that turn on antibiotic resistance mechanisms that are specific to swarming bacteria. The surprising thing is that the bacteria releasing the signals are dead. Souvik Bhattacharyya, David M. Walker, and Rasika M. Harshey of the University of Texas at Austin have now figured out how dead swarming Escherichia coli release a protein called AcrA when they die (Nat. Commun. 2020, DOI: 10.1038/s41467-020-17709-0). This protein is part of the AcrAB-TolC efflux pump, one of many TolC pumps that the bacteria use to pump drugs out of their cells. The AcrA from dead cells interacts with TolC on the surface of live E. coli and stimulates several defense mechanisms, including breakdown of reactive oxygen species and increased expression of TolC and other efflux pumps. The researchers find that other species of swarming bacteria similarly produce species-specific “necrosignals.” The researchers suggest that such behavior is a form of altruism in which the death of some bacteria can increase the overall survival of the swarm.