Programmed cell death in bacteria is dependent on a system of cell-to-cell communication termed quorum sensing. Extracellular death factor (EDF) is a linear pentapeptide that communicating cells produce and release, which upon reaching a sufficient concentration activates the cell death pathway in a subset of cells. It is sensitive to extreme pH, high temperatures, and other stressful conditions. At 2.5 ng/ml, EDF has been shown to facilitate mazEF-mediated cell death, significantly reducing population size in E. coli cultures.