Genetically engineered cells and microorganisms are provided for preventing or ameliorating diseases through genetically engineered quorum signaling. Therapeutic methods for using the cells and microorganisms to prevent or ameliorate diseases are also provided. The genetically engineered cells or microorganisms can be engineered to express a signal and used to interrupt the signaling-dependent virulence of an invading pathogen. The cells or microorganisms can be used to provide signal-dependent expression of a desirable gene in order to interrupt, prevent, and/or ameliorate a disease of mammals, such as parasitic diseases, infectious diseases, autoimmune diseases and genetic disorders.