Programmed Cell Death in Unicellular Versus Multicellular Organisms

Programmed cell death (self-induced) is intrinsic to all cellular life forms, in-cluding unicellular organisms. However, cell death research has focused on animal models to understand cancer, degenerative disorders, and develop-mental processes. Recently delineated suicidal death mechanisms in bacteria and fungi have revealed ancient origins of animal cell death that are inter-twined with immune mechanisms, allaying earlier doubts that self-inflicted cell death pathways exist in microorganisms. Approximately 20 mammalian death pathways have been partially characterized over the last 35 years. By contrast, more than 100 death mechanisms have been identified in bacte-ria and a few fungi in recent years. However, cell death is nearly unstudied in most human pathogenic microbes that cause major public health bur-dens. Here, we consider how the current understanding of programmed cell death arose through animal studies and how recently uncovered micro-bial cell death mechanisms in fungi and bacteria resemble and differ from mechanisms of mammalian cell death.