The myxobacterium Myxococcus xanthus has a life cycle that is dominated by
social behavior. During vegetative growth, cells prey on other bacteria in
large groups that have been likened to wolf packs. When faced with starvati
on, cells form a macroscopic fruiting body containing thousands of spores.
The social systems that guide fruiting body development have been examined
through the isolation of conditional developmental mutants that can be stim
ulated to develop in the presence of wild-type cells. Extracellular complem
entation is due to the transfer of soluble and cell contact-dependent inter
cellular signals. This review describes the current state of knowledge conc
erning cell-cell signaling during development.