Cell behavior in traveling wave patterns of myxobacteria.

Cells in the early stages of starvation-induced fruiting body development migrate in a highly organized periodic pattern of equispaced accumulations that move as traveling waves. Two sets of waves are observed moving in opposite directions with the same wavelength and speed. To learn how the behavior of individual cells contributes to the wave pattern, fluorescent cells were tracked within a rippling population. These cells exhibit at least three types of organized behavior. First, most cell movement occurs along the same axis as the rippling movement. Second, there is a high degree of cell alignment parallel to the direction of rippling, as indicated by the biased movement. Third, by controlling the reversal frequency, cell movement becomes periodic in a rippling field. The periodicity of individual cells matches the period of macroscopic rippling. This last behavior is unique to a rippling population and, on the basis of Myxococcus xanthus genetic data, we conclude that this periodicity is linked to the C signal, a nondiffusible cell contact-mediated signaling molecule. When two cells moving in opposite directions meet end to end, they transmit the C signal to each other and in response reverse their gliding direction. This model of traveling waves represents a new mode of biological pattern formation that depends on cell-contact interactions rather than reaction diffusion.