Formation of whirling aggregates by Labyrinthula vegetative cells

A novel form of aggregation of the vegetative cells of the colonial marine protist Labyrinthula has been analysed cinematically and induced reproducibly in vitro by addition of gelatin to the growth medium. Vegetative cells are observed to converge spirally to a center and continue to move circularly around the center with a mean angular velocity of 150 °/min, suggesting the existence of a gradient of chemoattractant. The possibility is discussed that the system of actin rails located in the slimeways in which cells move is arranged circularly to permit the observed movements.