KINEMATIC ANALYSIS OF TOXOPLASMA-GONDII MOTILITY

Toxoplasma gondii tachyzoites execute a complex and little understood combination of rapid movements to reach and penetrate human or other a nimal cells. In the present study, computer-assisted simulation was us ed to quantitatively analyze the motility of these parasites in three- dimensional space with spatial and temporal resolutions in the microme ter and subsecond ranges. A digital model based on electron-micrograph s of a serially sectioned tachyzoite was animated according to a video micrographed sequence of a characteristic repetitive movement. Keyfram e animation defined over 150 frames by a total of 36 kinematic paramet ers for specific motions, of both the whole model and particular domai ns, resulted in a real-time life-like simulation of the videorecorded tachyzoite movement. The kinematic values indicate that a full revolut ion of the model is composed of three half-turns accomplished in nearl y 5 s with two phases: a relatively slow 180 degrees tilting with rega rd to the substratum plane, followed by fast (over 200 degrees/s) spin ning almost simultaneous with pivoting around the posterior end, each clockwise and for about 180 degrees. Maximal flexing of the body, as w ell as bowing and retraction of its anterior end, occur at midway duri ng the tilting phase. An estimated 70 degrees clockwise torsion of the body seems to precede the spinning-pivoting phase. The results sugges t the operation of two basic forces in the motility of T. gondii tachy zoites: (1) a clockwise torque that causes torsion, spinning, and pivo ting; and (2) a longitudinal pull that contracts, bends and tilts the parasite. We discuss the possibility that both of these forces might r esult from the action of an actin-myosin system enveloping the twisted framework of microtubules characteristic of these organisms. (C) 1996 Wiley-Liss, Inc.