A multiphase flow model of calcium induced morphology changes in true slime mold

The true slime mold Physarum polycephalum is a single cell organism reaching up to meters in size. The cytoplasm shows periodic shuttle streaming through a network of tubular structures attaining velocities up to 1 mm/s. The motion is driven by the periodic contraction of an actin-myosin gel that is regulated by a calcium oscillation.

When the organism is small (< 100 microns) no streaming is observed, but as it gets larger regular rhythmic steaming suddenly emerges. We present a mechanochemical multifluid model which is used to explore how the sensitivity to changes in calcium concentration is related to the stability of the sol/gel mixture. Stability of the homogeneous mixture is explored analytically in one-dimension, and computational results are presented for higher dimensions. The model demonstrates that as the organism grows, a calcium-induced spatial instability occurs which may be responsible for the initiation of streaming.

The overall goal of this work is to understand the interplay between chemistry and fluid mechanics which is necessary to transmit chemical signals and organize structures over very large distances. In addition to streaming, some other problems related to spatial organization of structure will be discussed.