The cytoplasm is a crowded and dynamic fluid within which cellular building blocks such as mRNA, proteins, or organelles, undergo transport and mixing. Although small things like proteins can eventually mix through diffusion, the high viscosity of cytoplasm means that it should be difficult to obtain significant mixing for structures in the size range of organelles. In large amoeboid cells, the cytoplasm undergoes active streaming coupled to cell motility, but this streaming is laminar flow which is not effective for mixing. In this work, we used a combination of live cell tracking of injected beads and computational analysis of motion and mixing to discover that the giant amoeba Chaos carolinensis overcomes these limitations using a novel cytoplasmic gel state capture and release strategy that facilitates the efficient mixing of cytoplasm. While it was previously thought that the amoeba solution to gel state transitions only occurs at the trailing and leading edge of the cell, our work indicates that these transitions occur frequently throughout the mid-cell region, driving the cytoplasmic mixing of beads and organelles. These results indicate that amoeba reaches a stable mixed state during motility in as little as one cytoplasmic stream/flow cycle, effectively making it a Bernoulli mixing system and thus one of the fastest possible known intracellular mixers.
Diaz et al. (Sun,) studied this question.