Microswimming as a mechanism for mitochondrial wiggling

In many plant cells, there are two types of mitochondrial motion: directed and wiggling. While the former is mediated by F-actin and microtubules, the latter is not. The fact that mitochondria migrate via wiggling suggests the existence of other mechanisms of motion aside from those related to the cytoskeleton and protein motors. In this work, it is assumed that wiggling mitochondria are active Brownian particles, self-propelled bodies whose motion at low Reynolds number is affected by noise. The proposed mechanism of motion is microswimming, where a wiggling mitochondrion is driven by a cycle of shape changes resembling a peristaltic wave travelling along its body. The peristaltic wave is modelled on a two-sphere swimmer under the far-field approximation, yielding expressions for the kinetic and dynamic variables involved, as well as for the factors determining its interaction with chloroplasts. The calculations show that the microswimmer can reach reported speeds with small size deformations and explain the observed high percentage of wiggling mitochondria captured by chloroplasts. Using the hydrodynamic results enables the application of a theoretical probabilistic model, including active and passive noise, which fits well with experimental results on speed distribution and trajectories of wiggling mitochondria. Taken together, the results explain the main mitochondrial wiggling characteristics observed in experiments, thus suggesting the feasibility of microswimming as a mechanism for mitochondrial wiggling.