Prey capture in protists utilizing microtubule filled processes and surface motility

Abstract

Surface motility, which can be visualized by the movement of live prey organisms, polystyrene microspheres or other inert particles, has been shown to occur in a wide variety of microtubule-filled extensions of the protistan cell surface, although the associated functions remain enigmatic. This article integrates an extensive but poorly known body of literature showing that surface motility, associated with microtubulefilled cell extensions such as flagella, axopodia, actinopodia, reticulopodia, and haptonema, plays a crucial role in protistan prey capture. Surface motility has been most extensively studied in Chlamydomonas where it is responsible for flagelladependent whole cell gliding motility. The force transduction machinery for gliding motility in Chlamydomonas is intraflagellar transport. Other than in Chlamydomonas, this field has not moved far beyond the descriptive to the mechanistic because of technical challenges associated with many of the protistan organisms that utilize surface motility for prey capture. The purpose of this article is to rekindle interest in the protistan systems that utilize surface motility for prey capture at a time when newly emerging molecular tools for working with protists are poised to reinvigorate a field that has been quiescent too long.

Hydrodynamics of Prey Capture and Transportation in Choanoflagellates

“…Here, a is the major and b is the minor radius of the spheroid, and C n is the specific drag coefficient for the described case. The limitation of Equations (10) and (11) is that they do not take into account the non-uniform velocity field in the vicinity of the filter or the influence of the finite size of the prey and its boundary condition-as it is either non-slip for the fixed prey or globally force and torque free for the freely moving prey. Hence, when using the Stokes law, the velocity estimate for the prey may be an overestimation.…”

“…However, as we simply wish to evaluate the order of the prey velocity, the first-order Stokes estimate is considered sufficient. Consequently, we choose to use Stokes (Equations (10) and (11)) to approximate the prey velocity from the forces on the fixed prey.…”

“…The prey velocity also depends on the shape and size of the prey, which could negate or weaken effects of increased or reduced forces on the prey. We use the Stokes law in Equations (10) and (11) to transform the simulated tangent forces on the four different prey types (Table 2) into their respective tangent velocities. We note that the force contributions from pressure and viscous forces are approximately 1:1 for all prey types during one beat cycle.…”

“…Many protists, however, take advantages of surface motility by utilizing microtubule-filled extensions to capture and handle prey particles (cf. Bloodgood [11]). Bloodgood reviewed different exam-ples of the surface motility in these protists, which always happens "on plasma membrane domains associated with microtubule cytoskeletons that vary greatly in complexity" [11].…”

“…Bloodgood reviewed different exam-ples of the surface motility in these protists, which always happens "on plasma membrane domains associated with microtubule cytoskeletons that vary greatly in complexity" [11]. Choanoflagellates, however, do not have these extensions, and it has been argued that prey transportation in choanoflagellates must have a different underlying mechanism [11]. The possibility that prey transportation in choanoflagellates relies on molecular motors, such as encasement in pseudopods, has previously been explored [12].…”