Boundary behaviours of Leishmania mexicana: a hydrodynamic simulation study

TL;DR

This study uses hydrodynamic simulations to investigate how Leishmania mexicana promastigotes interact with surfaces, revealing that simple hydrodynamics and morphology influence their boundary behaviors and attachment mechanisms.

Contribution

It introduces a computational model of Leishmania motility near surfaces, highlighting the role of hydrodynamics and morphology in boundary interactions and attachment.

Findings

No stable boundary motility observed near passive surfaces.

Surface detachment may result from hydrodynamics and morphology.

Hydrodynamic mechanism may explain tip-first attachment to midgut epithelium.

Abstract

It is well established that the parasites of the genus Leishmania exhibit complex surface interactions with the sandfly vector midgut epithelium, but no prior study has considered the details of their hydrodynamics. Here, the boundary behaviours of motile Leishmania mexicana promastigotes are explored in a computational study using the boundary element method, with a model flagellar beating pattern that has been identified from digital videomicroscopy. In particular a simple flagellar kinematics is observed and quantified using image processing and mode identification techniques, suggesting a simple mechanical driver for the Leishmania beat. Phase plane analysis and long-time simulation of a range of Leishmania swimming scenarios demonstrate an absence of stable boundary motility for an idealised model promastigote near passive or repulsive surfaces, with behaviours ranging from boundary capture to deflection into the bulk. Indeed, the inclusion of a repulsive surface force results in the deflection of all surface-bound promastigotes, suggesting that the documented surface detachment of infective metacyclic promastigotes may be the result of morphological adaptation and simple hydrodynamics. Further, simulation elucidates a remarkable morphology-dependent hydrodynamic mechanism of boundary approach, hypothesised to be the cause of the well-established phenomenon of tip-first epithelial attachment of Leishmania promastigotes to the sandfly vector midgut.