Discussion

Title: High speed, three-dimensional imaging to inform biophysical modelling in parasitology
L.G. Wilson 2, R.C. Findlay 1,2, P.B. Walrad 1 1. York Biomedical Research Institute, Department of Biology, University of York, York, UK 2. Department of Physics, University of York, York, UK.
The interactions between physics and biology have been a rich seam of scientific advances. Cellular motility is a paradigm for these interactions. Motility is an ancient eukaryotic trait, ubiquitous across phyla with roles in predator avoidance, resource access, and competition. Flagellar motility is seen in various parasitic protozoans, and morphological changes in flagella during the parasite life cycle have been observed. We have developed a unique implementation of holographic microscopy to image swimming cells of various parasites, including Leishmania mexicana and Plasmodium berghei, in three dimensions and at rates up to 1,000 volumes per second. These measurements give insight into the relationship between flagellar structure and motility, and phenotypic variation, through quantitative data on the reaction of individual cells to an external stimulus. Among our findings, we have seen that the human-infective (metacyclic promastigote) forms of L. mexicana display ‘run and tumble’ behaviour in the absence of stimulus, reminiscent of bacterial motion, and that they specifically modify swimming direction and speed to target host immune cells in response to a macrophage-derived stimulus. Non-infective (procyclic promastigote) L. mexicana cells swim more slowly, along meandering helical paths.