How to Track Protists in Three Dimensions

TL;DR

This paper introduces an advanced 3D tracking system for swimming microorganisms, enabling detailed study of their motility, phototaxis, and hydrodynamic interactions with minimal environmental interference.

Contribution

The authors develop a synchronized dual-camera microscopy setup with specialized illumination to accurately track microorganisms in three dimensions without surface effects or convective disturbances.

Findings

Successful 3D tracking of microorganisms from 10 to 1000 microns

Detailed analysis of phototactic trajectories in 3D

Investigation of hydrodynamic interactions near surfaces

Abstract

We present an apparatus optimized for tracking swimming microorganisms in the size range 10-1000 microns, in three dimensions (3D), far from surfaces, and with negligible background convective fluid motion. CCD cameras attached to two long working distance microscopes synchronously image the sample from two perpendicular directions, with narrowband dark-field or bright-field illumination chosen to avoid triggering a phototactic response. The images from the two cameras can be combined to yield 3D tracks of the organism. Using additional, highly directional broad-spectrum illumination with millisecond timing control the phototactic trajectories in 3D of organisms ranging from Chlamydomonas to Volvox can be studied in detail. Surface-mediated hydrodynamic interactions can also be investigated without convective interference. Minimal modifications to the apparatus allow for studies of chemotaxis and other taxes.