We present a fast, high-throughput method for characterizing the motility of microorganisms in 3D based on standard imaging microscopy. Instead of tracking individual cells, we analyse the spatio-temporal fluctuations of the intensity in the sample from time-lapse images and obtain the intermediate scattering function (ISF) of the system. We demonstrate our method on two different types of microorganisms: bacteria, both smooth swimming (run only) and wild type (run and tumble) Escherichia coli, and the bi-flagellate alga Chlamydomonas reinhardtii. We validate the methodology using computer simulations and particle tracking. From the ISF, we are able to extract (i) for E. coli: the swimming speed distribution, the fraction of motile cells and the diffusivity, and (ii) for C. reinhardtii: the swimming speed distribution, the amplitude and frequency of the oscillatory dynamics. In both cases, the motility parameters are averaged over \approx 10^4 cells and obtained in a few minutes.
@article{arxiv.1202.1702,
title = {Differential Dynamic Microscopy: a High-Throughput Method for Characterizing the Motility of Microorganism},
author = {Vincent A. Martinez and Rut Besseling and Ottavio A. Croze and Julien Tailleur and Mathias Reufer and Jana Schwarz-Linek and Laurence G. Wilson and Martin A. Bees and Wilson C. K. Poon},
journal= {arXiv preprint arXiv:1202.1702},
year = {2012}
}