A quantitative look into microorganism hydrodynamics

Microorganisms, such as bacteria, microphytes (tiny plants such as microscopic algae), and protists (a diverse group of single cell organisms), are present in every part of the biosphere: giant plankton blooms in the oceans, protozoa in our lakes and ponds, beneficial or pathogenic bacteria in our bodies are but a few examples that we are all familiar with. The ability of microorganisms to move through fluid environments is critical to biological and ecological functions as diverse as reproduction, pathogenic infection, mixing and CO2 capture in the oceans, among many others. Our understanding of their motility mechanisms, dynamics, and interactions remains limited, however, in part owing to our lack of quantitative information about the flows they generate on the microscale. In articles published in Physical Review Letters, two different research groups present measurements of the flow fields driven by swimming microorganisms. In the first study, Knut Drescher and co-workers at the University of Cambridge, UK, describe the first detailed quantitative measurements of the time-averaged flows around two different types of model swimming microalgae: Volvox carteri and Chlamydomonas reinhardtii [1]. In the second article, Jeffrey Guasto and co-workers at Haverford College, US, also measure the flow field driven by Chlamydomonas reinhardtii, but focus on its oscillatory nature using timeresolved measurements [2]. Both studies clearly demonstrate that these flow fields are more complex than was previously believed, opening the door for new and more accurate models for the hydrodynamics of microorganismal colonies.