Do microscopic organisms feel turbulent flows?
Microscopic organisms in aquatic environments are continuously exposed to a variety of physical and chemical conditions. Traditionally, it is accepted that due to their small size the physiology of microscopic organisms is not affected by the moving fluid at their scale. In this study, we demonstrate that the small-scale turbulence significantly modulates algal and bacterial nutrient uptake and growth in comparison to still-water control. The rate of energy dissipation emerges as a physically based scaling parameter integrating turbulence across a range of scales and microscopic organism responses at the cell level. Microbiological laboratory tests and bioassays do not consider fluid motion as an important variable in quantifying the physiological responses of microorganisms. A conceptual model of how to integrate the fluid motion in Monod-type kinetics is proposed. We anticipate our findings will encourage researchers to reconsider the laboratory protocols and modeling procedures in the analysis of microorganism physiological responses to changing physical and chemical environments by integrating the effect of turbulence.