Mechanistic models, together with empirical flow measurements, show that the ‘swim’ and ‘stay’ strategies in ciliates are equally effective for nutrient transport. Image credit: Jingyi Liu and Eva Kanso (CC BY 4.0).
Microorganisms living in aquatic ecosystems often face challenges in acquiring nutrients because resources are frequently diluted or unevenly distributed. To overcome these obstacles, organisms either swim toward nutrient-rich areas or attach to surfaces and generate feeding currents that draw in nutrients. However, research has long been inconclusive on which strategy is more efficient.
These ‘swim’ or ‘stay’ strategies shape material transport through aquatic trophic systems, affecting both individual fitness and broader processes such as global biogeochemical cycles and food web dynamics. Understanding microbial behavior is therefore essential for explaining patterns observed in natural communities and for clarifying mechanisms of material transport, nutrient acquisition, and the ecological roles of microorganisms.
Liu et al. examined how well these strategies work by analysing the shapes and flow patterns of ciliates. They found that both swimming and remaining attached can be equally effective for ciliates in typical aquatic environments. By combining mechanistic modelling with data from previous studies, they demonstrated that both strategies achieve comparable transport of nutrients and waste products. These findings suggest that evolutionary pressures have shaped these behaviours in alignment with the underlying physics of fluid flow.
They also showed that distributing ciliary activity across the cell surface improved the nutrient uptake by thinning the nutrient-depletion boundary layer – the region of fluid surrounding a cell where nutrient concentrations are reduced due to consumption. A thinner boundary layer allows nutrients to diffuse more rapidly toward the organism, revealing key design principles for maximising nutrient uptake.
Overall, Liu et al. resolve a longstanding debate by demonstrating that both feeding strategies of ciliates are equally effective. Their work provides a deeper insight into the behaviour of microorganisms and highlights the interplay between evolution and fluid mechanics. Future research should explore the evolutionary, ecological, and behavioural factors influencing feeding strategies, as well as the functional advantages of optimised cilia arrangements.
