In a new study, researchers from the center describe how mixotrophic microorganisms make use of feeding currents to increase both prey encounter rates and the incoming flux of inorganic nutrients. They argue that virtually all heterotrophic microorganisms must have similar mechanisms.
Mixotrophy is common, if not dominant, among eukaryotic flagellates, and these organisms have to both acquire inorganic nutrients and capture particulate food. Diffusion limitation favors small cell size for nutrient acquisition, whereas large cell size facilitates prey interception due to viscosity, and so intermediately-sized mixotrophic dinoflagellates are simultaneously constrained by diffusion and viscosity. Advection may help relax both constraints.
In this paper, we use high-speed video-microscopy to describe prey interception and capture, and micro-particle image velocimetry to quantify the flow fields produced by free-swimming dinoflagellates. We provide the first complete flow fields of free-swimming interception feeders, and demonstrate the use of feeding currents.
This leads us to argue that feeding currents efficiently allow the grazer to approach small-sized prey despite viscosity.
The fluid deformation created in such feeding currents may be detected by evasive prey, but the magnitude of flow deformation varied widely between species and depends on the position of the transverse flagellum.
We also use the near-cell flow fields to calculate nutrient transport to swimming cells and find that feeding currents may enhance nutrient uptake by ≈75% compared to that by diffusion alone.
We argue that all phagotrophic microorganisms must have developed adaptations to counter viscosity in order to allow prey interception, and conclude that the flow fields created by the beating flagella in dinoflagellates are key to the success of these mixotrophic organisms.
The study is available here