The impact of selective predation of weaker individuals on the general health of prey populations is well-established in animal ecology. Analogous processes have not been considered at microbial scales despite the ubiquity of microbe-microbe interactions, such as parasitism. Here we present insights into the biotic interactions between a widespread marine thraustochytrid and a diatom from the ecologically important genus Chaetoceros. Physiological experiments show the thraustochytrid targets senescent diatom cells in a similar way to selective animal predation on weaker prey individuals. This physiology-selective targeting of ‘unhealthy’ cells appears to improve the overall health (i.e., increased photosynthetic quantum yield) of the diatom population without impacting density, providing support for ‘healthy herd’ dynamics in a protist–protist interaction, a phenomenon typically associated with animal predators and their prey. Thus, our study suggests caution against the assumption that protist–protist parasitism is always detrimental to the host population and highlights the complexity of microbial interactions.
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We thank the crew of the RV Sepia for sampling and Angela Ward and Claire Hopkins (MBA) for their guidance with isolation and culturing. We also thank Glenn Harper, Alex Strachan and the team at the Plymouth Electron Microscopy Centre (PEMC) for their assistance with SEM. We are indebted to Jingwen Pan (University of British Columbia) and Javier del Campo (Institute of Evolutionary Biology, Spain) for providing the reference sequences used in building phylogenetic trees in this study, as well as to Daniel Vaulot (Station Biologique de Roscoff) for help in interpreting the Ocean Sampling Day data. Nathan Chrismas (MBA) is also thanked for bioinformatic support.
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Laundon, D., Mock, T., Wheeler, G. et al. Healthy herds in the phytoplankton: the benefit of selective parasitism. ISME J 15, 2163–2166 (2021). https://doi.org/10.1038/s41396-021-00936-8