Protists, eukaryotic unicellular organisms, play a crucial role in aquatic microbial food webs. Phagotrophic protists or protozoa use phagocytosis as a pathway to bring nutrient particles to the cell. They are either fully dependent on particulate food as heterotrophs or, as mixotrophs, combine photosynthesis with phagocytosis.

Recent advancements in research methodologies, including electron and optical microscopy, image analysis, flow cytometry, and "omics" technologies, have significantly enhanced our understanding of protistan phagocytosis and its implications in aquatic microbiomes. However, there remain substantial gaps in our knowledge, particularly concerning the complexity of protistan interactions within aquatic ecosystems and their broader ecological and biomedical implications

This Research Topic welcomes a variety of article types including Original Research, Review, Mini Review, Perspective and Opinion to provide a comprehensive exploration of phagotrophic protists. Among multiple aspects of unicellular phagocytosis, we welcome contributions focusing on the following under-explored aspects to deepen our understanding:

• Complexity of protistan predation in aquatic food webs such as: utilization of bacterial biofilms, interactions with animals, consequences of food selection, and role in biofilm pathogenicity.

• Interactions between bacteria and phagotrophic protists including bacteria ingested by free-living amoebae and the symbiotic or parasitic relationships that may emerge. Examples include ciliates stimulating the growth of their prey through a feedback mechanism.

• Similarity of phagocytosis between small freshwater, or soil, amoebae and phagotrophic lymphocytes, such as neutrophils and macrophages. Understanding the kinetics of feeding, ingestion, and digestion in relation to growth rates of free-living cells not only sheds light on health-related mechanisms but also offers insights into the evolutionary strategies governing cellular control.

This Research Topic was coordinated and developed by Dr. Milos Legner, an independent researcher and microbial ecologist with extensive experience in the biomedical field.

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Protistan Phagotrophy and the Far-reaching Implications

Topic Coordinator