They contribute significantly to microbial ecology, soil fertility and water quality. They also have an enormous impact on animal and human health, with many species known as emerging pathogens. Protists interact with other microbes (viruses, archaea, bacteria and fungi) through predatory, mutualistic or symbiotic relationships. This makes the study of protists (protistology) an important node in the different fields of biology, including ecology, infectious diseases and evolution. Ecology. Protists have been isolated from diverse habitats, including extreme environments, such as polar regions, deserts or deep-sea ocean vents. Advances in protistology reveal new species and ecological interactions with other organisms. Their key roles in environmental niches highlight their importance in influencing environmental health. Infectious disease. Many human and animal obligate and opportunistic parasites are protists. They use different routes to transmit infections, e.g. through vectors ( Plasmodium, Leishmania, Trypanosoma) or the oral-faecal route ( Cryptosporidium , Toxoplasma oocysts, Eimeria, Entamoeba , Giardia ). A common challenge with all protist pathogens is the tremendous difficulty in treating and preventing the disease they might cause. In addition to causing infection, some protists are themselves vectors of infectious agents. For example, the opportunistic pathogen Acanthamoeba harbours pathogenic bacteria itself, such as Legionella . By contrast, some protists are described as key determinants in animal and plant health, due to their ability to phagocytose and therefore remove pathogenic bacteria.
Left: Antoni van Leeuwenhoek. Right: ‘Animalcules’ observed by Leeuwenhoek, ca 1795. Rijksmuseum (left); Ann Ronan Picture Library (right)/Science Photo Library
69 Microbiology Today October 2022 | microbiologysociety.org
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