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Processes in Microbial Ecology$
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David L. Kirchman

Print publication date: 2011

Print ISBN-13: 9780199586936

Published to Oxford Scholarship Online: December 2013

DOI: 10.1093/acprof:oso/9780199586936.001.0001

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Predation and protists

Predation and protists

(p.117) Chapter 7 Predation and protists
Processes in Microbial Ecology

David L. Kirchman

Oxford University Press

This chapter focuses on the role of protozoa (purely heterotrophic protists) and other protists in grazing on other microbes. Heterotrophic nanoflagellates, 3–5 microns long, are the most important grazers of bacteria and small phytoplankton in aquatic environments. In soils, flagellates are also important, followed by naked amoebae, testate amoebae, and ciliates. Many of these protists feed on their prey by phagocytosis, in which the prey particle is engulfed into a food vacuole into which digestive enzymes are released. This mechanism of grazing explains many factors affecting grazing rates, such as prey numbers, size, and composition. Ingestion rates increase with prey numbers before reaching a maximum, similar to the Michaelis-Menten equation describing uptake as a function of substrate concentration. Protists generally eat prey that are about 10-fold smaller than the equivalent spherical diameter of the protistan predator. In addition to flagellates, ciliates and dinoflagellates are often important predators in the microbial world, and are critical links between microbial food chains and larger organisms. Many protists, especially in aquatic habitats, are capable of photosynthesis. In some cases, the predator benefits from photosynthesis carried out by engulfed, but undigested, photosynthetic prey or its chloroplasts.

Keywords:   top-down control, phagocytosis, Lotka-Volterra model, trophic transfer efficiency, mixotrophy, endosymbiotic theory

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