Biological Activities of Symbiotic and Parasitic Protozoa and Fungi in Low-Oxygen Environments

Recent advances in the elucidation of the metabolic capabilities of some protists living in ecosystems where oxygen concentrations are low highlight certain common features of their roles in their environments. In this review we survey the symbiotic protozoa and chytridomycete fungi of the rumen alongside parasitic protozoa infecting the human intestine and urogenital tract: many of these show striking metabolic similarities. We emphasize the putative activities of these organisms in situ as inferred by extrapolation from work with isolated organisms or axenic cultures.