Trojan horses of the microbial world: protozoa and the survival of bacterial pathogens in the environment.

Protozoa, of which there are thousands of species, are ubiquitous in diverse natural habitats such as fresh and salt water, moist soils and even dry sands. The role of freeliving protozoa in terrestrial and aquatic environments as predators of bacteria is widely acknowledged. Predation by protozoa has a significant effect in controlling bacterial populations in soil, and the degradation of bacteria undoubtedly contributes to the maintenance of soil fertility (Foster & Dormaar, 1991 ; Weekers e t al., 1993). Likewise, protozoa play an integral part in the cycling of nutrients in aquatic food chains (Porter, 1984; Wright & Coffin, 1984).

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