Protozoan Density and the Coexistence of Protozoan Predators and Bacterial Prey
1978
Habte, M. | Alexander, M.
Low numbers of Tetrahymena pyriformis provided with °2 x 10⁹ Klebsiella pneumoniae or Rhizobium sp. cells/ml reduced the bacterial population only to 10⁷/ml in solution. When 5—7 x 10⁸ K. pneumoniae or 1 x 10⁸ Rhizobium sp. were preyed upon, 10⁶ bacteria/ml survived and coexisted with the ciliate. Low initial densities of the protozoan provided with 3 x 10⁶ or 5 x 10⁷ K. pneumoniae or 3—4 x 10⁷ Rhizobium sp./ml reduced the prey population t 2—3 x 10⁵/ml. However, when the initial number of T. pyriformis was high (2—34 x 10⁴/ml) and the K. pneumonia or Rhizobium sp. density was °10⁷/ml, the animal did not reduce the bacterial population size. The data suggest that the number of K. pneumoniae or Rhizobium sp. cells able to coexist in solution with T. pyriformis was governed by the number of protozoa initially present or developing as a result of predation. By contrast, 10⁵ Xanthomonas citri cells/ml coexisted with the ciliate whether this bacterium was provided at 7 x 10⁶ or 8 x 10⁸ cells/ml. In soil treated with 3.5 x 10⁸ and 3.1 x 10⁹ Rhizobium sp./g, the density of indigenous protozoa rose to 1—2 x 10⁴ and 4—5 x 10⁵/g, respectively, yet the density of rhizobial survivors stabilized at 3—7 x 10⁷/g, a range higher than that observed in solution.
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