Evaluation of survivability of prey bacteria grazed by protozoa that are isolated and indigenous

Abstract

 Grazing experiments were conducted to evaluate survivability of prey bacteria by using three isolated bacterivorous protozoa, Spumella sp. TGKK2, Ochromonas sp. TGPH2, and Bodo sp. TGKH8. Two genetically engineered prey bacteria having marker genes were made from Cupriavidus necator KT1 and Escherichia coli K-12, respectively. Pseudomonas aeruginosa PAO1 was also used as a prey bacterium. Concentrations of these bacteria were adjusted to approximately 1~5 x 10⁸ cells/mL. Grazing rate and final concentration of prey bacterium were changed by combinations of protozoan and bacterium. In common, initial rapid decreases of prey bacteria were observed, then final bacterial concentrations became stable at a certain level ranging from 10⁴ to 10⁶ cells/mL. The genetically engineered C. necator KT1 was also used to evaluate grazing ability of indigenous protozoa in river water, and similar trend in grazing was observed.