Predation by protozoa is one of the most important factors that control bacterial population and affect bacteria evolution in the natural environment. However, most of these studies focused on the resistance abilities of certain bacteria species. The variations at the strain level have been poorly known. The objective of this study is to investigate the bacteria strain level variations under predation stress and to correlate general predation resistance characteristics with variance survivability in microcosm experiments. Escherichia coli and Euplotes crassus were chosen as the prey and predator in this study. Predation resistance screenings were performed, followed by phenotypic tests including biofilm formation, cell aggregation, growth rate, cell size, and pathogenic gene detection....[ Read more ]

Predation by protozoa is one of the most important factors that control bacterial population and affect bacteria evolution in the natural environment. However, most of these studies focused on the resistance abilities of certain bacteria species. The variations at the strain level have been poorly known. The objective of this study is to investigate the bacteria strain level variations under predation stress and to correlate general predation resistance characteristics with variance survivability in microcosm experiments. Escherichia coli and Euplotes crassus were chosen as the prey and predator in this study. Predation resistance screenings were performed, followed by phenotypic tests including biofilm formation, cell aggregation, growth rate, cell size, and pathogenic gene detection. At last predation selection tests, which included the tests of colony persistence, and survivability tests of mixed E. coli strains under predation stress. The results showed that the E. coli strains with high survivability under ciliate predation tended to aggregate faster, forming more biofilm in the test condition, grow faster in low nutrient condition, and have smaller cell size. While the E. coli strain with low survivability share a specific pathogenic gene cdtB. The predation selection tests conducted using the mixed cultures of highest and lowest resistance E. coli strains showed that high resistance strain became the dominate of the E. coli population after 1 days’ incubation with predators. This suggests that predation could have a selection effect among different E. coli strains. In conclusion the results suggest that intraspecies diversity exists within E. coli population in terms of predation resistance, and the resistance ability may correlate with multiple phenotypic characteristics.