Intracellular growth of L. pneumophila Lp ΔclpP mutant in A. castellanii was abolished. A. castellanii cells were seeded onto 24-well plates and infected with L.pneumophila at an MOI of 10. At each time point indicated, amoebae cells were lysed and the CFU was determined by plating dilutions onto BCYE plates. The intracellular growth kinetics of JR32, LpΔclpP mutant, clpP complemented strain, and dotA mutant are shown. The infection assay was carried out in triplicate.