ABSTRACT
Protozoans,the natural host of the facultative intracellular pathogen Legionella species,play an important role in survival,proliferation,virulence and stress resistance of Legionella species. By repeating transformation and selection,a spontaneous mutant of plasmid over expressing green fluorescent protein was obtained. This mutant replicates and is maintained stably in Legionella cells. The colonies of L. pneumophila harbouring the mutated plasmid were intense green in colour even under the daylight. After feeding BF1 strain of Tetrahymena thermophila with transformed L. pneumophila,the intracellular dynamic of changing of bacterial shape,bacterial proliferation and lysis of the host cell due to the bacterial proliferation were observed clearly under fluorescent microscopy. Thus,the present paper provides a simple and intuitionistic strategy for investigating the ecological and cellular relationship between L. pneumophila and its host.