摘要Objective CRISPR-Cas protects bacteria from exogenous DNA invasion and is associated with bacterial biofilm formation and pathogenicity.Methods We analyzed the type I-F CRISPR-Cas system of Legionella pneumophila WX48,including Cas1,Cas2-Cas3,Csy1,Csy2,Csy3,and Cas6f,along with downstream CRISPR arrays.We explored the effects of the CRISPR-Cas system on the in vitro growth,biofilm-forming ability,and pathogenicity of L.pneumophila through constructing gene deletion mutants.Results The type I-F CRISPR-Cas system did not affect the in vitro growth of wild-type or mutant strains.The biofilm formation and intracellular proliferation of the mutant strains were weaker than those of the wild type owing to the regulation of type IV pili and Dot/Icm type IV secretion systems.In particular,Cas6f deletion strongly inhibited these processes.Conclusion The type I-F CRISPR-Cas system may reduce biofilm formation and intracellular proliferation in L.pneumophila.