Abstract: OBJECTIVE To construct small RNA phrs gene deletion and complementation strains from Pseudomonas aeruginosa and observe the effect of the phrs on the bacterial growth, and biofilm formation.METHODS The λ-Red recombination system was used to generate the phrs deletion strain (PA27853Δphrs), complementary strain (PA27853Δphrs-comp), and control strain (PA27853Δphrs-control) of P.aeruginosa.The growth curves were drawn to assess the effect of phrs on the bacterial growth.Fluorescent staining assay was carried out for quantitative analysis of the change of ability of biofilm formation.RESULTS The phrs deletion and complementation strains were constructed successfully.The RT-PCR showed that the phrs gene was re-expressed in complementary strain but was not expressed in deletion strain.The phrs gene did not have effect on the speed of bacterial growth, the ability of biofilm formation was remarkably reduced after the gene deletion,however, the biofilms were remarkably formed in the complementation strains.CONCLUSION PA27853Δphrs strain is successfully constructed by λ-Red recombination technology.The phrs gene plays an important role in regulating the biofilm formation of P.aeruginosa.