Distribution and characterization of N-acylhomoserine lactone (AHL)-degrading activity and AHL lactonase gene (qsdS) in Sphingopyxis

N -Acylhomoserine lactone (AHL)-degrading enzyme is identified from the various environments and applied for quorum-sensing inhibition. In this study, we isolated two AHL-degrading strains, Sphingopyxis sp. EG6 and FD7, from the industrial cooling water samples. When the eight Sphingopyxis type strains were checked for the AHL-degrading activity, two strains, Sphingopyxis alaskensis DSM 13593 and Sphingopyxis bauzanensis DSM 22271, showed high AHL-degrading activity. The complete genome sequences of EG6 and FD7 revealed the presence of gene homolog of qsdS , which encodes AHL-lactonase in Sphingomonas ursincola . The qsdS gene is seated between putative gene homologs involved in 3-isopropylmalate dehydratase large ( leuC2 ) and small ( leuD ) subunits in the genome of EG6, FD7, DSM 13593, and DSM 22271, but completely disappeared between leuC2 and leuD in the genome sequences of Sphingopyxis type strains without AHL-degrading activity. Purified His-tagged QsdS showed high AHL-degrading activity and catalyzed AHL ring opening by hydrolyzing lactones. In addition, heterologous expression of qsdS in Pseudomonas aeruginosa resulted in reduction of biofilm formation. These results suggested that the AHL-degrading activity in Sphingopyxis is useful as an effective agent for biofilm inhibition.