title: A novel non-homologous recombination-mediated mechanism for Escherichia coli unilateral flagellar phase variation.
abstract: Flagella contribute to the virulence of bacteria through chemotaxis, adhesion to and invasion of host surfaces. Flagellar phase variation is believed to facilitate bacterial evasion of the host immune response. In this study, the flnA gene that encodes Escherichia coli H17 flagellin was examined by whole genome sequencing and genetic deletion analysis. Unilateral flagellar phase variation has been reported in E. coli H3, H47 and H17 strains, although the mechanism for phase variation in the H17 strain has not been previously understood. Analysis of phase variants indicated that the flagellar phase variation in the H17 strain was caused by the deletion of an ∼35 kb DNA region containing the flnA gene from diverse excision sites. The presence of covalently closed extrachromosomal circular forms of this excised 35 kb region was confirmed by the two-step polymerase chain reaction. The deletion and complementation test revealed that the Int1157 integrase, a tyrosine recombinase, mediates the excision of this region. Unlike most tyrosine recombinases, Int1157 is suggested to recognize diverse sites and mediate recombination between non-homologous DNA sequences. This is the first report of non-homologous recombination mediating flagellar phase variation.
authors.affiliation: TEDA School of Biological Sciences and Biotechnology, Nankai University, 23 Hongda Street, TEDA, Tianjin 300457, PR China.
authors.forename: Bin
authors.initials: B
authors.lastname: Liu
authors.forename: Bo
authors.initials: B
authors.lastname: Hu
authors.forename: Zhemin
authors.initials: Z
authors.lastname: Zhou
authors.forename: Dan
authors.initials: D
authors.lastname: Guo
authors.forename: Xi
authors.initials: X
authors.lastname: Guo
authors.forename: Peng
authors.initials: P
authors.lastname: Ding
authors.forename: Lu
authors.initials: L
authors.lastname: Feng
authors.forename: Lei
authors.initials: L
authors.lastname: Wang
mesh_terms: D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000235:genetics*; D005407:Flagella / Q000502:physiology; D005408:Flagellin / Q000235:genetics*; D017353:Gene Deletion; D019426:Integrases / Q000378:metabolism; D008969:Molecular Sequence Data; D011995:Recombination, Genetic; D014158:Transcription, Genetic
chemical_list: D029968:Escherichia coli Proteins; C516095:FliC protein, E coli; D005408:Flagellin; D019426:Integrases