title: An RTX operon in hemolytic Moraxella bovis is absent from nonhemolytic strains.
abstract: Pathogenic isolates of Moraxella bovis express a calcium-dependent transmembrane pore forming cytotoxin that is an RTX toxin encoded by mbxA. The DNA flanking mbxA was cloned and sequenced to determine if M. bovis contained a classical RTX operon. Open reading frames (ORFs) with deduced amino acid sequence homology to putative activation (RTX C) and transport (RTX B and D) proteins were identified and have been designated MbxC, MbxB, and MbxD, respectively. Thus, hemolytic M. bovis contains a typical RTX operon comprised of four genes arranged (5'-3') mbxCABD. In addition, the deduced amino acid sequences of DNA flanking mbxCABD revealed ORFs with amino acid sequence similarity to transposases (5'). At the 3' end of the mbx gene cluster, an ORF with homology to bacterial tolC genes was identified. Thus, as with the cya RTX operon of Bordetella pertussis, M. bovis appears to have a secretion accessory protein linked to RTX genes. Analysis of genomic DNA isolated from 5 nonhemolytic M. bovis strains by PCR and Southern blotting revealed the absence of mbxCABD. These strains did, however, amplify with primers specific for the 5' region flanking mbxC. M. bovis harbors a classical RTX operon that is absent in nonhemolytic strains.
authors.affiliation: Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, 2108 Tupper Hall, Davis 95616, USA. jaangelos@ucdavis.edu
authors.forename: John A
authors.initials: JA
authors.lastname: Angelos
authors.forename: John F
authors.initials: JF
authors.lastname: Hess
authors.forename: Lisle W
authors.initials: LW
authors.lastname: George
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics*; D001427:Bacterial Toxins / Q000737:chemistry / Q000235:genetics*; D001483:Base Sequence; D015139:Blotting, Southern / Q000662:veterinary; D015153:Blotting, Western / Q000662:veterinary; D002417:Cattle; D002418:Cattle Diseases / Q000382:microbiology; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology / Q000662:veterinary; D007639:Keratoconjunctivitis, Infectious / Q000382:microbiology; D008969:Molecular Sequence Data; D016955:Moraxella bovis / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification; D009876:Operon / Q000235:genetics*; D016133:Polymerase Chain Reaction / Q000662:veterinary; D011994:Recombinant Proteins / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004269:DNA, Bacterial; D011994:Recombinant Proteins