title: Diversity of secretion systems associated with virulence characteristics of the classical bordetellae.
abstract: Secretion systems are key virulence factors, modulating interactions between pathogens and the host's immune response. Six potential secretion systems (types 1-6; T1SS-T6SS) have been discussed in classical bordetellae, respiratory commensals/pathogens of mammals. The prototypical Bordetella bronchiseptica strain RB50 genome seems to contain all six systems, whilst two human-restricted subspecies, Bordetella parapertussis and Bordetella pertussis, have lost different subsets of these. This implicates secretion systems in the divergent evolutionary histories that have led to their success in different niches. Based on our previous work demonstrating that changes in secretion systems are associated with virulence characteristics, we hypothesized there would be substantial divergence of the loci encoding each amongst sequenced strains. Here, we describe extensive differences in secretion system loci; 10 of the 11 sequenced strains had lost subsets of genes or one entire secretion system locus. These loci contained genes homologous to those present in the respective loci in distantly related organisms, as well as genes unique to bordetellae, suggesting novel and/or auxiliary functions. The high degree of conservation of the T3SS locus, a complex machine with interdependent parts that must be conserved, stands in dramatic contrast to repeated loss of T5aSS 'autotransporters', which function as an autonomous unit. This comparative analysis provided insights into critical aspects of each pathogen's adaptation to its different niche, and the relative contributions of recombination, mutation and horizontal gene transfer. In addition, the relative conservation of various secretion systems is an important consideration in the ongoing search for more highly conserved protective antigens for the next generation of pertussis vaccines.
authors.affiliation: 1​ Department of Veterinary and Biomedical Sciences, Pennsylvania State University, University Park, PA, USA 2​ Graduate Program in Bioinformatics and Genomics, Pennsylvania State University, University Park, PA, USA.
authors.forename: Jihye
authors.initials: J
authors.lastname: Park
authors.affiliation: 1​ Department of Veterinary and Biomedical Sciences, Pennsylvania State University, University Park, PA, USA.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: 3​ Department of Food Science, Pennsylvania State University, University Park, PA, USA.
authors.forename: Chun
authors.initials: C
authors.lastname: Chen
authors.affiliation: 3​ Department of Food Science, Pennsylvania State University, University Park, PA, USA.
authors.forename: Edward G
authors.initials: EG
authors.lastname: Dudley
authors.affiliation: 1​ Department of Veterinary and Biomedical Sciences, Pennsylvania State University, University Park, PA, USA 4​ Singapore Centre on Environmental Life Sciences Engineering, Lee Kong Chian School of Medicine, Nanyang Technological University, Singapore.
authors.forename: Eric T
authors.initials: ET
authors.lastname: Harvill
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D058947:Bacterial Secretion Systems / Q000235:genetics / Q000378:metabolism*; D001885:Bordetella Infections / Q000382:microbiology*; D016950:Bordetella bronchiseptica / Q000145:classification / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D001886:Bordetella pertussis / Q000145:classification / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity*; D006801:Humans; D010802:Phylogeny; D014774:Virulence
chemical_list: D001426:Bacterial Proteins; D058947:Bacterial Secretion Systems