title: Horizontal gene transfer and assortative recombination within the Acinetobacter baumannii clinical population provide genetic diversity at the single carO gene, encoding a major outer membrane protein channel.
abstract: We described previously the presence in Acinetobacter baumannii of a novel outer membrane (OM) protein, CarO, which functions as an L-ornithine OM channel and whose loss was concomitant with increased carbapenem resistance among clonally related nosocomial isolates of this opportunistic pathogen. Here, we describe the existence of extensive genetic diversity at the carO gene within the A. baumannii clinical population. The systematic analysis of carO sequences from A. baumannii isolates obtained from public hospitals in Argentina revealed the existence of four highly polymorphic carO variants among them. Sequence polymorphism between the different A. baumannii CarO variants was concentrated in three well-defined protein regions that superimposed mostly to predicted surface-exposed loops. Polymorphism among A. baumannii CarO variants was manifested in differential electrophoretic mobilities, antigenic properties, abilities to form stable oligomeric structures, and l-ornithine influx abilities through the A. baumannii OM under in vivo conditions. Incongruence between the phylogenies of the clinical A. baumannii isolates analyzed and those of the carO variants they harbor suggests the existence of assortative (entire-gene) carO recombinational exchange within the A. baumannii population. Exchange of carO variants possessing differential characteristics mediated by horizontal gene transfer may constitute an A. baumannii population strategy to survive radically changing environmental conditions, such as the leap from inanimate sources to human hosts and vice versa, persistence in a compromised host, and/or survival in health care facilities.
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR-CONICET), Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas, Universidad Nacional de Rosario, Suipacha 531, 2000 Rosario, Argentina.
authors.forename: María Alejandra
authors.initials: MA
authors.lastname: Mussi
authors.forename: Adriana S
authors.initials: AS
authors.lastname: Limansky
authors.forename: Verónica
authors.initials: V
authors.lastname: Relling
authors.forename: Pablo
authors.initials: P
authors.lastname: Ravasi
authors.forename: Adrián
authors.initials: A
authors.lastname: Arakaki
authors.forename: Luis A
authors.initials: LA
authors.lastname: Actis
authors.forename: Alejandro M
authors.initials: AM
authors.lastname: Viale
mesh_terms: D000151:Acinetobacter Infections / Q000382:microbiology; D040981:Acinetobacter baumannii / Q000235:genetics* / Q000302:isolation & purification; D000595:Amino Acid Sequence; D000942:Antigens, Bacterial / Q000737:chemistry / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D001118:Argentina; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D022761:Gene Transfer, Horizontal; D014644:Genetic Variation; D006761:Hospitals; D006801:Humans; D008969:Molecular Sequence Data; D009952:Ornithine / Q000378:metabolism; D010802:Phylogeny; D055503:Protein Multimerization; D011995:Recombination, Genetic; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid
chemical_list: D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D004269:DNA, Bacterial; D009952:Ornithine