Abstract
BackgroundAutotransporters form a large family of outer membrane proteins specifying diverse biological traits of Gram-negative bacteria. In this study, we report the identification and characterization of a novel autotransporter gene product of Burkholderia mallei (locus tag BMA1027 in strain ATCC 23344).ResultsDatabase searches identified the gene in at least seven B. mallei isolates and the encoded proteins were found to be 84% identical. Inactivation of the gene encoding the autotransporter in the genome of strain ATCC 23344 substantially reduces adherence to monolayers of HEp-2 laryngeal cells and A549 type II pneumocytes, as well as to cultures of normal human bronchial epithelium (NHBE). Consistent with these findings, expression of the autotransporter on the surface of recombinant E. coli bacteria increases adherence to these cell types by 5–7 fold. The gene specifying the autotransporter was identified in the genome of 29 B. pseudomallei isolates and disruption of the gene in strain DD503 reduced adherence to NHBE cultures by 61%. Unlike B. mallei, the mutation did not impair binding of B. pseudomallei to A549 or HEp-2 cells. Analysis of sera from mice infected via the aerosol route with B. mallei and B. pseudomallei revealed that animals inoculated with as few as 10 organisms produce antibodies against the autotransporter, therefore indicating expression in vivo.ConclusionsOur data demonstrate that we have identified an autotransporter protein common to the pathogenic species B. mallei and B. pseudomallei which mediates adherence to respiratory epithelial cells and is expressed in vivo during the course of aerosol infection.
Highlights
Autotransporters form a large family of outer membrane proteins specifying diverse biological traits of Gram-negative bacteria
Identification of a gene encoding a potential autotransporter adhesin shared by B. mallei and B. pseudomallei Comparative sequence analyses identified a gene product in the published genome of B. mallei strain ATCC 23344 that resembles the adhesins Yersinia enterocolitica YadA [2,21,52], Moraxella catarrhalis Hag [8,53,54], B. pseudomallei BoaA and BoaB [55], and B. mallei BoaA [55]
These molecules belong to the oligomeric coiled-coil adhesin (Oca) sub-family of oligomeric autotransporter proteins and have a characteristic modular organization consisting of: (i) a surfaceexposed region specifying adhesive properties termed passenger domain, (ii) a short linker region predicted to form an α helix, and (iii) a hydrophobic C-terminus composed of four β-strands anchoring the autotransporter in the outer membrane (OM) designated transporter domain [16,19,20,21]
Summary
Autotransporters form a large family of outer membrane proteins specifying diverse biological traits of Gram-negative bacteria. Autotransporter proteins are the largest known family of virulence factors expressed by Gram-negative bacteria and play prominent roles in processes such as invasion [1], serum resistance [2,3], phospholipolysis [4,5,6], cytotoxicity [7], adherence [8,9], survival within eukaryotic cells [10], intracellular motility [11], cell-to-cell aggregation [12,13], and biofilm formation [14,15] These molecules display conserved structural features including an N-terminal surface-exposed domain responsible for the biological function and a hydrophobic C-terminus that tethers the autotransporter to the outer membrane (OM). Bordetella pertussis Pertactin, an autotransporter adhesin, is a component of licensed vaccines for whooping cough (http://www. cdc.gov/vaccines/pubs/pinkbook/downloads/pert.pdf )
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