Recent lateral gene transfer from Pasteurella multocida into Haemophilus influenzae
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Haemophilus influenzae is a gram-negative bacterium that exclusively colonizes humans. Nonencapsulated strains of the bacterium are found in the upper respiratory tract of healthy humans, but can also cause the respiratory diseases otitis media, bronchitis, and pneumonia. Many of the chromosomal genes of H. influenzae were acquired by lateral transfer from other bacterial genera. Recently, we investigated a cluster of unusually virulent nonencapsulated H. influenzae implicated in human invasive disease. An island between aspA and groES in which a urease gene cluster present in H. influenzae had been replaced by a homolog of Neisseria meningitides mtrF was discovered (Erwin et al., 2005). We compared the aspA-groES region with that of Pasteurella multocida, a member of the same family of bacteria. The two genomes have scattered synteny and share about 83% of their DNA. Both species have natural genetic transformation and use the same recognition site for DNA uptake. The mtrF gene is found between aspA and groES in P. multocida, within a somewhat larger island that includes a homolog of fsxA. The H. influenzae mtrF island is 95-100% identical to the region in P. multocida, as compared to 80% similarity in flanking genes. The direction of transfer is indicated by the presence of pseudogene fragments of fsxA persisting in H. influenzae. Because MtrF contributes to erythromycin resistance in Neisseria, we hypothesized that the gene transfer event occurred during the antibiotic era. To test this hypotheisis, we collaborated with Dr. Vivek Kapur (University of Minnesota) to test isolates of P. multocida from domestic poultry and wild fowl for the presence of mtrF. Long and inverse PCR was used to identify genes between aspA and groES in six wild-type Pasteurella genomes. This is the first report of gene exchange between H. influenzae and a pathogen of our domestic species.