Abstract
Pasteurella multocida, a Gram-negative opportunistic pathogen, has led to a broad range of diseases in mammals and birds, including fowl cholera in poultry, pneumonia and atrophic rhinitis in swine and rabbit, hemorrhagic septicemia in cattle, and bite infections in humans. In order to better interpret the genetic diversity and adaptation evolution of this pathogen, seven genomes of P. multocida strains isolated from fowls, rabbit and pigs were determined by using high-throughput sequencing approach. Together with publicly available P. multocida genomes, evolutionary features were systematically analyzed in this study. Clustering of 70,565 protein-coding genes showed that the pangenome of 33 P. multocida strains was composed of 1,602 core genes, 1,364 dispensable genes, and 1,070 strain-specific genes. Of these, we identified a full spectrum of genes related to virulence factors and revealed genetic diversity of these potential virulence markers across P. multocida strains, e.g., bcbAB, fcbC, lipA, bexDCA, ctrCD, lgtA, lgtC, lic2A involved in biogenesis of surface polysaccharides, hsf encoding autotransporter adhesin, and fhaB encoding filamentous haemagglutinin. Furthermore, based on genome-wide positive selection scanning, a total of 35 genes were subject to strong selection pressure. Extensive analyses of protein subcellular location indicated that membrane-associated genes were highly abundant among all positively selected genes. The detected amino acid sites undergoing adaptive selection were preferably located in extracellular space, perhaps associated with bacterial evasion of host immune responses. Our findings shed more light on conservation and distribution of virulence-associated genes across P. multocida strains. Meanwhile, this study provides a genetic context for future researches on the mechanism of adaptive evolution in P. multocida.
Highlights
Pasteurella multocida, a Gram-negative rod-shaped bacterium, is the type species of the genus Pasteurella (Christensen and Bisgaard, 2006)
Seven P. multocida strains were chosen for whole genome shotgun sequencing, including three strains C51-2, C51-3, C51-17 isolated from rabbit, two strains Pm724 and Pm731 isolated from goose, strain C48-1 isolated from chicken, and strain C44-1 isolated from pig (Table 1)
Together with 26 publicly available and high quality genome sequences of P. multocida, a comprehensive investigation was carried out to study pangenome characterization, genetic diversity of virulence genes, and evolutionary selection forces operating on the protein-coding genome of this zoonotic pathogen
Summary
Pasteurella multocida, a Gram-negative rod-shaped bacterium, is the type species of the genus Pasteurella (Christensen and Bisgaard, 2006). Pasteurella multocida is an opportunistic pathogen that can cause multihost diseases, characterized by fowl cholera in poultry, pneumonia and atrophic rhinitis in swine, hemorrhagic septicemia in cattle and rabbit, and bite infections in humans (Boyce et al, 2010). These diseases have led to huge economic losses to the livestock and poultry industry worldwide (Ghaffar and Tariq, 2016). To explore genetic content of virulence genes in P. multocida, the first complete genome sequence of the avian strain Pm70 has been reported in 2001 (May et al, 2001). Using genome sequences of 11 haemorrhagic septicaemia (HS) strains and four other P. multocida strains, a recent study by Moustafa et al (2015) has revealed 96 HS-specific genes which could promote the development of disease-specific diagnostic tests
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