Polyamine-binding protein PotD2 is required for stress tolerance and virulence in Actinobacillus pleuropneumoniae

Actinobacillus pleuropneumoniae is the cause of porcine contagious pleuropneumonia, which is one of the most important respiratory diseases in swine and causes huge economic losses in the swine industry. PotD, a polyamine-binding protein, has been well characterised in many pathogens of humans and animals. In this study, a Delta potD2 mutant of A. pleuropneumoniae strain MS71 (serovar 1) was constructed successfully by homologous recombination. Growth curves of different strains showed that the growth of the Delta potD2 mutant was affected greatly in the logarithmic phase compared with that of parental strain. In vitro stress assays revealed that the viability of Delta potD2 mutant strain was significantly impaired under multiple environmental stresses, including high temperature, oxidation and hyperosmosis. Additionally, the Delta potD2 mutant caused significantly decreased mortality in a mouse model. Taken together, the findings in this study suggest an important role of PotD2 in the growth, stress tolerance and virulence of A. pleuropneumoniae.