Phenotypic and genetic diversity of Photobacterium damsela subsp. damsela isolated from aquatic animals in Hainan Province and Bohai Sea region

Abstract:

Photobacterium damselae subsp. damselae (PDD) is an important pathogen distributed widely in global marine environment, which could infect multiple marine organisms, and reported in various mariculture regions of China in recent years. [Objective] This study aimed to systematically compare the phenotypic and genetic diversity of PDD isolated from Hainan province and Bohai Sea region base on physiological and metabolic phenotype, virulence gene distribute and molecular genetic analysis.[Methods] The physiological and metabolic phenotypes of sucrose fermentation, moveability, hemolysis, and phospholipase activity were assayed. The profiles of pPHDD1 replication origin, dly, hlyA_pl, hlyA_ch and plpV were investigated by PCR detection. Genetic diversity of PDD was analyzed based on the toxR sequences. [Results] Four PDD strains were positive for sucrose fermentation while other twelve strains were negative. There are significant differences among the motility of PDD, in which strain Pdd1608, Pdd2009, and Pdd1704 showed strong motility. Pdd1608 isolated from Bohai Sea region exhibited strong hemolysis and phospholipase activities, whlie strain Pdd1612 and Pdd0912 isolated from Hainan Province showed weak hemolysis and none phospholipase activities, and 13 strains showed weak hemolysis and phospholipase activities. The virulence gene profile of Pdd1608 was pPHDD1 replication origin-dly-hlyA_pl-hlyA_ch-plpV, while other strains were hlyA_ch-plpV. Phylogenetic analysis suggested remarkable genetic diversity among different kinds of PDD. [Conclusion] PDD isolated from Hainan Province and Bohai Sea region were probably composed of a polyclonal bacterial population with complex phenotypic characterizations, similar virulence gene profiles, and high genetic diversity.