Flagellar gene fliP contributes to the virulence of Pseudomonas plecoglossicida by regulating its motility.

As an opportunistic causative pathogen of "Visceral White Spot Disease" in several kinds of teleost, Pseudomonas plecoglossicida has caused huge economic losses to aquaculture. Flagella is the motility organ of bacteria as well as a vital virulence factor. The protein encoded by the fliP gene is involved in the formation of the flagellar type III secretion export apparatus, which plays a crucial role in flagellar assembly. In this study, the Δ fliP and C-Δ fliP strains of P. plecoglossicida were constructed to explore the biological profiles mediated by the fliP gene and its effects on the virulence of this organism. Compared to the wild type strain (NZBD9) of P. plecoglossicida , the deletion strain Δ fliP exhibited a significant impairment in swimming motility, chemotaxis, adhesion, and biofilm formation abilities. The transcriptomic analysis of the NZBD9, Δ fliP and C-Δ fliP strains revealed that the fliP gene may affect the biological profiles of P. plecoglossicida by down-regulating the expression of flagellar assembly, type 6 secretion system and bacterial chemotaxis related genes. Furthermore, the results of artificial infection showed that the virulence of Δ fliP strain to hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) was attenuated, with a LD 50 value of 2.5 × 104 CFU/fish. These findings demonstrate that the fliP gene contributes to the virulence of P. plecoglossicida by regulating its motility. • Δ fliP strain was constructed by a two-step allelic exchange from P. plecogerossicida NZBD9 strain. • Deletion of fliP significantly reduced pathogenicity of P. plecoglossicida to hybrid grouper. • Δ fliP exhibited a significant impairment in swimming motility, chemotaxis, adhesion, and biofilm formation abilities. • Δ fliP down-regulated the expression of flagellar assembly, type 6 secretion system and bacterial chemotaxis related genes. [ABSTRACT FROM AUTHOR]