Search

Pseudomonas plecoglossicida is an important pathogenic bacterium in aquaculture that causes visceral granulomas in large yellow croaker (Larimichthys crocea). Uridine diphosphate glucose phosphorylase encoded by galU plays a key role in biosynthesis of the bacterial envelope, particularly lipopolysaccharide and the capsule. In this study, we inactivated the galU gene in the P. plecoglossicida isolate XSDHY‐P. The galU mutant strain showed impaired growth in the early exponential stage and lacked the O polysaccharide side chain in lipopolysaccharide, but almost no defect in biofilm formation was detected. The galU mutant strain also exhibited significantly more sensitivity to the bactericidal action of normal fish serum mediated by the complement system compared to the wild‐type strain. In a cell model originating from the head kidney of large yellow croaker, the galU mutant strain showed lower capacities of adhesion, invasion, and intracellular survival compared to the wild‐type strain. In addition, the deficiency of the galU mutant drastically decreased bacterial loads in tissues and attenuated P. plecoglossicida virulence in fish. These results suggest that the galU gene of P. plecoglossicida is required for in vivo survival in large yellow croaker. [ABSTRACT FROM AUTHOR]

Pseudomonas plecoglossicida is an important pathogenic bacterial species in aquaculture, causing visceral granulomas in large yellow croaker (Larimichthys crocea) and several other economically important fish species. The GacS/GacA is a two-component regulatory system (TCS) primarily found in Pseudomonads for its role in virulence, quorum sensing, and biofilm formation. To investigate the potential role of GacS/GacA system of P. plecoglossicida , a gacS deficient mutant (Δ gacS) was generated based on a clinical isolate XSDHY-P. Compared to the wild-type (WT) strain, the Δ gacS strain showed almost no growth defect in vitro but was impaired in swimming motility and biofilm formation. Furthermore, the Δ gacS strain exhibited significantly more sensitivity to the bactericidal action of normal fish serum mediated by the complement system. In a cell model originating from the head-kidney of large yellow croaker, the Δ gacS showed lower capacities of adhesion, invasion, and intracellular survival compared to the WT strain. In addition, the virulence of the Δ gacS and WT bacterial strains were evaluated in large yellow croaker. The results showed that the deficiency of gacS drastically decreased bacterial tissue loads and substantially attenuated P. plecoglossicida virulence in fish. Furthermore, a comparative transcriptome was performed between the Δ gacS and WT strains by RNA-sequencing (RNA-seq). Transcriptomic analysis results revealed 25 upregulated and 273 downregulated genes in the Δ gacS strain compared with the WT strain, and the downregulated genes were mainly involved in flagellar assembly, metabolism, bacterial chemotaxis, and biofilm formation, which are consistent with their respective phenotypic traits. These findings will provide functional insight into the role of GacS/GacA in P. plecoglossicida. • The Δ GacS was impaired both in swimming motility and biofilm formation compared to the P. plecoglossicida WT strain. • The GacS plays a contributing role in the adhesion an invasion to LYC-hK, and in immune escaping of P. plecoglossicida. • Deletion of the GacS gene drastically attenuated the virulence of P. plecoglossicida to fish. • The results of the comparative transcriptomic analysis are consistent with their respective phenotypic traits. [ABSTRACT FROM AUTHOR]