Preliminary studies on the different roles of T6SSs in pathogenicity of Pseudomonas plecoglossicida NB2011

Abstract

Pseudomonas plecoglossicida, the causative agent of visceral granulomas in the large yellow croaker (Larimichthys crocea) in China, encodes three sets of type Ⅵ secretion systems (T6SS1‐3). The purpose of this study was to characterize the different roles of T6SSs involved in infection. In‐frame deletion of T6SSs was constructed, which resulted in 8 mutants. Competition against E. coli DH5α, virulence against the croaker and in vivo survival ability of the mutants were tested. The expression and secretion of Hcp by P. plecoglossicida NB2011 were investigated. The results showed T6SS2 mutant failed to inhibit the growth of E. coli, which is an indication of T6SS2 acting against environmental bacteria. The LD50 value of T6SS1 mutant strongly increased; T6SS2 and T6SS3 mutants were similar to that of the wild type; and the virulence of double deletion or triple deletion mutant was drastically alleviated, indicating that T6SS1 being one of the major virulence factors, and T6SS2 and T6SS3 directly or indirectly being involved in the pathogenicity. T6SS1 mutant disappeared in the fish spleen in 3 days, while other strains kept increasing, indicating the T6SS1 stimulation bacteria replication in vivo. Hcp1 secreted at 12–28°C and Hcp2 secreted at 12–35°C, while Hcp3 secretion not detected in vitro. This study has thrown some insights on the understanding of pathogenicity mechanisms of this pathogen.

The bacterial pathogen Pseudomonas plecoglossicida, its epidemiology, virulence factors, vaccine development, and host–pathogen interactions

“…Similar results were revealed by Jin et al. (2021), and further work demonstrated that T6SS2 and T6SS3 are involved in host infection, as combined deletion of both T6SS2 and T6SS3 or all three systems almost abolished the bacterial virulence (Jin et al. 2021).…”

“…The T6SSs were demonstrated to play important roles during infection: T6SS1 mutation was found to abrogate most of the virulence against croakers, with no visceral granulomas developing in the infected fish (Tao et al 2020); and T6SS2 majorly contributed to bacterial competition (Li et al 2022a). Similar results were revealed by Jin et al (2021), and further work demonstrated that T6SS2 and T6SS3 are involved in host infection, as combined deletion of both T6SS2 and T6SS3 or all three systems almost abolished the bacterial virulence (Jin et al 2021). Knockdown of clpV or impB, which are T6SS ATPase-encoding genes, also resulted in strongly attenuated pathogen virulence (Luo et al 2019a;Liu et al 2020), verifying the essential roles of T6SSs during infection.…”

“…(2021), and further work demonstrated that T6SS2 and T6SS3 are involved in host infection, as combined deletion of both T6SS2 and T6SS3 or all three systems almost abolished the bacterial virulence (Jin et al. 2021). Knockdown of clpV or impB , which are T6SS ATPase‐encoding genes, also resulted in strongly attenuated pathogen virulence (Luo et al.…”

Effect of Ferredoxin Receptor FusA on the Virulence Mechanism of Pseudomonas plecoglossicida

“…Bacterial virulence is usually affected by environmental factors. For example, the pathogenic temperature of “visceral white spot disease” caused by P. plecoglossicida in large yellow croaker and other commercial fish is 15°C–20°C ( Zhang et al., 2018a ; Kaur et al., 2019 ; Lv et al., 2019 ; Huang et al., 2020a ; Hu et al., 2021 ; Jin et al., 2021 ). The results of various stress experiments showed that compared with 18°C, the expression level of fusA was significantly downregulated at 4°C, 12°C, and 37°C.…”