Riemerella anatipestifer GldM is required for bacterial gliding motility, protein secretion, and virulence

Abstract

Riemerella anatipestifer is a major pathogenic agent of duck septicemic and exudative diseases. Genetic analyses suggest that this pathogen has a novel protein secretion system, known as the “type IX secretion system” (T9SS). We previously reported that deletion of the AS87_RS08465 gene significantly reduced the bacterial virulence of the R. anatipestifer strain Yb2, but the mechanism remained unclear. The AS87_RS08465 gene is predicted to encode the gliding motility protein GldM (GldM) protein, a key component of the T9SS complex. In this study, Western blotting analysis demonstrated that R. anatipestifer GldM was localized to the cytomembrane. Further study revealed that the adhesion and invasion capacities of the mutant strain RA2281 (designated Yb2Δ gldM ) in Vero cells and the bacterial loads in the blood of infected ducks were significantly reduced. RNA-Seq and PCR analyses showed that six genes were upregulated and five genes were downregulated in the mutant strain Yb2Δ gldM and that these genes were mainly involved in the secretion of proteins. Yb2Δ gldM was also found to be defective in gliding motility and protein secretion. Liquid chromatography–tandem mass spectrometry analysis revealed that nine of the proteins had a conserved T9SS C-terminal domain and were differentially secreted by Yb2Δ gldM compared to Yb2. The complementation strain cYb2Δ gldM recovered the adhesion and invasion capacities in Vero cells and the bacterial loads in the blood of infected ducks as well as the bacterial gliding motility and most protein secretion in the mutant strain Yb2Δ gldM to the levels of the wild-type strain Yb2. Taken together, these results indicate that R. anatipestifer GldM is associated with T9SS and is important in bacterial virulence. Electronic supplementary material The online version of this article (10.1186/s13567-019-0660-0) contains supplementary material, which is available to authorized users.

The Type IX Secretion System Is Required for Virulence of the Fish Pathogen Flavobacterium psychrophilum

“…Such mutants may function as attenuated vaccine strains that interact with fish and generate a protective immune response but fail to cause disease. Since T9SSs are involved in diseases caused by many related animal and human pathogens (17,21,(38)(39)(40)(41), improved understanding of F. psychrophilum virulence may have impacts beyond fish health and sustainable aquaculture.…”

“…Recent experiments demonstrate that T9SSs are required for virulence of the human pathogens Porphyromonas gingivalis and Prevotella melanogenica, the fish pathogen Flavobacterium columnare, and the bird pathogen Riemerella anatipestifer (17,21,(38)(39)(40)(41). In each case, disruption of a gene encoding a core component of the T9SS resulted in secretion defects and loss of virulence.…”

Development of a colloidal gold immunochromatographic strip for rapid detection of Riemerella anatipestifer in ducks

“…The specificity of anti-OmpA MAb was verified by Western blot ( Chen et al., 2019 ). Whole-cell bacteria of R. anatipestifer strains CH3, NJ3, and Hxb2, E. coli strains E937, DE719, and APEC01, S. enterica strains CVCC 519 and CVCC 3384, and P. multocida strain CVCC 493 were respectively mixed with loading buffer, boiled for 10 min, and loaded on the gel wells for sodium dodecyl sulfate-polyacrylamide gel electrophoresis ( SDS-PAGE ).…”

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