Riemerella anatipestifer GldG is necessary for secretion of effectors by type IX secretion system

Riemerella anatipestifer secretes proteins through the type IX secretion system (T9SS). Recent studies have shown that the R. anatipestifer T9SS component proteins GldM and GldK also act as crucial virulence factors. In our previous study, the disruption of AS87_RS00460 gene, which encodes the predicted protein GldG, significantly reduced the bacterial virulence of R. anatipestifer wild-type strain Yb2, but the mechanism was unclear. In this study, we investigated the function of the GldG in bacterial virulence and protein secretion using the mutant strain Yb2 Delta gldG and complementation strain cYb2 Delta gldG. Our results demonstrate that the gldG gene encodes a gliding-motility-associated ABC transporter substrate-binding protein GldG, which was localized to the bacterial membrane in an immunoblotting analysis, and functions in the bacterium's adherence to and invasion of host cells and its survival in host blood. The resistance of mutant strain Yb2 Delta gldG to complement-dependent killing was significantly reduced. Yb2 Delta gldG displayed reduced gliding motility and deficient protein secretion. Labelfree quantification (LFQ) with liquid chromatography-mass spectrometry (LC-MS) showed that 10 proteins with a conserved T9SS C-terminal domain were differentially secreted by Yb2 Delta gldG and Yb2. The secretion levels of those 10 proteins were determined with immunoblotting, and the results were consistent with the LFQ LC-MS data. All of these effects were rescued by complementation with a plasmid encoding Yb2 gldG. Our results demonstrate that the R. anatipestifer gldG gene encodes the protein GldG, which is involved in bacterial virulence and protein secretion.

Automated summary

Riemerella anatipestifer secretes proteins through the type IX secretion system (T9SS), and GldM and GldK are found to be crucial virulence factors. This study reveals that the gldG gene encodes the GldG protein, which plays a key role in bacterial virulence and protein secretion. The mutant strain Yb2 Delta gldG shows reduced gliding motility and deficient protein secretion.