HYS // Gene Cluster Contributes to Its Pathogenicity toward .

HYS is more virulent than toward but the mechanism underlying virulence is unclear. This study is the first to report that the specific gene cluster / in HYS is involved in the virulence of this strain toward , and there are no reports of GtrA, GtrB and GtrII in any species. The pathogenicity of HYS was evaluated using as a host. Based on the prediction of virulence factors and comparative genomic analysis of HYS, we identified 42 specific virulence genes in HYS. Slow-killing assays of these genes showed that the mutation had the greatest effect on the virulence of HYS, and GtrA, GtrB and GtrII all positively affected HYS virulence. Two critical GtrII residues (Glu and Lys) were identified in HYS. Transmission electron microscopy (TEM) showed that GtrA, GtrB and GtrII were involved in the glucosylation of lipopolysaccharide (LPS) O-antigen in HYS. Furthermore, colony-forming unit (CFU) assays showed that GtrA, GtrB and GtrII significantly enhanced HYS colonization in the gut of , and glucosylation of LPS O-antigen and colonization in the host intestine contributed to the pathogenicity of HYS. In addition, experiments using the worm mutants ZD101, KU4 and KU25 revealed a correlation between HYS virulence and the TIR-1/SEK-1/PMK-1 pathways of the innate immune p38 MAPK pathway in . In conclusion, these results reveal that the specific virulence gene cluster // contributes to the unique pathogenicity of HYS compared with other pathogenic , and that this process also involves innate immunity. These findings significantly increase the available information about GtrA/GtrB/GtrII-based virulence mechanisms in the genus .