Characterization and functional analysis of PnuC that is involved in the oxidative stress tolerance and virulence of Streptococcus suis serotype 2

Streptococcus suis, an important swine pathogen and a major zoonotic agent, is responsible for severe financial losses in the global swine industry. Although a multitude of virulence factors have been reported, the pathogenesis of S. suis infections remains poorly understood. In our previous work, we identified a potential virulence-associated protein, named PnuC, unique to virulent strains of S. suis serotype 2 (S. suis 2). To investigate the functions of PnuC, the pnuC gene deletion mutant (ΔpnuC) was constructed in S. suis 2 strain ZY05719 to assess the phenotypic changes between ΔpnuC and the parental strain. The mutant strain ΔpnuC exhibited highly sensitive to H2O2 stress and reduced the growth ability under vigorous shaking, suggesting that PnuC contributes to the oxidative stress tolerance. Additionally, zebrafish infection model showed that the virulence of pnuC+ strains were significantly higher than pnuC- strains. Mouse infection experiments demonstrated that the abilities of ΔpnuC to colonize the tissues were significantly attenuated compared with the parental strain. Furthermore, the pnuC mutation decreased the virulence of S. suis 2 in both BALB/c mice and zebrafish infection models. Taken together, these results indicated for the first time that PnuC is involved in the oxidative stress tolerance and virulence of S. suis 2 during infection.