Riemerella anatipestifer Endonuclease I displays enzymatic activity and is associated with bacterial virulence.

Riemerella anatipestifer is an important pathogen of waterfowl, causing septicemic and exudative diseases. We previously reported that the R. anatipestifer AS87_RS02625 is a secretory protein of the type IX secretion system (T9SS). In this study, R. anatipestifer T9SS protein AS87_RS02625 was determined to be a functional Endonuclease I (EndoI), which has DNase and RNase activities. Optimal temperature and pH of the recombinant R. anatipestifer EndoI (rEndoI) to cleave λDNA were determined as 55-60 °C and 7.5 respectively. The DNase activity of the rEndoI was dependent on the presence of divalent metal ions. Presence of Mg ²⁺ at a concentration range of 7.5-15 mM in the rEndoI reaction buffer displayed the highest DNase activity. In addition, the rEndoI displayed RNase activity to cleave MS2-RNA (ssRNA), either in the absence or presence of divalent cations Mg ²⁺ , Mn ²⁺ , Ca ²⁺ , Zn ²⁺ and Cu ²⁺ . The DNase activity of the rEndoI was significantly enhanced by Mg ²⁺ , Mn ²⁺ and Ca ²⁺ but not Zn ²⁺ and Cu ²⁺ . Moreover, we indicated that R. anatipestifer EndoI functioned on the bacterial adherence, invasion, in vivo survival and inducing inflammatory cytokines. These results indicate that the R. anatipestifer T9SS protein AS87_RS02625 is a novel EndoI, displays endonuclease activity and plays an important role in bacterial virulence.
Competing Interests: Conflict of Interest The authors declare no conflict of interest.
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