Investigation of a novel DNase of Streptococcus suis serotype 2.
A secreted nuclease, SsnA, was identified in the virulent Streptococcus suis isolate SX332 and subsequently in each of the type strains of capsular serotypes 1 through 9. Screening of 258 porcine clinical isolates from surface (nasal mucosa or palatine tonsil) or internal (joint, brain or other internal organ) locations revealed a significant relationship (P < 0.001) between expression of nuclease and isolation from an internal site. A 3,126-bp gene, ssnA, was identified from a phenotypically nuclease-negative pGh9:ISS1 insertion mutant, and analysis of the predicted SsnA sequence revealed a 35-amino-acid (aa) secretion signal sequence, a 22-aa DNA-binding domain, and a typical gram-positive cell wall sorting motif. A requirement of Ca2+ and Mg2+ for SsnA activity was determined, and the substrate specificity was found to be for single- and double-stranded linear DNA. Reverse transcription-PCR experiments revealed that ssnA is expressed throughout all stages of S. suis growth, and Western blots with porcine anti-S. suis immune sera against a recombinant, truncated SsnA derivative (rSsnADelta) confirmed that SsnA is expressed in vivo. Furthermore, anti-rSsnADelta antibodies were sufficient to neutralize SsnA activity. Analyses of subcellular fractions of SX332 and derived mutants, on DNA-containing polyacrylamide gels and by Western blotting, suggest that SsnA is cell wall located.
Fontaine
Michael C
MC
Vaccine & Infectious Disease Organization, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E3, Canada.
Perez-Casal
Jose
J
Willson
Philip J
PJ
D000595:Amino Acid Sequence; D000818:Animals; D002473:Cell Wall / Q000201:enzymology; D003851:Deoxyribonucleases / Q000235:genetics / Q000302:isolation & purification* / Q000502:physiology; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016366:Open Reading Frames; D011817:Rabbits; D017011:Streptococcus suis / Q000201:enzymology* / Q000472:pathogenicity; D013552:Swine; D014774:Virulence
D003851:Deoxyribonucleases