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Infection and Immunity, February 2004, p. 774-781, Vol. 72, No. 2
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.2.774-781.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Investigation of a Novel DNase of Streptococcus suis Serotype 2{dagger}

Michael C. Fontaine,{ddagger} Jose Perez-Casal, and Philip J. Willson*

Vaccine & Infectious Disease Organization, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5E3, Canada

Received 1 May 2003/ Returned for modification 28 July 2003/ Accepted 23 October 2003

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 (rSsnA{Delta}) confirmed that SsnA is expressed in vivo. Furthermore, anti-rSsnA{Delta} 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.

* Corresponding author. Mailing address: Vaccine & Infectious Disease Organization, 120 Veterinary Rd., Saskatoon, Saskatchewan, S7N 5E3, Canada. Phone: (306) 966-7480. Fax: (306) 966-7478. E-mail: Willson{at}sask.usask.ca.

{dagger} Published as number 328 in the Vaccine & Infectious Disease Organization journal series.

Editor: V. J. DiRita

{ddagger} Present address: Moredun Research Institute, Penicuik EH26 0PZ, Scotland, United Kingdom.

Infection and Immunity, February 2004, p. 774-781, Vol. 72, No. 2
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.2.774-781.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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