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Analysis of the Protective Capacity of Three Streptococcus suis Proteins Induced under Divalent-Cation-Limited Conditions

Department de Genètica i Microbiologia, Universitat Autònoma de Barcelona, Bellaterra, 08193 Barcelona, Spain,¹ Centre de Recerca en Sanitat Animal (CReSA), Bellaterra, 08193 Barcelona, Spain,² Servei d'Anàlisis i d'Aplicacions Microbiològiques, Universitat Autònoma de Barcelona, Bellaterra, 08193 Barcelona, Spain³

Received 19 July 2007/ Returned for modification 3 October 2007/ Accepted 2 January 2008

Streptococcus suis is a gram-positive pathogen that causes serious diseases in pigs and, in some cases, humans. Three genes of the virulent S. suis 89/1591 strain, encoding putative divalent-cation-binding lipoproteins, were isolated based on information obtained from the draft annotation files of this organism's genome. The products of these genes, which are inducible by divalent-cation deprivation, were subsequently purified, and their immunogenic and protective abilities were analyzed. All three proteins (SsuiDRAFT 0103, SsuiDRAFT 0174, and SsuiDRAFT 1237) were found to be immunogenic, but only one of them (SsuiDRAFT 0103) induced a significant protective response (87.5%, P = 0.01) against the same S. suis strain. Furthermore, the S. suis ssuiDRAFT 1240 gene (adcR), which encodes a predicted regulator of Zn²⁺ and/or Mn²⁺ uptake in streptococci, was cloned, and its protein product was purified. Electrophoretic mobility shift assays with purified S. suis AdcR protein showed experimentally, for the first time, that the AdcR DNA-binding sequence corresponds to the TTAACNRGTTAA motif. In addition, a requirement for either Zn²⁺ or Mn²⁺, but not Fe²⁺, to establish in vitro binding of AdcR to its target sequence and the ability of AdcR to bind the ssuiDRAFT 0103 and ssuiDRAFT 1237 gene promoters but not the promoter of the ssuiDRAFT 0174 gene were demonstrated. Taken together, these data suggest that SsuiDRAFT 0103 is a good candidate for vaccines against S. suis and support preliminary results indicating that bacterial envelope proteins involved in the uptake of divalent cations other than iron may be useful for protective purposes.

Published ahead of print on 22 January 2008.

Editor: V. J. DiRita