ABC transporters and metal ions are significant for bacteria growth and virulence in Streptococcus [14] . However, only recently have insights emerged into the metal metabolism of S. suis. The adcR gene (which encodes the regulator of the Adc operon) was isolated by divalent cation deprivation [15] . Furthermore, the extracted cell surface proteins of S. suis from mutants defective in genes regulating metal ion uptake are able to confer significant protection against S. suis 2 infection in mice [16] . Previously, we identified a global zinc-response regulator of the Zur family (zinc uptake regulator) from S. suis 2 [17] , unveiling its relationship with zinc homeostasis in this organism. Whole-genome sequence analysis led to the proposition that S. suis expresses two putative transition metal transport systems, encoded by the Adc operon [15] and Tro operon (Table S1) , consistent with the situation in many other bacterial pathogens that harbor several metal transporters.