ABC transport systems that contain an A-1 family SBP have emerged as key transporters that are required for virulence in several bacterial pathogens [33] . To better understand the significant role of the Tro operon for metal transition in S. suis, we screened the S. suis 2 genome [5] for orthologs of known metaldependent enzymes and metal transporters as described previously [30] (Table S1 ). We identified 23 Zn-dependent proteins and three Mn-dependent proteins. Mn plays a key role in the growth of S. suis [47, 48] , whereas S. suis does not encode orthologs of either Mn 2+ -specific MntH transporter or the P-type ATPase, MntA. Moreover, another putative transition metal system in S. suis, the Adc operon was found to exhibit homology to the S. pneumonia Adc operon, the latter is an ABC-type Zn permease [49] . These data imply that SsTroA maybe plays an adaptive role in vivo, likely modulated by SsTroR expression in response to specific environmental conditions.