Adaptations were carried out essentially as we have previously described [36] . Briefly, Vero-SLAM cells were infected with MeV-Alaska at an MOI of 0.1 pfu/ml and incubated in the presence of gradually increasing JMN3-003 concentrations starting at 0.5 mM. Equally infected cells treated with the virus polymerase targeted RdRp inhibitor AS-136A were examined in parallel. When cultures became over confluent, cells were reseeded for continued incubation in the presence of the same compound concentration as before. At detection of extensive cell-to-cell fusion, cellassociated viral particles were harvested, diluted 10-fold and used for parallel infections of fresh cell monolayers in the presence of compound at unchanged and doubled concentrations. Cultures treated with the highest compound concentrations in which virusinduced cytopathicity became detectable were used for further adaptation. The approach was terminated after 90 days of continued incubation or when virus-induced cytopathicity was readily detectable in the presence of 30 mM compound in accordance with previous results [36] .  Insight into the Interaction of Metal Ions with TroA from Streptococcus suis BACKGROUND: The scavenging ability of sufficient divalent metal ions is pivotal for pathogenic bacteria to survive in the host. ATP-binding cassette (ABC)-type metal transporters provide a considerable amount of different transition metals for bacterial growth. TroA is a substrate binding protein for uptake of multiple metal ions. However, the function and structure of the TroA homologue from the epidemic Streptococcus suis isolates (SsTroA) have not been characterized. METHODOLOGY/PRINCIPAL FINDINGS: Here we determined the crystal structure of SsTroA from a highly pathogenic streptococcal toxic shock syndrome (STSS)-causing Streptococcus suis in complex with zinc. Inductively coupled plasma mass spectrometry (ICP-MS) analysis revealed that apo-SsTroA binds Zn(2+) and Mn(2+). Both metals bind to SsTroA with nanomolar affinity and stabilize the protein against thermal unfolding. Zn(2+) and Mn(2+) induce distinct conformational changes in SsTroA compared with the apo form as confirmed by both circular dichroism (CD) and nuclear magnetic resonance (NMR) spectra. NMR data also revealed that Zn(2+)/Mn(2+) bind to SsTroA in either the same site or an adjacent region. Finally, we found that the folding of the metal-bound protein is more compact than the corresponding apoprotein. CONCLUSIONS/SIGNIFICANCE: Our findings reveal a mechanism for uptake of metal ions in S. suis and this mechanism provides a reasonable explanation as to how SsTroA operates in metal transport. Streptococcus suis serotype 2 (S. suis 2) is a gram-positive coccus that causes diseases in pigs and humans, and is therefore a zoonotic pathogen [1, 2] . Since the first human case of S. suis 2 infection was described in Denmark in 1968, over 400 human S. suis infection cases have been recorded thus far, covering nearly 30 countries [2, 3] . In 1998 and 2005, S. suis 2 human infections, with the new disease form of streptococcal toxic shock syndrome (STSS), had been reported in China, following the outbreaks in swine stocks initially, which caused a total of 240 human infections and claimed 52 lives [4] . Our group, in collaboration with other groups, has sequenced the entire genomes of the representatives of these two virulent S. suis 2 isolates (05ZYH33 and 98HAH12) in 2007 [5] and laid the foundation for the study of the STSS-causing S. suis 2 at the molecular level to reveal its pathogenicity [1, 6, 7] .