Acquisition of transition row metal ions from the environment is critical for the virulence of the pneumococcus. It has previously been reported that the import of zinc relies upon the ABC transporter substrate-binding proteins (SBPs) AdcA and AdcAII, and that these proteins act in a redundant fashion¹. Here we present sequence and structural analyses indicating that there are two major differences between the SBPs. We hypothesized that these features could give rise to differences in zinc-binding properties and mechanisms of zinc acquisition of the two proteins. We demonstrate that the polyhistidine triad (Pht) proteins, which are another family of molecules found at the cell surface², are vital for the acquisition of zinc by AdcAII, but are less important for that of AdcA. This was supported by in vitro analyses of the metal binding properties of AdcA and Pht proteins, growth curve measurements, and the use of animal models of disease comparing the virulence of mutant strains lacking adcA, adcAII, phtABDE and combinations thereof. This work therefore increases our understanding of the molecular mechanisms by which the pneumococcus obtains zinc, and also provides the first clear evidence that the Pht proteins are involved in metal ion homeostasis in vivo.