The Metallophore Staphylopine Enables Staphylococcus aureus To Compete with the Host for Zinc and Overcome Nutritional Immunity

Abstract

During infection, the host sequesters essential nutrients, such as zinc, to combat invading microbes. Despite the ability of the immune effector protein calprotectin to bind zinc with subpicomolar affinity, Staphylococcus aureus is able to successfully compete with the host for zinc. However, the zinc importers expressed by S. aureus remain unknown. Our investigations have revealed that S. aureus possesses two importers, AdcABC and CntABCDF, which are induced in response to zinc limitation. While AdcABC is similar to known zinc importers in other bacteria, CntABCDF has not previously been associated with zinc acquisition. Concurrent loss of the two systems severely impairs the ability of S. aureus to obtain zinc and grow in zinc-limited environments. Further investigations revealed that the Cnt system is responsible for the ability of S. aureus to compete with calprotectin for zinc in culture and contributes to acquisition of zinc during infection. The cnt locus also enables S. aureus to produce the broad-spectrum metallophore staphylopine. Similarly to the Cnt transporter, loss of staphylopine severely impairs the ability of S. aureus to resist host-imposed zinc starvation, both in culture and during infection. Further investigations revealed that together staphylopine and the Cnt importer function analogously to siderophore-based iron acquisition systems in order to facilitate zinc acquisition by S. aureus. Analogous systems are found in a broad range of Gram-positive and Gram-negative bacterial pathogens, suggesting that this new type of zinc importer broadly contributes to the ability of bacteria to cause infection.

Intracellular accumulation of staphylopine impairs the fitness of Staphylococcus aureus cntE mutant

“…The fitness defect of DcntE mutant associated with intracellular StP accumulation occurred in both metal-depleted laboratory media as well as in sites of infection. Our work and that of others showed that Fe or Zn availability repressed the expression of cntKLM [17][18][19]. Besides StP, S. aureus produces other siderophores including SA and SB [11].…”

“…The fitness defect in abscesses caused by absence of CntE in S. aureus is largely due to staphylopine accumulation Cnt-StP-mediated iron and zinc uptake contributes to the virulence of S. aureus during infection [17,18]. We previously found that the DcntE mutant in S. aureus MW2 background exhibits a growth defect in murine subcutaneous abscesses, which was not observed in the DcntABCDF mutant [20].…”

“…The expression of the cnt operon in S. aureus is upregulated under metal starvation conditions and in infection sites that have low levels of available free iron, zinc, and manganese [16][17][18][19][20]. Thus, it was interesting to evaluate if the expression of StP synthesis genes in the DcntE mutant was altered under metaldepleted conditions compared with the WT.…”

“…The ninegene cntKLMABCDFE operon is required for StP synthesis and trafficking. The cnt operon expression is upregulated in metal-depleted conditions [17][18][19][20] and repressed by Fur and Zur in the presence of iron and zinc, respectively [19]. The cnt operon expression is upregulated in metal-depleted conditions [17][18][19][20] and repressed by Fur and Zur in the presence of iron and zinc, respectively [19].…”

Independent and cooperative regulation of staphylopine biosynthesis and trafficking by Fur and Zur

“…We further demonstrated that it could also import copper, zinc and iron in vitro , functioning with the metallophore Sp synthetized by three genes belonging to the same locus as cntABCDF (Ghssein et al ., ). During the review process of this study, a work focused on the zinc transporters of S. aureus has been published, confirming that CntABCDF was implicated in zinc acquisition and identifying AdcA as a zinc‐binding protein of a zinc transporter (Grim et al ., ). In the present study, we reveal that CntABCDF transporter is necessary for optimal growth in zinc‐deprived medium (Fig.…”