Acquisition of Mn(II) in Addition to Fe(II) Is Required for Full Virulence of Salmonella enterica Serovar Typhimurium

Abstract

The roles of the genes feoB (ABC ferrous iron transporter), mntH (proton-dependent manganese transporter), and sitABCD (putative ABC iron and/or manganese transporter) in Salmonella pathogenicity were investigated by using mutant strains deficient in one, two, or three transporters. Our results indicated that sitABCD encodes an important transporter of Mn(II) and Fe(II) which is required for full virulence in susceptible animals (Nramp1 ؊/؊ ) and for replication inside Nramp1 ؊/؊ macrophages in vitro. The mntH sitABCD double mutant (mutant MS) showed minimal Mn(II) uptake and increased sensitivity to H 2 O 2 and to the divalent metal chelator 2,2-dipyridyl (DP) and was defective for replication in macrophages. In vivo MS appeared to be as virulent as the sitABCD mutant in Nramp1 ؊/؊ animals. The ferrous iron transporter Feo was required for full virulence in 129/Sv Nramp1 ؊/؊ mice, and infection with multiple mutants lacking FeoB was not fatal. The sitABCD feoB mutant (mutant SF) and the mntH sitABCD feoB mutant (mutant MSF) showed minimal Fe(II) uptake and were slightly impaired for replication in susceptible macrophages. MSF showed reduced growth in minimal medium deficient in divalent cations. The role of the mntH gene, which is homologous to mammalian Nramp genes, was also investigated after overexpression in the double mutant MS. MntH preferred Mn(II) over Fe(II) and could suppress MS sensitivity to H 2 O 2 and to DP, and it also improved the intracellular survival in Nramp1 ؊/؊ macrophages. This study indicates that acquisition of Mn(II), in addition to Fe(II), is required for intracellular survival and replication of Salmonella enterica serovar Typhimurium in macrophages in vitro and for virulence in vivo.

Interferon‐γ limits the availability of iron for intramacrophage Salmonella typhimurium

“…This idea is consistent with the finding that Lcn2 is able to export iron through the cell surface membrane via LcnR [24]. However, even in the presence of Lcn2, iron entering Salmonella-containing phagolysosomes may still be available for these microbes by siderophore-independent strategies such as feo-mediated ferrous iron import [11]. This assumption is supported by our data on the preserved capacity to acquire approximately half-maximal amounts of iron by the siderophore-deficient Salmonella strain Figure 5.…”

“…38: 1923-1936 Immunity to infection In humans, the central importance of IFN-c for immune response against salmonellae is highlighted by the fact that patients with genetic defects in the IL-12-induced production of IFN-c or in the IFN-c receptor 1 selectively suffer from infections with salmonellae and otherwise weakly pathogenic mycobacteria since their phagocytes fail to eliminate these microbes [8,9]. Iron serves as an essential nutrient for nearly all pathogenic microorganisms, and the expression of iron acquisition systems by infectious agents is associated with their virulence as this trace element is essential for microbial growth and proliferation [10,11]. In infections with intracellular parasites, including Salmonella serovars, the interplay between the activity of IFN-c and iron homeostasis within macrophages is a central battlefield deciding about the course of the disease [12,13].…”

“…On the other hand, non-siderophorebound ferrous iron is taken up by Feo, a pathway that may be most relevant in microenvironments with low oxygen tension [18]. Of note, both siderophore-dependent and -independent mechanisms of iron uptake are linked to bacterial virulence [11,19,20]. Remarkably, mammals have evolved an innate defense mechanism which specifically interferes with siderophore-mediated iron uptake by microbes; lipocalin 2 (Lcn2) is secreted by neutrophils and macrophages in response to bacterial infections and captures iron-laden microbial siderophores [21,22].…”

“…Iron serves as an essential nutrient for nearly all pathogenic microorganisms, and the expression of iron acquisition systems by infectious agents is associated with their virulence as this trace element is essential for microbial growth and proliferation [10,11]. In infections with intracellular parasites, including Salmonella serovars, the interplay between the activity of IFN-c and iron homeostasis within macrophages is a central battlefield deciding about the course of the disease [12,13].…”

Impact of Usp18 and IFN signaling in Salmonella-induced typhlitis

“…The strain was rendered resistant to streptomycin by transformation with the pHP45omega vector using standard electroporation technique as previously described. 39 The Salmonella Typhimurium SL1344 (NCTC 13347) strain naturally resistant to streptomycin was obtained from the National Collection of Type Cultures.…”