The role of manganese in morphogenesis and pathogenesis of the opportunistic fungal pathogen Candida albicans

Metals such as Fe, Cu, Zn, and Mn are essential trace nutrients for all kingdoms of life, including microbial pathogens and their hosts. During infection, the mammalian host attempts to starve invading microbes of these micronutrients through responses collectively known as nutritional immunity. Nutritional immunity for Zn, Fe and Cu has been well documented for fungal infections; however Mn handling at the host-fungal pathogen interface remains largely unexplored. This work establishes the foundation of fungal resistance against Mn associated nutritional immunity through the characterization of NRAMP divalent metal transporters in the opportunistic fungal pathogen, Candida albicans. Here, we identify C. albicans Smf12 and Smf13 as two NRAMP transporters required for cellular Mn accumulation. Single or combined smf12 & UDelta;/& UDelta; and smf13 & UDelta;/& UDelta; mutations result in a 10-80 fold reduction in cellular Mn with an additive effect of double mutations and no losses in cellular Cu, Fe or Zn. As a result of low cellular Mn, the mutants exhibit impaired activity of mitochondrial Mn-superoxide dismutase 2 (Sod2) and cytosolic Mn-Sod3 but no defects in cytosolic Cu/Zn-Sod1 activity. Mn is also required for activity of Golgi mannosyltransferases, and smf12 & UDelta;/& UDelta; and smf13 & UDelta;/& UDelta; mutants show a dramatic loss in cell surface phosphomannan and in glycosylation of proteins, including an intracellular acid phosphatase and a cell wall Cu-only Sod5 that is key for oxidative stress resistance. Importantly, smf12 & UDelta;/& UDelta; and smf13 & UDelta;/& UDelta; mutants are defective in formation of hyphal filaments, a deficiency rescuable by supplemental Mn. In a disseminated mouse model for candidiasis where kidney is the primary target tissue, we find a marked loss in total kidney Mn during fungal invasion, implying host restriction of Mn. In this model, smf12 & UDelta;/& UDelta; and smf13 & UDelta;/& UDelta; C. albicans mutants displayed a significant loss in virulence. These studies establish a role for Mn in Candida pathogenesis. Author summaryNutritional immunity is the host withholding of nutrients including metals from microbial pathogens during infection. A great deal is understood regarding nutritional immunity for Zn, Cu and Fe during fungal infections, but very little is known about Mn and fungal pathogenesis. Using the opportunistic and polymorphic fungal pathogen Candida albicans as a model, we describe a host immune response involving Mn during Candida infection and demonstrate the importance of Mn for fungal virulence. Our studies reveal two divalent metal transporters in C. albicans, namely Smf12 and Smf13, that are needed for Mn accumulation, for Mn dependent enzymes involved in oxidative stress resistance and protein glycosylation, for proper formation of the mannose layer of the cell wall and for hyphal morphogenesis. Using a mouse model of systemic candidiasis, we document a restriction in host Mn that occurs through decreased Mn levels upon Candida invasion of the kidney. C. albicans survives this host restriction of Mn and both Smf12 and Smf13 contribute to virulence. These findings on Mn at the host-fungal pathogen interface are likely to be extrapolated to other fungal pathogens of public health importance.