Abstract
Maintaining appropriate levels of trace elements during infection of a host is essential for microbial pathogenicity. Here we compared the uptake of 10 trace elements from 3 commonly-used laboratory media by 3 pathogens, Candida albicans, Cryptococcus neoformans and Aspergillus fumigatus, and a model yeast, Saccharomyces cerevisiae. The trace element composition of the yeasts, C. albicans, C. neoformans and S. cerevisiae, grown in rich (YPD) medium, differed primarily in P, S, Fe, Zn and Co. Speciation analysis of the intracellular fraction, which indicates the size of the organic ligands with which trace elements are complexed, showed that the ligands for S were similar in the three fungi but there were significant differences in binding partners for Fe and Zn between C. neoformans and S.cerevisiae. The profile for Cu varied across the 3 yeast species. In a comparison of C. albicans and A. fumigatus hyphae, the former showed higher Fe, Cu, Zn and Mn, while A. fumigatus contained higher P, S Ca and Mo. Washing C. albicans cells with the cell-impermeable chelator, EGTA, depleted 50–90 % of cellular Ca, suggesting that a large proportion of this cation is stored in the cell wall. Treatment with the cell wall stressor, Calcofluor White (CFW), alone had little effect on the elemental profile whilst combined Ca + CFW stress resulted in high cellular Cu and very high Ca. Together our data enhance our understanding of trace element uptake by pathogenic fungi and provide evidence for the cell wall as an important storage organelle for Ca.
Highlights
All organisms require major, minor and trace elements for growth
The background levels of trace metals in laboratory media can confound data interpretation regarding the role of micronutrient uptake systems in pathogenicity
The first aim of this study was to assess the elemental profile of commonly-used laboratory culture media and, importantly, to quantify the levels of trace elements assimilated by the human fungal pathogens C. albicans, C. neoformans and A. fumigatus
Summary
Minor and trace elements for growth. Phosphorus (P) is the most abundant as it is a key component of nucleic acids and membrane phospholipids. The metal content of cells can be accurately measured using inductively coupled plasma mass spectrometry (ICP-MS) and is enhanced by element speciation analysis, which identifies the chemical form (e.g oxidation state) of the element or size of the species (e.g. metalloprotein) to which the element is bound. This provides information about the mobility, bioavailability, impact and function of metals in biological systems (Ferrarello et al, 2002; Clemens, 2019). Element in 100 ml YPD (mg) (molarity). Element in stationary-phase % available element Element in 100 ml MSM pH Element in stationary-phase % available element yeast cell pellet from culture taken up by cells 4.5 (mg) (molarity) yeast cell pellet from culture taken up by cells in 100 ml YPD (mg) in 100 ml MSM (mg) P
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