Wor1‐regulated ferroxidases contribute to pigment formation in opaque cells of Candida albicans

Abstract

Candida albicans is a harmless commensal resident in the human gut and a prevalent opportunistic pathogen. A key part of its commensalism and pathogenesis is its ability to switch between different morphological forms, including white‐to‐opaque switching. The Wor1 protein was previously identified as a master regulator of white‐to‐opaque switching in mating type locus (MTL) homozygous cells. The mechanisms by which the dark color of the opaque colonies is controlled and the pimpled surface of opaque cells is formed remain unknown. Candida albicans produces melanin pigment in vitro and during infection. However, the molecular mechanism underlying the regulation of melanin production is unclear. In this study, we demonstrated that ferroxidases (Fets) function as pigment multicopper oxidases and regulate the production of dark‐pigmented melanin in opaque cells. The FET genes presented distinct regulation patterns in response to different extracellular stimuli. In YPD (1% yeast extract, 2% peptone and 2% dextrose)‐rich medium, four of the five FET genes were up‐regulated by Wor1, especially at the human body temperature of 37 °C. In minimal medium with low ammonium concentrations, all five FET genes were up‐regulated by Wor1. However, at high ammonium concentrations, some FET genes were down‐regulated by Wor1. Wor1‐up‐regulated Fets contributed to dark pigment formation in opaque colonies, but not to the elongated shape of these opaque cells. Increased melanin externalization was associated with the pimpled surface of the opaque cells. Melanized C. albicans cells were more resistant to fungal clearance. Deletion of the five FET genes completely blocked melanin production in opaque cells and resulted in the generation of white elongated ‘opaque’ cells. In addition, the up‐regulated Fets are important for defense against oxidant attacks. The functional diversity of Fets may reflect the multiple strategies of C. albicans to rapidly adapt to diverse host niches.

Melanization of Candida auris Is Associated with Alteration of Extracellular pH

“…One unexplored aspect of C. auris physiology is whether it can produce the virulence factor melanin. Other Candida species, such as C. albicans and C. glabrata, produce this virulence factor [ 8 , 9 , 10 , 11 ]. Melanin is a black-brown, insoluble, acid-resistant pigment found throughout a plethora of life forms, and it has particular importance in the context of fungal virulence in mammals [ 12 , 13 ].…”

Melanization ofCandida aurisis Associated with Alteration of Extracellular pH

“…Interestingly, the supernatant of the non-melanized CDC 387 strain has a yellow tint to it, which indicates that some molecules are being released in higher amounts compared with the CDC 381 and CDC 388 strains. This pH-based mechanism of fungal melanization differs greatly from other ways in which fungi produce melanin, including C. albicans (9)(10)(11). In C. albicans, melanization is mediated by ferroxidases, a class of enzymes that are genetically similar to the melanin-producing enzyme laccase in C. neoformans.…”

“…These results in C. auris would suggest that a laccase does not exist as it does in C. neoformans , or at least not one with as much of a wide-ranging substrate range. Melanization in other DOPA-melanin producing fungi is often catalyzed by laccases (50) or multicopper ferroxidases (11). Current annotation of the C. auris genome indicate there are hypothetical laccases, oxidoreductase, and ferroxidases (Ontology Groups OG6_100257 and OG6_100380), however these appear to be related to metal ion homeostasis and part of the peroxisomal membrane.…”

“…One unexplored aspect of C. auris physiology is whether it can produce the virulence factor melanin. Other Candida species, such as C. albicans and C. glabrata, produce this virulence factor (8)(9)(10)(11). Melanin is a black-brown, insoluble, acid resistant pigment found throughout a plethora of life forms, and it has particular importance in the context of fungal virulence in mammals (12,13).…”

“…This pH-based mechanism of fungal melanization differs greatly from other ways in which fungi produce melanin, including C. albicans (9)(10)(11). In C. albicans, melanization is mediated by ferroxidases, a class of enzymes that are genetically similar to the melanin-producing enzyme laccase in C. neoformans.…”