Effects of Disrupting the Polyketide Synthase Gene WdPKS1 in Wangiella [Exophiala] Dermatitidis on Melanin Production and Resistance to Killing by Antifungal Compounds, Enzymatic Degradation, and Extremes in Temperature

BMC Microbiol. 2006 Jun 19;6:55. doi: 10.1186/1471-2180-6-55.

Abstract

Background: Wangiella dermatitidis is a human pathogenic fungus that is an etiologic agent of phaeohyphomycosis. W. dermatitidis produces a black pigment that has been identified as a dihydroxynaphthalene melanin and the production of this pigment is associated with its virulence. Cell wall pigmentation in W. dermatitidis depends on the WdPKS1 gene, which encodes a polyketide synthase required for generating the key precursor for dihydroxynaphthalene melanin biosynthesis.

Results: We analyzed the effects of disrupting WdPKS1 on dihydroxynaphthalene melanin production and resistance to antifungal compounds. Transmission electron microscopy revealed that wdpks1Delta-1 yeast had thinner cell walls that lacked an electron-opaque layer compared to wild-type cells. However, digestion of the wdpks1Delta-1 yeast revealed small black particles that were consistent with a melanin-like compound, because they were acid-resistant, reacted with melanin-binding antibody, and demonstrated a free radical signature by electron spin resonance analysis. Despite lacking the WdPKS1 gene, the mutant yeast were capable of catalyzing the formation of melanin from L-3,4-dihyroxyphenylalanine. The wdpks1Delta-1 cells were significantly more susceptible to killing by voriconazole, amphotericin B, NP-1 [a microbicidal peptide], heat and cold, and lysing enzymes than the heavily melanized parental or complemented strains.

Conclusion: In summary, W. dermatitidis makes WdPKS-dependent and -independent melanins, and the WdPKS1-dependent deposition of melanin in the cell wall confers protection against antifungal agents and environmental stresses. The biological role of the WdPKS-independent melanin remains unclear.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antifungal Agents / pharmacology*
  • Cold Temperature
  • Dose-Response Relationship, Drug
  • Drug Resistance, Fungal / genetics
  • Electron Spin Resonance Spectroscopy / methods
  • Enzyme Stability / genetics
  • Exophiala / drug effects
  • Exophiala / enzymology*
  • Exophiala / ultrastructure
  • Hot Temperature
  • Melanins / biosynthesis*
  • Miconazole / pharmacology
  • Microscopy, Electron, Scanning / methods
  • Microscopy, Electron, Transmission / methods
  • Microscopy, Fluorescence / methods
  • Mutation / genetics
  • Naphthols
  • Polyketide Synthases / chemistry
  • Polyketide Synthases / genetics
  • Polyketide Synthases / metabolism*

Substances

  • 1,8-dihydroxynaphthalene melanin
  • Antifungal Agents
  • Melanins
  • Naphthols
  • Polyketide Synthases
  • Miconazole