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Related Experiment Videos

Redox buffering by melanin and Fe(II) in Cryptococcus neoformans

E S Jacobson1, J D Hong

  • 1Hunter Holmes McGuire Veterans Affairs Medical Center, Richmond, Virginia 23249, USA. jacobson.eric_s@richmond.va.gov

Journal of Bacteriology
|September 1, 1997
PubMed
Summary

Fungal melanin acts as a redox buffer, but its electron source was unknown. Researchers found that iron(II) reduces fungal melanin, enhancing its buffering capacity and supporting a model of fungal redox cycling for pathogenesis.

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Area of Science:

  • Mycology
  • Biochemistry
  • Electrochemistry

Background:

  • Fungal melanin serves as an extracellular redox buffer, potentially neutralizing antimicrobial oxidants.
  • The source of reducing equivalents for fungal melanin has remained unidentified.
  • The role of externally generated iron(II) in reducing fungal melanin and promoting pathogenesis was investigated.

Purpose of the Study:

  • To determine if iron(II) generated by fungal ferric reductase can reduce fungal melanin.
  • To investigate the effect of iron(II) on the redox properties and buffering capacity of melanin.
  • To establish a model for the physiological redox cycling of fungal melanin.

Main Methods:

  • Electrochemical analysis of melanin film electrodes exposed to varying concentrations of iron(II) and oxidants/reductants.

Related Experiment Videos

  • Measurement of melanin's open-circuit potential (OCP) and cyclic voltammetric reduction wave.
  • Spectrophotometric analysis of melanin and melanized Cryptococcus neoformans suspensions treated with iron(II).
  • Quantification of iron(II) generated by Cryptococcus neoformans cultures.

    • Main Results:

    • Iron(II) exposure decreased melanin's OCP and the area of its reduction wave, indicating reduction.
    • Iron(II) increased melanin's buffering capacity by 44%, a significant increase not observed with dithionite.
    • Iron(II) treatment reduced light absorption by melanin and melanized C. neoformans, confirming melanin reduction.
    • Cryptococcus neoformans cultures produced measurable levels of extracellular iron(II).

    Conclusions:

    • Iron(II) can reduce fungal melanin under physiological conditions and binds to it.
    • Iron(II) cooperatively enhances the redox buffering capacity of melanin.
    • The findings support a model where fungal extracellular iron(II) maintains the reducing capacity of melanin for redox cycling and pathogenesis.