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Eukaryotic Cell, June 2006, p. 916-923, Vol. 5, No. 6
1535-9778/06/$08.00+0     doi:10.1128/EC.00176-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Pneumocystis Melanins Confer Enhanced Organism Viability

Crystal R. Icenhour,1 Theodore J. Kottom,1 and Andrew H. Limper1,2*

Thoracic Diseases Research Unit, Division of Pulmonary, Critical Care and Internal Medicine,1 Department of Biochemistry and Molecular Biology, Mayo Clinic and Foundation, Rochester, Minnesota 559052

Received 24 June 2005/ Accepted 19 March 2006

Pneumocystis continues to represent an important opportunistic fungal pathogen of those with compromised immunity. Thus, it is crucial to identify factors that affect its viability and pathogenicity. We previously reported the first identification of melanins in Pneumocystis. In the present study, we sought to further characterize these components and define the function for these melanins. Melanins extracted from Pneumocystis and melanized Pneumocystis cells were analyzed by electron spin resonance spectroscopy, revealing spectra consistent with melanins from other fungi. Immunofluorescence assays using anti-melanin monoclonal antibodies showed that melanins are widely present across Pneumocystis host species, including mouse-, ferret-, and human-derived Pneumocystis organisms, as well as Pneumocystis carinii derived from rat. Using immunoelectron microscopy, melanins were found to localize to the cell wall and cytoplasm of P. carinii cysts, as well as to intracystic bodies within mature cysts. Next, the role of melanins on the maintenance of Pneumocystis viability was determined by using quantitative reverse transcription-PCR measurement of the heat shock protein mRNA under adverse environmental conditions. Using a new method to promote the melanization of Pneumocystis, we observed that strongly melanized Pneumocystis retained viability to a greater degree when exposed to UV irradiation or desiccation compared to less-pigmented organisms. These studies support our previous identification of Pneumocystis melanins across the genus, further characterize these Pneumocystis components, and demonstrate that melanins protect Pneumocystis from environmental stressors.

* Corresponding author. Mailing address: 8-24 Stabile Building, Rochester, MN 55905. Phone: (507) 284-2964. Fax: (507) 284-4521. E-mail: Limper.Andrew{at}mayo.edu.

Eukaryotic Cell, June 2006, p. 916-923, Vol. 5, No. 6
1535-9778/06/$08.00+0     doi:10.1128/EC.00176-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Sexton, A. C., Howlett, B. J. (2006). Parallels in Fungal Pathogenesis on Plant and Animal Hosts. Eukaryot Cell 5: 1941-1949 [Full Text]  
  • Nosanchuk, J. D., Casadevall, A. (2006). Impact of Melanin on Microbial Virulence and Clinical Resistance to Antimicrobial Compounds. Antimicrob. Agents Chemother. 50: 3519-3528 [Full Text]  


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