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Infection and Immunity, September 2002, p. 5225-5235, Vol. 70, No. 9
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.9.5225-5235.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Molecular Genetic Analyses of Mating Pheromones Reveal Intervariety Mating or Hybridization in Cryptococcus neoformans

Vishnu Chaturvedi,^1,2* Jinjiang Fan,^1, Birgit Stein,¹ Melissa J. Behr,³ William A. Samsonoff,⁴ Brian L. Wickes,⁵ and Sudha Chaturvedi¹

Mycology,¹ Anatomic Pathology Laboratories,³ Electron Microscopy Core, Wadsworth Center, New York State Department of Health,⁴ Department of Biomedical Sciences, School of Public Health, State University of New York, Albany, New York,² Department of Microbiology, University of Texas Health Sciences Center at San Antonio, San Antonio, Texas⁵

Received 15 March 2002/ Returned for modification 15 May 2002/ Accepted 12 June 2002

The sexual mating of the pathogenic yeast Cryptococcus neoformans is important for pathogenesis studies because the fungal virulence is linked to the mating type (MAT). We characterized C. neoformans mating pheromones (MF 1 and MFa1) from 122 strains to understand intervariety hybridization or mating and intervariety virulence. MF 1 in three C. neoformans varieties showed (a) specific nucleotide polymorphisms, (b) different copy numbers and chromosomal localizations, and (c) unique deduced amino acids in two geographic populations of C. neoformans var. gattii. MF 1 of different varieties cross-hybridized in Southern hybridizations. Their phylogenetic analyses showed purifying selection (neutral evolution). These observations suggested that MAT strains from any of the three C. neoformans varieties could mate or hybridize in nature with MATa strains of C. neoformans var. neoformans. A few serotype A/D diploid strains provided evidence for mating or hybridization, while a majority of A/D strains tested positive for haploid MF 1 identical to that of C. neoformans var. grubii. MF 1 sequence and copy numbers in diploids were identical to those of C. neoformans var. grubii, while their MFa1 sequences were identical to those of C. neoformans var. neoformans; thus, these strains were hybrids. The mice survival curves and histological lesions revealed A/D diploids to be highly pathogenic, with pathogenicity levels similar to that of the C. neoformans var. grubii type strain and unlike the low pathogenicity levels of C. neoformans var. neoformans strains. In contrast to MF 1 in three varieties, MFa1 amplicons and hybridization signals could be obtained only from two C. neoformans var. neoformans reference strains and eight A/D diploids. This suggested that a yet undiscovered MFa pheromone(s) in C. neoformans var. gattii and C. neoformans var. grubii is unrelated to, highly divergent from, or rarer than that in C. neoformans var. neoformans. These observations could form the basis for future studies on the role of intervariety mating in C. neoformans biology and virulence.

Editor: R. N. Moore

Present address: Mammalian Cell Genetics Group, Health Sector, N.R.C. Biotechnology Research Institute, Montreal, Quebec, Canada H4P 2R2.

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