Dimorphism and haploid fruiting in Cryptococcus neoformans: association with the alpha-mating type.

Abstract

Cryptococcus neoformans is a major opportunistic fungal pathogen in AIDS and other immunosuppressed patients. We have shown that wild-type haploid C. neoformans can develop an extensive hyphal phase under appropriate conditions. Hyphae produced under these conditions are monokaryotic, possess unfused clamp connections, and develop basidia with viable basidiospores. The ability to undergo this transition is determined by the presence of the a-mating type locus and is independent of serotype. The association of the hyphal phase with the a-mating type may explain the preponderance of this mating type in the environment and the nature of the infectious propagule of C. neoformans.Since the discovery of the sexual or perfect state of the human fungal pathogen Cryptococcus neoformans by Kwon-Chung (1, 2), it has been considered a bipolar heterothallic basidiomycete with two mating types, a and a (MA Ta and MA Ta The ability of hyphae to form fruiting body-like structures in the vegetative phase is called monokaryotic, homokaryotic, or haploid fruiting (13). Although haploid fruiting is common in the higher basidiomycetes (13-15), it has not been characterized in C. neoformans, and association with mating type has never been described. Recent observations made in this laboratory and a reassessment of past studies (5, 10, 16) allow us to propose a new hypothesis for the biased mating type ratios and the nature of the infectious propagule of C. neoformans. We show here that a strains of C. neoformans can undergo a true dimorphic transition from a haploid yeast phase to a hyphal phase from which vegetative growth can continue indefinitely. The hyphal phase is induced by nitrogen starvation on a solid surface. Basidia bearing viable basidiospores are also produced, all of which are a in mating type. The ability of a but not a cells to form basidiospores under these conditions provides an attractive explanation for both the mating type bias and the nature of the infectious propagule of C. neoformans. MATERIALS AND METHODSStrains. The strains used in this study are listed in Table 1. Auxotrophic strains were derived from JEC20 (MA Ta) and JEC21 (MA Ta). JEC20 and JEC21 are a well-characterized, haploid, congenic pair of prototrophic laboratory strains that presumably differ only at the mating type locus (17).Media 7327The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Aislamiento de Cryptococcus gattii serotipo B a partir de detritos de Eucalyptus spp. en Colombia.

“…La amplificación del gen de la pareja sexual a en todos los aislamientos pudiera indicar la presencia de una población clonal, sugiriendo que esta clonalidad puede influenciar, o ser influenciada, por la ausencia de la pareja sexual opuesta en la naturaleza y limitar así su recombinación (36,37). Se ha encontrado que la prevalencia de la pareja sexual α sobre la pareja sexual a se debe a la gran capacidad de la primera de llevar a cabo el proceso de fructificación haploide en ausencia de la pareja sexual opuesta (1,38,39). Sin embargo, esta prevalencia de la pareja sexual α sobre la a varía según lo han reportado diversos autores en varias regiones australianas; en Adelaida, al sur de Australia, se ha encontrado una proporción α:a de 26:0; en Queensland (sureste de Australia), 15:0; en New South Wales 2:27, lo cual sugiere en todos ellos que se está llevando a cabo una reproducción clonal; mientras que en Renmark (noroeste de Australia), la proporción fue 10:6, lo que indica la posibilidad de que se esté presentando recombinación sexual entre los aislamientos (37).…”

Phenotypic Switching of Cryptococcus neoformans and Cryptococcus gattii

“…Clinical C. gattii strains were found to be less diverse in different studies [25,32] and often are typed as serotype B, MATalpha strains with a typical VGI molecular type [14]. C. gattii is predominantly clonal, and except for the newly emerged RG strain in Canada, the majority to C. gattii strains are not fertile and cannot generate haploid spores by monokaryotic fruiting [33]. Recently investigations from our laboratory have demonstrated that a clinical C. gattii strain can also undergo phenotypic switching [34].…”

Cativeiro de aves como fonte de Cryptococcus neoformans na cidade de Campo Grande, Mato Grosso do Sul, Brasil

“…neoformans é adquirida através da inalação de propágulos de origem ambiental 15 , representados por leveduras desidratadas, menores que 2mm de diâmetro, facilmente aerossolizadas. Sugeriu-se que basidiósporos da forma sexuada do fungo, medindo 1,8 x 2,5mm, mais resistentes à dessecação, mais facilmente aerossolizados e comprovadamente patogênicos para animais de laboratório, também possam ser inalados 31 .…”