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Category: Clinical Microbiology; Fungi and Fungal Pathogenesis
Systematics of the Genus Cryptococcus and Its Type Species C. neoformans, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555816858/9781555815011_Chap01-1.gif /docserver/preview/fulltext/10.1128/9781555816858/9781555815011_Chap01-2.gifAbstract:
This chapter focuses on the genetic diversity of Cryptococcus species as assessed by sequence analysis of DNA. In 1935, a comprehensive study was conducted with numerous yeasts, which included 22 strains of pathogenic and nonpathogenic Cryptococci isolated from humans. Prior to the discovery of the genus Filobasidiella, the teleomorph of Cryptococcus neoformans and C. gattii, yeast taxonomists had speculated that C. neoformans belonged to the Basidiomycota for the following reasons. First, it is the only basidiomycetous genus that contains human pathogens that produce life-threatening infection of the central nervous system in immunocompromised as well as immunocompetent patients. Second, Filobasidiella is the only genus in the phylum Basidiomycota that produces long chains of basidiospores on the apex of the holobasidia by repetitive basipetal budding. Third, the genus contains two groups of species, one with and one without ontogenetic yeast stages. Due to taxonomic confusion about the status of the type species of the genus Cryptococcus, as well as the widely recognized importance of C. neoformans and C. gattii as human pathogens, the genus was neotypified by C. neoformans. This revision implies that if one uses a modern phylogenetic genus concept, only those anamorphic species that belong to the Filobasidiella clade should be classified as Cryptococcus species, e.g., C. neoformans, C. gattii, and C. amylolentus. Among the Tremellales, species classified as Cryptococcus occur intermingled with species of diverse genera such as Bullera, Tremella, Papiliotrema, Auriculibuller, Trimorphomyces, Kwoniella, Fibulobasidium, and Bulleribasidium.
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Otto Busse (1867–1922).
Francesco Sanfelice (1861–1945).
Ferdinand Curtis (1858–1937).
Basidial morphology of (A) Filobasidiella neoformans, (B) F. depauperata, and (C) F. lutea. (A and B courtesy of R. A. Samson and Antonie van Leeuwenhoek.) Bar = 5 μm.
Phylogenetic tree of representative members of the Tremellomycetes to demonstrate the diversity of the genus Cryptococcus within the four orders of the class. Neighbor joining analysis of the D1/D2 region of the LSU rDNA. Numbers at the branch nodes represent bootstrap percentages (>50%) from 1,000 full heuristic replicates (PAUP 4.0b10). Diamond symbol indicates species that have been isolated from clinical sources. The genus Filobasidiella is shaded for emphasis.
Yeast morphology of diverse non neoformans species of Cryptococcus that may occur in clinical samples. Cells were grown in yeast nitrogen base with 2% glucose for 48 h at 25°C. (A) C. laurentii CBS 139; (B) C. magnus CBS 140; (C) C. albidus CBS 142; (D) C. aerius CBS 155; (E) C. curvatus CBS 570; (F) C. humicola CBS 571; (G) C. luteolus CBS 943; (H) C. macerans CBS 2206; (I) C. gastricus CBS 2288; (J) C. gattii CBS 6955. Bar = 5 μm.