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Chapter 14 : Evolution of MAT in the Candida Species Complex: Sex, Ploidy, and Complete Sexual Cycles in C. lusitaniae, C. guilliermondii, and C. krusei
Category: Fungi and Fungal Pathogenesis
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Evolution of MAT in the Candida Species Complex: Sex, Ploidy, and Complete Sexual Cycles in C. lusitaniae, C. guilliermondii, and C. krusei, Page 1 of 2< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815837/9781555814212_Chap14-1.gif /docserver/preview/fulltext/10.1128/9781555815837/9781555814212_Chap14-2.gif
The best-studied species to date are the human pathogens Candida albicans and C. glabrata. However, neither of these species is as yet known to possess a complete meiotic sexual cycle. C. lusitaniae, C. guilliermondii, and C. krusei are three members of this genus that are exciting prospects for further study. Of the three species discussed in this chapter, the sexual life cycle has been the best studied for this species. Multiple types of media are capable of inducing mating including dilute potato dextrose agar, 1% malt extract media, sodium acetate, yeast carbon base, V8, and SLAD. The anamorph has been cultured from a variety of ecological niches, including human clinical specimens, insects, fruit, and decaying matter. The sexual cycle of C. guilliermondii was first identified in 1952 by Wickerham and Burton, after recognizing that some yeasts previously classified to non-ascosporeforming genera actually represented the anamorphic form of a sexual species. That sexual Candida species exist forms the basis of the argument that loss or restriction of sexual reproduction is the evolved state, possibly due to the energy expenditure required to undergo meiosis or to limit genetic exchange in a pathogen highly evolved to its host niche. Thus, continued study of the Candida species complex will provide insight on interesting evolutionary questions regarding the evolution of signal transduction pathways, sexual reproduction, commensalism, and pathogenesis.
Phylogeny of Candida anamorphic and teleomorphic species. Species are designated by the teleomorph or anamorph designation or both. An asterisk indicates the proposed point of CUG codon capture and the expansion of the MTL locus to include PAP1, OBP1, and PIK1 genes. Species with gray shading are those that encode CTG as serine rather than leucine. Black dots indicate teleomorphic species with a Candida anamorph. Node numbers are indicated above each branch. Phylogeny is adapted from Diezmann et al. (11).
Life cycle of C. lusitaniae. (A) Diagrammatic representation of the C. lusitaniae life cycle. (B) Differential interference contrast images of each stage of the C. lusitaniae life cycle. Cells of opposite mating types were incubated on dilute potato dextrose agar media, stained with DAPI (4′,6′-diamidino-2-phenylindole), and photographed at 24 to 72 h after coincubation. Scale bar is 5µm. Haploid yeast cells of opposite mating types undergo conjugation. Following conjugation one parental nuclei traverses the conjugation tube to enter the cell of the mating partner. Asci formed contain 1 to 2 clavate ascospores per ascus.
Mating-type-like loci of Candida species. (A) Depiction of the MTLα loci of C. albicans and C. lusitaniae. (B) MTLa loci of C. albicans, C. parapsilosis, and C. guilliermondii. The genes contained within the MTL loci are represented by black arrows. The genes flanking the MTL loci are depicted in white. The absence of a gene in a particular MTL locus is denoted by an X.
Candida species with known teleomorphs