Coming of Age—Sexual Reproduction in Candida Species

Historically, Candida species represented a catch-all taxonomic grouping for yeasts that exhibited hyphal or pseudohyphal branching and did not form sexual spores. However, with the advent of molecular typing of DNA sequences, it is now apparent that Candida represent a diverse range of species within the Hemiascomycetes, which also includes the model yeast Saccharomyces cerevisiae. Several Candida species are prominent human pathogens, including Candida glabrata, Candida parapsilosis, and Candida albicans, the latter being the most common human pathogenic fungus. While C. albicans is a natural commensal, typically found amongst the microbiota inhabiting the gastrointestinal tract, it is also the cause of debilitating mucosal infections as well as life-threatening systemic infections. Taken together, Candida species are the fourth most common cause of nosocomial bloodstream infections, where they account for 8%–10% of such infections [1]. The most clinically important Candida species, with the exception of C. glabrata and Candida krusei, cluster together in a single clade [2]. The species within this clade share an altered genetic code in which CUG codons encode serine rather than the universal leucine [3]. The Candida clade species can be further subdivided into two separate sub-clades; one contains haploid species that are relatively rare pathogens (e.g., Candida lusitaniae), while the other contains diploid species such as C. albicans and C. parapsilosis that are frequent pathogens (Figure 1A).