Genomic variation in C. albicans.

Candida albicans displays many types of variation which affect a broad spectrum of phenotypes. Among them are antigenic, chromosomal, morphologic, and biochemical variation. The ability to modulate many phenotypes is clearly an important factor in the success of this fungus as a pathogen and variation at the genomic level may be the common denominator among the different systems. Genomic variation in C. albicans has been studied by many researchers and a number of different mechanisms have been identified. Among them are ploidy fluctuations, which allow the organism to cycle from 2n chromosome number to 4n or higher; translocation, which has been demonstrated to involve many different chromosomes and affects many phenotypes including virulence; mitotic recombination, which has been demonstrated to increase resistance to certain drugs; and nondisjunction, which has been shown to have morphological consequences. The number and diversity of these mechanisms combine to make C. albicans a highly successful organism. Although normally a commensal of humans, when invasive, C. albicans can inhabit almost any site in the body. It is not known what governs the transition of C. albicans from a commensal to pathogenic invader, however, variation at the genomic level likely plays a role. One possible consequence of variation is the generation of atypical strains, further expanding the documented phenotypic plasticity of this organism. The exposure of patients to cytotoxic drugs during treatment of such diseases as AIDS or cancer increases the selective pressure and has exacerbated both the frequency and degree of variability observed in C. albicans. The molecular analysis of genomic variation in C. albicans is proving to be a fertile area of research and future investigations can only be expected to add to the mechanisms documented in this review.