Natural heterozygosity in Candida albicans

Abstract

The authors subjected 16 C. albicans clinical isolates to ultraviolet radiation and tested the survivors for auxotrophy. Six isolates displayed strongly biased auxotroph spectra: three yielded methionine auxotrophs, two yielded both isoleucinevaline and adenine auxotrophs, and one yielded lysine auxotrophs. We present evidence that auxotrophs arise by segregation from naturally occurring heterozygous states. The remaining isolates yielded few or no auxotrophs in an arbitrary sample (>2,500) of survivors of irradiation. The experiments indicate that C. albicans is diploid, although aneuploidy (2n + i) cannot be rigorously excluded. The possible utility of heterozygosity as a marker in epidemiological studies, and a rationale for the frequent occurrence of heterozygosity is discussed.