DNA content, kinetic complexity, and the ploidy question in Candida albicans.

Abstract

Candida albicans is a dimorphic fungus that is pathogenic for humans. No sexual cycle has been reported for this fungus, and earlier reports have differed on whether typical strains of C. albicans are haploid or diploid. Previous estimates of the DNA content of C. albicans varied by one order of magnitude. We used three independent methods to measure the kinetic complexity of the single-copy DNA from a typical strain of C. albicans (strain H317) to determine the DNA content per haploid genote; we obtained values of 15 and 20 fg per cell by using S1 nuclease and hydroxyapatite assays, respectively. Optical assays for DNA reassociation kinetics, although not definitive in themselves, yielded values in this range. Chemical measurements of the DNA content of several typical strains, including strain H317, yielded values clustered about a mean of 37 fg per cell. We concluded that these strains are diploid.Candida albicans is a dimorphic fungus, classified among the fungi imperfecti because no sexual cycle has been observed in strains of the species. Most members of the species exist in the yeast form, but the mycelial form may develop under certain conditions (23,24). Both forms of the species are pathogenic for human hosts, although the details of the pathogenicity of the two forms may be very different. Candida is the most common fungal pathogen of humans (1); clinical reports concerning the genus number in the hundreds each year (23).In contrast to the clinical reports, biochemical studies of Candida are relatively sparse. In particular, little has been established concerning the nature and organization of Candida genomes, including those of the most extensively studied species, C. albicans. Even the ploidy of C. albicans is in dispute (27,32,35,46). Several recent reports (27,28,45,46) conclude that at least some C. albicans strains are diploid, whereas results from other reports (32,35), are more simply interpreted in terms of haploidy.There have also been confficting reports of the DNA content of C. albicans strains; even values published during the last 2 years (35,39,46) disagree by nearly one order of magnitude. We present direct measurements of the total DNA content and sequence complexity of C. albicans.The determination reported here was designed specifically to include a large number of measurements to ensure a high degree of precision (2) or Stewart (41); the former procedure was modified by replacing the 0.2 M PCA wash with a 0.2 M PCA extraction (10 to 15 min on ice). We refer to these two extraction procedures as method A and method B, respectively. The supernatants of the hot PCA extractions from both methods were centrifuged at 20,000 x g for 30 min to remove substances that interfered with the diphenylamine assay. DNA was assayed colorimetrically with a diphenylamine reagent (5) and, for some experiments, also with diaminobenzoic acid reagent (37). Highly polymerized calf thymus DNA (type V, Sigma Chemical Co., St. Louis, Mo.) was used as a standard. The DNA was dried by heating at 70°C overnight...

Identification of Dermatophytes by an Oligonucleotide Array

“…The array described here was able to detect genomic DNA at levels of 1 to 10 pg per assay by testing serial 10-fold dilutions of fungal DNA (data not shown). If the DNA content of a fungal cell was equivalent to 37 fg as a yeast cell (39), then the detection limit of the array was equivalent to 27 to 270 cells per assay.…”

Genetic Analysis of Candida albicans Morphological Mutants

“…However, a deeper understanding of the biology and pathogenicity of C. albicans has been hampered by the difficulties in carrying out genetic analysis in this species. It has been suggested that most of the currently isolated C. albicans strains are diploid (Olaiya & Sogin, 1979 ;Riggsby et al, 1982) and, although contested (Sarachek, 1983), this is now widely accepted. Mitotic recombination, induced by mild UV treatment, has been used to follow the segregation of many alleles, through the formation of sectored colonies, and has provided a means for the genetic characterization of many mutants and variants (Whelan et al, 1980;Whelan & Magee, 1981 ;Whelan & Soll, 1982).…”

Quantitative differences of nuclear DNA contents and their taxonomic implications in Leucosporidium scottii, Rhodosporidium toruloides, and related basidiomycetous yeasts.

“…The average fluorescence intensity of the stationary phase cells of Saccharomyces cerevisiae haploid strain, X2180-1A, was used as a standard value and the fluorescence value was adjusted to 18, as the haploid DNA content of this organism is reported to be 18 fg (17).…”