RESUMO
Previous studies have revealed the occurrence of multiple chromosomal alterations among spontaneous colony form mutants and clinical isolates of Candida albicans. In this report we show that such karyotype alterations are also seen in spontaneous and induced non-germinative mutants of the fungus. To determine if phenotypic changes other than colony form and microscopic morphology accompanied the rearrangements of the electrophoretic karyotype, we studied the following characteristics of the non-germinative and some of the colony form mutants: formation of pseudohyphae, chlamydospore production, germ tube formation, colony morphology, auxotrophy, growth at various temperatures, and colony morphology and pigment formation on selected media (bismuth sulphite and Phloxine B). We established that phenotypic and karyotypic variability among spontaneous, non-germinative mutants was no different than such variability among spontaneous colony form mutants. Thus, non-germination may represent another phenotypic consequence of genomic instability in C. albicans. The variability in different phenotypic attributes that occurred amongst the mutants was not associated with any given karyotype. Moreover, neither the low nor the high phenotypic variabilities observed were explained by the relatively high number of alterations in a limited number of chromosomes.
Assuntos
Candida albicans/genética , Candida albicans/crescimento & desenvolvimento , Candida albicans/isolamento & purificação , Cromossomos Fúngicos , DNA Fúngico/genética , DNA Fúngico/isolamento & purificação , Eletroforese em Gel de Campo Pulsado , Variação Genética , Humanos , Cariotipagem , Mutação , Fenótipo , Sondas RNARESUMO
We previously described 14 rare spontaneous morphological mutants of Candida albicans that were associated with chromosomal aberrations (E. P. Rustchenko-Bulgac, F. Sherman, and J. B. Hicks, J. Bacteriol. 172:1276-1283, 1990). Improved conditions for separation of chromosomes, as well as hybridization probes, were used to investigate the variation of karyotypes of clinical isolates and additional morphological mutants. All 23 newly analyzed morphological mutants, representing frequently occurring and highly unstable colonial forms, had a variety of altered karyotypes. All chromosomal changes were similar to those previously observed in mutants m1 to m14. In this study, I particularly noted that the most frequent changes involved the long chromosome VIII, which carries ribosomal DNA cistrons. Two rates of instability were uncovered by analyzing the progenies from two highly unstable mutants. An unstable mutant proved to be able to continuously produce a large number of altered karyotypes that could result in a wide variety of different phenotypes. Furthermore, all four independent clinical isolates, FC18, C9, 3153A, and WO-1, common laboratory strains, revealed different electrophoretic karyotypes and distinct colonial morphologies on a synthetic medium, similar to spontaneous mutants. The differences of electrophoretic karyotypes observed among clinical isolates resembled the changes found among different kinds of spontaneous morphological mutants. These findings contribute to the understanding of natural karyotypic variability and are in agreement with the hypothesis that chromosomal alterations observed spontaneously under laboratory conditions provide this amictic species with genetic variability in nature.
Assuntos
Candida albicans/genética , Cromossomos Fúngicos/química , Variação Genética/genética , Cariotipagem , Southern Blotting , Aberrações Cromossômicas , Sondas de DNA/genética , DNA Fúngico/genética , DNA Ribossômico/genética , Eletroforese , Mutação/genética , FenótipoRESUMO
Several different repetitive DNA sequences have been isolated from the pathogenic yeast Candida albicans. These include two families of large dispersed repeat sequences (Ca3, Ca24) and a short (23-bp) tandemly repeated element (Ca7) associated with C. albicans telomeres. In addition, a large subtelomeric repeat (WOL17) has been cloned. DNA fragments containing the telomeric repeats are highly variable among different C. albicans strains. We have shown that the Ca3 repeat is relatively more stable and is suitable for use as a species-specific and strain-specific probe for C. albicans.
Assuntos
Candida albicans/genética , Candida/genética , DNA Fúngico/genética , Sequências Repetitivas de Ácido Nucleico , Sequência de Bases , Candida/classificação , Candida/isolamento & purificação , Candida albicans/classificação , Candida albicans/isolamento & purificação , Clonagem Molecular , DNA Fúngico/isolamento & purificação , Biblioteca Gênica , Genes Fúngicos , Humanos , Dados de Sequência Molecular , Mucosa Bucal/microbiologia , Hibridização de Ácido NucleicoRESUMO
At frequencies as high as 1.4%, the pathogenic yeast Candida albicans spontaneously gave rise to morphological mutants exhibiting more than 20 different types of abnormal colonies; approximately two-thirds of the mutants were stable, while the other one-third were unstable and produced mixtures of different colonial forms at very high rates. Abnormal electrophoretic karyotypes were observed for all of the 14 mutants that were examined, indicating that they were associated with different types of single and multiple gross chromosomal rearrangements. Because C. albicans is asexual and does not go through a meiotic cycle, we suggest that the high frequency of chromosomal rearrangements provides a means for genetic variation in this organism.
