Variations of Candida albicans electrophoretic karyotypes

Abstract

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.

Multiple chromosomal and phenotypic changes in spontaneous mutants of Candida albicans

“…Because the brightness of IIIa is lower than expected by comparison with the analogous chromosome in 3 153A (the total amount of DNA loaded in both wells, for 3 153A and for 300 being very close) we cannot regard this pattern to be of aneuploid origin. Taking into account that changes from separated homologues into co-migrating ones are typical for this chromosome Rustchenko-Bulgac, 1991 ; also see Fig. 3), one can conclude that this position on the gel indicates the presence of several different karyotypes in the population.…”

“…Because of instabilities of the strains, the special method of maintenance (-70 "C) and growth of strains was used in these studies (Rustchenko-Bulgac, 1991). The recipes for yeast extract peptone dextrose (YPD) medium, GPA and Lee-Buckley-Campbell (LBC) synthetic medium have been published (Sherman et ul., 1986;Howard et al, 1986).…”

“…The protocol for studying individual colonial morphology was described previously Rustchenko-Bulgac, 1991).…”

“…Initially, such variation was considered to offer reasonable grounds for establishing strain differences that might be used in epidemiological work (Merz, 1990). However, it has become clear that single strains, either fresh isolates or stock cultures, may give rise to mutants with single and multiple alterations in their electrophoretic karyotypes and that the frequency of such spontaneous mutations may be high (Suzuki et al, 1989;Rustchenko-Bulgac et al, 1990 ;Rustchenko-Bulgac, 1991).…”

The use of karyotyping in the systematics of yeasts

“…Medically important Candida species have been extensively studied (Asakura et al 1991;Iwaguchi et al 1990;Mahrous et al 1990;Rustchenko-Bulgac 1991;Snell & Wilkins 1986;Suzuki et al 1988). Chromosomal length polymorphisms have been observed in numerous species, and Rustchenko-Bulgac (1991) considers this phenomenon to be an important mechanism for increasing genetic variability of apomictic species.…”