Recurrent isolation of an uncommon yeast, Candida pararugosa, from a sarcoma patient.

A yeast was repeatedly isolated from the saliva of a sarcoma patient. A relatively uncommon species, Candida maris, was identified based on the API 20C profile. The yeast species most frequently obtained from the patient's mother and from clinic staff was Candida albicans. A comparison of the yeast obtained from the patient with the type strain of C. maris strongly suggested that the former was not representative of C. maris. Analysis of partial ribosomal DNA sequences of the patient strain and from the type strain of C. maris showed that the two are phylogenetically not closely related. The patient strain was very close to Candida pararugosa, a relatively uncommon asporogenous yeast. DNA reassociation studies among C. pararugosa and patient isolates showed that they were conspecific. We could not determine the source of the yeast infection. This case will alert hospital staff to be aware of the possibility of unexpected environmental microorganisms as causes of infections, colonizations and persistent environmental contamination events in immunocompromised patients.

Identification of a single nuclear localization signal in the C-terminal domain of an Aspergillus DNA topoisomerase II.

DNA topoisomerase II (topo II) is a major nuclear protein that plays an important role in DNA metabolism. We have isolated the gene for topo II ( TOP2) from the filamentous fungus Aspergillus terreus. The deduced amino acid sequence revealed that topo II consists of 1,587 amino acids and has a calculated molecular weight of 180 kDa; the protein expressed in Escherichia coli has an estimated molecular weight of 185 kDa. Expression of topo II polypeptides tagged with yellow fluorescent protein (YFP) in budding yeast suggests that the C-terminal region of the topo II is essential for transport of the fusion protein into the nucleus. The nuclear localization signal (NLS) sequence of topo II is a non-classical bipartite type containing two interdependent, positively charged clusters separated by 15 amino acids. Alanine scanning mutagenesis and deletion analyses showed further that a stretch of 23 amino acid residues (positions 1,234-1,256) is necessary for nuclear import. In addition, we confirmed, using co-immunoprecipitation and two-hybrid analysis, that this non-classical NLS interacts with importin alpha in budding yeast. These results suggest that the fungal topo II NLS is functional in yeast cells.

The expression of the pathogenic yeast Candida albicans catalase gene in response to hydrogen peroxide.

The catalase gene of the pathogenic yeast Candida albicans was cloned and its expression was examined. Activity of the catalase was detected when cells which were in the early logarithmic stage were treated with hydrogen peroxide. Additionally, activity was detected without any treatment to cells in the late logarithmic and stationary phases. When cells were cultured in galactose, glycerol, or ethanol, catalase activity was always observed without the hydrogen peroxide treatment, suggesting that glucose represses the induction of catalase expression. To elucidate the molecular mechanism of catalase expression, the putative gene for catalase and its 5' untranscribed region were cloned. Sequences of the gene and its potential regulatory region revealed several motifs, including a GC box-like element and stress-responsive element (STRE), which could be involved in the transcriptional regulation. Northern analysis showed that hydrogen peroxide and sorbitol activated transcription of the catalase. On the other hand, treatment of glucose strictly repressed the expression of the catalase even when co-treated with hydrogen peroxide. The expression of catalase against treatment with hydrogen peroxide took place very quickly and decreased slowly in the experimental condition adopted here. From these results, we assumed that the expression of the catalase in Candida albicans is regulated by various environmental conditions via motifs for transcriptional activation as in other yeast catalases.

Cloning and characterization of the gene encoding Aspergillus nidulans DNA topoisomerase II.

We have determined the complete nucleotide sequence of a 5544bp genomic DNA fragment from Aspergillus nidulans that encodes DNA topoisomerase II (topo II). It contains a single open reading frame of 4740bp that codes for 1579 amino acid residues with a molecular weight of 178kDa; when expressed in Escherichia coli and Saccharomyces cerevisiae the molecular weight was 180kDa. The gene (TOP2) is divided into three exons. Two introns, 54bp and 60bp in length, are located at nucleotide positions 187 and 3214 respectively. Comparison of the deduced amino acid sequence with other eukaryotic topo II sequences showed a higher degree of identity with other fungal enzymes than the human topo IIalpha. One of monoclonal antibodies raised against human topo II, 6H8, can cross-react with Aspergillus topo II.

Electrophoretic karyotypes of Candida yeasts recurrently isolated from single patients.

Candida strains were isolated repeatedly from single patients during recurrent episodes of Candida infection in a hospital, and their electrophoretic karyotypes were analyzed by pulsed-field gel electrophoresis using CHEF system. When only C. albicans (in 6 patients) or C. glabrata (in 1 patient) were recurrently isolated, their karyotypes from each patient were almost identical to one another, suggesting that they carried single type of the yeast. When multiple species were recovered from single patients (6 cases), the karyotypes of the most frequently recovered yeast species were almost identical with respect to each patient. The electrophoretic karyotype analysis has been proved to be useful for epidemiological studies because the method can tell not only the species identification but also the differences among the strains of the same species.

Electrophoretic karyotypes of isolates of Candida albicans from hospitalized patients.

Electrophoretic karyotypes, namely, the patterns of chromosome-sized DNAs that have been separated by pulsed-field gel electrophoresis, have been reported to vary among different strains of Candida albicans, and can be useful for the delineation of strains. A previous study showed that almost all the electrophoretic karyotypes of isolates of C. albicans collected from the vagina of outpatients were distinguishable from one another. A few of the isolates had a common atypical karyotype and these isolates all had the same phenotype. This report describes the electrophoretic karyotype analysis of isolates from various specimens taken from hospitalized patients. Karyotypes were analysed with respect to the origins of the isolates in terms of two parameters: the number of bands resolved on the gel and a code of four numbers which corresponded to the number of bands that could be separated in each of four sets of chromosome sizes. No specific karyotype was correlated with either the nature of the specimen or the hospital ward to which the patient had been admitted. Most isolates gave a pattern similar to that of FC18 and no atypical karyotypes were found.