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| 2. |
- Ahmad, Khadija Mohamed, et al.
(author)
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Genome structure and dynamics of the yeast pathogen Candida glabrata
- 2014
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In: FEMS Yeast Research. - : Oxford University Press (OUP). - 1567-1364 .- 1567-1356. ; 14:4, s. 529-535
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Research review (peer-reviewed)abstract
- The yeast pathogen Candida glabrata is the second most frequent cause of Candida infections. However, from the phylogenetic point of view, C. glabrata is much closer to Saccharomyces cerevisiae than to Candida albicans. Apparently, this yeast has relatively recently changed its life style and become a successful opportunistic pathogen. Recently, several C. glabrata sister-species, among them clinical and environmental isolates, have had their genomes characterized. Also, hundreds of C. glabrata clinical isolates have been characterized for their genomes. These isolates display enormous genomic plasticity. The number and size of chromosomes vary drastically, as well as intra- and inter-chromosomal segmental duplications occur frequently. The observed genome alterations could affect phenotypic properties and thus help to adapt to the highly variable and harsh habitats this yeast finds in different human patients and their tissues. Further genome sequencing of pathogenic isolates will provide a valuable tool to understand the mechanisms behind genome dynamics and help to elucidate the genes contributing to the virulence potential.
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| 3. |
- Ahmad, Khadija Mohamed, et al.
(author)
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Small chromosomes among Danish Candida glabrata isolates originated through different mechanisms.
- 2013
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In: Antonie van Leeuwenhoek. - : Springer Science and Business Media LLC. - 1572-9699 .- 0003-6072. ; 104:1, s. 111-122
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Journal article (peer-reviewed)abstract
- We analyzed 192 strains of the pathogenic yeast Candida glabrata from patients, mainly suffering from systemic infection, at Danish hospitals during 1985-1999. Our analysis showed that these strains were closely related but exhibited large karyotype polymorphism. Nine strains contained small chromosomes, which were smaller than 0.5 Mb. Regarding the year, patient and hospital, these C. glabrata strains had independent origin and the analyzed small chromosomes were structurally not related to each other (i.e. they contained different sets of genes). We suggest that at least two mechanisms could participate in their origin: (i) through a segmental duplication which covered the centromeric region, or (ii) by a translocation event moving a larger chromosome arm to another chromosome that leaves the centromere part with the shorter arm. The first type of small chromosomes carrying duplicated genes exhibited mitotic instability, while the second type, which contained the corresponding genes in only one copy in the genome, was mitotically stable. Apparently, in patients C. glabrata chromosomes are frequently reshuffled resulting in new genetic configurations, including appearance of small chromosomes, and some of these resulting "mutant" strains can have increased fitness in a certain patient "environment".
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| 4. |
- Andersen, Birgit, et al.
(author)
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A recruited protease is involved in catabolism of pyrimidines.
- 2008
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In: Journal of Molecular Biology. - : Elsevier BV. - 1089-8638 .- 0022-2836. ; 379:2, s. 243-250
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Journal article (peer-reviewed)abstract
- In nature, the same biochemical reaction can be catalyzed by enzymes having fundamentally different folds, reaction mechanisms and origins. For example, the third step of the reductive catabolism of pyrimidines, the conversion of N-carbamyl-beta-alanine to beta-alanine, is catalyzed by two beta-alanine synthase (beta ASase, EC 3.5.1.6) subfamilies. We show that the "prototype" eukaryote beta ASases, such as those from Drosophila melanogaster and Arabidopsis thaliana, are relatively efficient in the conversion of N-carbamyl-beta A compared with a representative of fungal beta ASases, the yeast Saccharomyces kluyveri beta ASase, which has a high K(m) value (71 mM). S. kluyveri beta ASase is specifically inhibited by dipeptides and tripeptides, and the apparent K(i) value of glycyl-glycine is in the same range as the substrate K(m). We show that this inhibitor binds to the enzyme active center in a similar way as the substrate. The observed structural similarities and inhibition behavior, as well as the phylogenetic relationship, suggest that the ancestor of the fungal beta ASase was a protease that had modified its profession and become involved in the metabolism of nucleic acid precursors.
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| 5. |
- Andersen, Gorm, et al.
(author)
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A gene duplication led to specialized gamma-aminobutyrate and beta-alanine aminotransferase in yeast
- 2007
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In: The FEBS Journal. - : Wiley. - 1742-464X .- 1742-4658. ; 274:7, s. 1804-1817
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Journal article (peer-reviewed)abstract
- In humans, beta-alanine (BAL) and the neurotransmitter gamma-aminobutyrate (GABA) are transaminated by a single aminotransferase enzyme. Apparently, yeast originally also had a single enzyme, but the corresponding gene was duplicated in the Saccharomyces kluyveri lineage. SkUGA1 encodes a homologue of Saccharomyces cerevisiae GABA aminotransferase, and SkPYD4 encodes an enzyme involved in both BAL and GABA transamination. SkPYD4 and SkUGA1 as well as S. cerevisiae UGA1 and Schizosaccharomyces pombe UGA1 were subcloned, over-expressed and purified. One discontinuous and two continuous coupled assays were used to characterize the substrate specificity and kinetic parameters of the four enzymes. It was found that the cofactor pyridoxal 5'-phosphate is needed for enzymatic activity and alpha-ketoglutarate, and not pyruvate, as the amino group acceptor. SkPyd4p preferentially uses BAL as the amino group donor (V-max/K-m = 0.78 U.mg(-1).mM(-1)), but can also use GABA (V-max/K-m = 0.42 U.mg(-1).mM(-1)), while SkUga1p only uses GABA (V-max/K-m = 4.01 U.mg(-1).mM(-1)). SpUga1p and ScUga1p transaminate only GABA and not BAL. While mammals degrade BAL and GABA with only one enzyme, but in different tissues, S. kluyveri and related yeasts have two different genes/enzymes to apparently 'distinguish' between the two reactions in a single cell. It is likely that upon duplication similar to 200 million years ago, a specialized Uga1p evolved into a 'novel' transaminase enzyme with broader substrate specificity.
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| 6. |
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| 7. |
- Andersen, Gorm, et al.
(author)
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Catabolism of pyrimidines in yeast: A tool to understand degradation of anticancer drugs
- 2006
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In: Nucleosides, Nucleotides & Nucleic Acids. - : Informa UK Limited. - 1525-7770 .- 1532-2335. ; 25:9-11, s. 991-996
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Journal article (peer-reviewed)abstract
- The pyrimidine catabolic pathway is of crucial importance in cancer patients because it is involved in degradation of several chemotherapeutic drugs, such as 5-fluorouracil; it also is important in plants, unicellular eukaryotes, and bacteria for the degradation of pyrimidine-based biocides/antibiotics. During the last decade we have developed a yeast species, Saccharomyces kluyveri, as a model and tool to study the genes and enzymes of the pyrimidine catabolic pathway. In this report, we studied degradation of uracil and its putative degradation products in 38 yeasts and showed that this pathway was present in the ancient yeasts but was lost approximately 100 million years ago in the S. cerevisiae lineage.
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| 8. |
- Becher, Paul G., et al.
(author)
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Chemical signaling and insect attraction is a conserved trait in yeasts
- 2018
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In: Ecology and Evolution. - : Wiley. - 2045-7758. ; , s. 2962-2974
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Journal article (peer-reviewed)abstract
- Yeast volatiles attract insects, which apparently is of mutual benefit, for both yeasts and insects. However, it is unknown whether biosynthesis of metabolites that attract insects is a basic and general trait, or if it is specific for yeasts that live in close association with insects. Our goal was to study chemical insect attractants produced by yeasts that span more than 250 million years of evolutionary history and vastly differ in their metabolism and lifestyle. We bioassayed attraction of the vinegar fly Drosophila melanogaster to odors of phylogenetically and ecologically distinct yeasts grown under controlled conditions. Baker's yeast Saccharomyces cerevisiae, the insect-associated species Candida californica, Pichia kluyveri and Metschnikowia andauensis, wine yeast Dekkera bruxellensis, milk yeast Kluyveromyces lactis, the vertebrate pathogens Candida albicans and Candida glabrata, and oleophilic Yarrowia lipolytica were screened for fly attraction in a wind tunnel. Yeast headspace was chemically analyzed, and co-occurrence of insect attractants in yeasts and flowering plants was investigated through a database search. In yeasts with known genomes, we investigated the occurrence of genes involved in the synthesis of key aroma compounds. Flies were attracted to all nine yeasts studied. The behavioral response to baker's yeast was independent of its growth stage. In addition to Drosophila, we tested the basal hexapod Folsomia candida (Collembola) in a Y-tube assay to the most ancient yeast, Y. lipolytica, which proved that early yeast signals also function on clades older than neopteran insects. Behavioral and chemical data and a search for selected genes of volatile metabolites underline that biosynthesis of chemical signals is found throughout the yeast clade and has been conserved during the evolution of yeast lifestyles. Literature and database reviews corroborate that yeast signals mediate mutualistic interactions between insects and yeasts. Moreover, volatiles emitted by yeasts are commonly found also in flowers and attract many insect species. The collective evidence suggests that the release of volatile signals by yeasts is a widespread and phylogenetically ancient trait, and that insect-yeast communication evolved prior to the emergence of flowering plants. Co-occurrence of the same attractant signals in yeast and flowers suggests that yeast-insect communication may have contributed to the evolution of insect-mediated pollination in flowers.
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| 9. |
- Becher, Paul, et al.
(author)
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Yeast, not fruit volatiles mediate Drosophila melanogaster attraction, oviposition and development
- 2012
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In: Functional Ecology. - : Wiley. - 1365-2435 .- 0269-8463. ; 26:4, s. 822-828
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Journal article (peer-reviewed)abstract
- 1.In nature, the fruit fly Drosophila melanogaster is attracted to fermenting fruit. Micro-organisms like Saccharomyces yeasts growing on fruit occupy a commonly overlooked trophic level between fruit and insects. Although the dietary quality of yeast is well established for D.melanogaster, the individual contribution of fruit and yeast on host finding and reproductive success has not been established. 2.Here, we show that baker's yeast Saccharomyces cerevisiae on its own is sufficient for fruit fly attraction, oviposition and larval development. In contrast, attraction and oviposition were significantly lower if non-fermented grape juice or growth media were used, and yeast-free grapes did not support larval development either. 3.Despite a strong preference for fermented substrates, moderate attraction to and oviposition on unfermented fruit might be adaptive in view of the fly's capacity to vector yeast. 4.Signals emitted by fruit were only of secondary importance because fermenting yeast without fruit induced the same fly behaviour as yeast fermenting on fruit. We identified a synthetic mimic of yeast odour, comprising ethanol, acetic acid, acetoin, 2-phenyl ethanol and 3-methyl-1-butanol, which was as attractive for the fly as fermenting grape juice or fermenting yeast minimal medium. 5.Yeast odours represent the critical signal to establish the flyfruityeast relationship. The traditional plantherbivore niche concept needs to be updated, to accommodate for the role of micro-organisms in insectplant interactions.
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| 10. |
- Beck, Halfdan, et al.
(author)
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Saccharomyces kluyveri as a model organism to study pyrimidine degradation.
- 2008
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In: FEMS Yeast Research. - : Oxford University Press (OUP). - 1567-1364 .- 1567-1356. ; 8:8, s. 1209-1213
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Journal article (peer-reviewed)abstract
- Abstract The yeast Saccharomyces kluyveri (Lachancea kluyveri), a far relative of Saccharomyces cerevisiae, is not a widely studied organism in the laboratory. However, significant contributions to the understanding of nucleic acid precursors degradation in eukaryotes have been made using this model organism. Here we review eukaryotic pyrimidine degradation with emphasis on the contributions made with S. kluyveri and how this increases our understanding of human disease. Additionally, we discuss the possibilities and limitations of this nonconventional yeast as a laboratory organism.
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