Megasatellites: a new class of large tandem repeats discovered in the pathogenic yeast Candida glabrata

Chromosome-level assemblies from diverse clades reveal limited structural and gene content variation in the genome of Candida glabrata

Background

Candida glabrata is an opportunistic yeast pathogen thought to have a large genetic and phenotypic diversity and a highly plastic genome. However, the lack of chromosome-level genome assemblies representing this diversity limits our ability to accurately establish how chromosomal structure and gene content vary across strains.

Results

Here, we expanded publicly available assemblies by using long-read sequencing technologies in twelve diverse strains, obtaining a final set of twenty-one chromosome-level genomes spanning the known C. glabrata diversity. Using comparative approaches, we inferred variation in chromosome structure and determined the pan-genome, including an analysis of the adhesin gene repertoire. Our analysis uncovered four new adhesin orthogroups and inferred a rich ancestral adhesion repertoire, which was subsequently shaped through a still ongoing process of gene loss, gene duplication, and gene conversion.

Conclusions

C. glabrata has a largely stable pan-genome except for a highly variable subset of genes encoding cell wall-associated functions. Adhesin repertoire was established for each strain and showed variability among clades.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12915-022-01412-1.

Megasatellite formation and evolution in vertebrate genes

Since formation of the first proto-eukaryotes, gene repertoire and genome complexity have significantly increased. Among genetic elements responsible for this increase are tandem repeats. Here we describe a genome-wide analysis of large tandem repeats, called megasatellites, in 58 vertebrate genomes. Two bursts occurred, one after the radiation between Agnatha and Gnathostomata fishes and the second one in therian mammals. Megasatellites are enriched in subtelomeric regions and frequently encoded in genes involved in transcription regulation, intracellular trafficking, and cell membrane metabolism, reminiscent of what is observed in fungus genomes. The presence of many introns within young megasatellites suggests that an exon-intron DNA segment is first duplicated and amplified before accumulation of mutations in intronic parts partially erases the megasatellite in such a way that it becomes detectable only in exons. Our results suggest that megasatellite formation and evolution is a dynamic and still ongoing process in vertebrate genomes.

Functional variability in adhesion and flocculation of yeast megasatellite genes

Megasatellites are large tandem repeats found in all fungal genomes but especially abundant in the opportunistic pathogen Candida glabrata. They are encoded in genes involved in cell-cell interactions, either between yeasts or between yeast and human cells. In the present work, we have been using an iterative genetic system to delete several Candida glabrata megasatellite-containing genes and found that 2 of them were positively involved in adhesion to epithelial cells, whereas 3 genes negatively controlled adhesion. Two of the latter, CAGL0B05061g or CAGL0A04851g, were also negative regulators of yeast-to-yeast adhesion, making them central players in controlling Candida glabrata adherence properties. Using a series of synthetic Saccharomyces cerevisiae strains in which the FLO1 megasatellite was replaced by other tandem repeats of similar length but different sequences, we showed that the capacity of a strain to flocculate in liquid culture was unrelated to its capacity to adhere to epithelial cells or to invade agar. Finally, to understand how megasatellites were initially created and subsequently expanded, an experimental evolution system was set up, in which modified yeast strains containing different megasatellite seeds were grown in bioreactors for more than 200 generations and selected for their ability to sediment at the bottom of the culture tube. Several flocculation-positive mutants were isolated. Functionally relevant mutations included general transcription factors as well as a 230-kbp segmental duplication.

Characterization of Awp14, A Novel Cluster III Adhesin Identified in a High Biofilm-Forming Candida glabrata Isolate

Candida glabrata is among the most prevalent causes of candidiasis. Unlike Candida albicans, it is not capable of changing morphology between yeast and hyphal forms but instead has developed other virulence factors. An important feature is its unprecedented large repertoire of predicted cell wall adhesins, which are thought to enable adherence to a variety of surfaces under different conditions. Here, we analyzed the wall proteome of PEU1221, a high biofilm-forming clinical strain isolated from an infected central venous catheter, under biofilm-forming conditions. This isolate shows increased incorporation of putative adhesins, including eight proteins that were not detected in walls of reference strain ATCC 2001, and of which Epa22, Awp14, and Awp2e were identified for the first time. The proteomics data suggest that cluster III adhesin Awp14 is relatively abundant in PEU1221. Phenotypic studies with awp14Δ deletion mutants showed that Awp14 is not responsible for the high biofilm formation of PEU1221 onto polystyrene. However, awp14Δ mutant cells in PEU1221 background showed a slightly diminished binding to chitin and seemed to sediment slightly slower than the parental strain suggesting implication in fungal cell-cell interactions. By structural modeling, we further demonstrate similarity between the ligand-binding domains of cluster III adhesin Awp14 and those of cluster V and VI adhesins. In conclusion, our work confirms the increased incorporation of putative adhesins, such as Awp14, in high biofilm-forming isolates, and contributes to decipher the precise role of these proteins in the establishment of C. glabrata infections.

The Epithelial adhesin 1 tandem repeat region mediates protein display through multiple mechanisms

The pathogenic yeast Candida glabrata is reliant on a suite of cell surface adhesins that play a variety of roles necessary for transmission, establishment and proliferation during infection. One particular adhesin, Epithelial Adhesin 1 [Epa1p], is responsible for binding to host tissue, a process which is essential for fungal propagation. Epa1p structure consists of three domains: an N-terminal intercellular binding domain responsible for epithelial cell binding, a C-terminal GPI anchor for cell wall linkage and a serine/threonine-rich linker domain connecting these terminal domains. The linker domain contains a 40-amino acid tandem repeat region, which we have found to be variable in repeat copy number between isolates from clinical sources. We hypothesized that natural variation in Epa1p repeat copy may modulate protein function. To test this, we recombinantly expressed Epa1p with various repeat copy numbers in S. cerevisiae to determine how differences in repeat copy number affect Epa1p expression, surface display and binding to human epithelial cells. Our data suggest that repeat copy number variation has pleiotropic effects, influencing gene expression, protein surface display and shedding from the cell surface of the Epa1p adhesin. This study serves to demonstrate repeat copy number variation can modulate protein function through a number of mechanisms in order to contribute to pathogenicity of C. glabrata.

Adhesins in Candida glabrata

The human fungal pathogen Candida glabrata is causing more and more problems in hospitals, as this species shows an intrinsic antifungal drug resistance or rapidly becomes resistant when challenged with antifungals. C. glabrata only grows in the yeast form, so it is lacking a yeast-to-hyphae switch, which is one of the main virulence factors of C. albicans. An important virulence factor of C. glabrata is its capacity to strongly adhere to many different substrates. To achieve this, C. glabrata expresses a large number of adhesin-encoding genes and genome comparisons with closely related species, including the non-pathogenic S. cerevisiae, which revealed a correlation between the number of adhesin-encoding genes and pathogenicity. The adhesins are involved in the first steps during an infection; they are the first point of contact with the host. For several of these adhesins, their importance in adherence to different substrates and subsequent biofilm formation was demonstrated in vitro or in vivo. In this review, we provide an overview of the role of C. glabrata adhesins during adhesion and biofilm formation both, under in vitro and in vivo conditions.

Generational distribution of a Candida glabrata population: Resilient old cells prevail, while younger cells dominate in the vulnerable host

Similar to other yeasts, the human pathogen Candida glabrata ages when it undergoes asymmetric, finite cell divisions, which determines its replicative lifespan. We sought to investigate if and how aging changes resilience of C. glabrata populations in the host environment. Our data demonstrate that old C. glabrata are more resistant to hydrogen peroxide and neutrophil killing, whereas young cells adhere better to epithelial cell layers. Consequently, virulence of old compared to younger C. glabrata cells is enhanced in the Galleria mellonella infection model. Electron microscopy images of old C. glabrata cells indicate a marked increase in cell wall thickness. Comparison of transcriptomes of old and young C. glabrata cells reveals differential regulation of ergosterol and Hog pathway associated genes as well as adhesion proteins, and suggests that aging is accompanied by remodeling of the fungal cell wall. Biochemical analysis supports this conclusion as older cells exhibit a qualitatively different lipid composition, leading to the observed increased emergence of fluconazole resistance when grown in the presence of fluconazole selection pressure. Older C. glabrata cells accumulate during murine and human infection, which is statistically unlikely without very strong selection. Therefore, we tested the hypothesis that neutrophils constitute the predominant selection pressure in vivo. When we altered experimentally the selection pressure by antibody-mediated removal of neutrophils, we observed a significantly younger pathogen population in mice. Mathematical modeling confirmed that differential selection of older cells is sufficient to cause the observed demographic shift in the fungal population. Hence our data support the concept that pathogenesis is affected by the generational age distribution of the infecting C. glabrata population in a host. We conclude that replicative aging constitutes an emerging trait, which is selected by the host and may even play an unanticipated role in the transition from a commensal to a pathogen state.

Upregulation of the Adhesin Gene EPA1 Mediated by PDR1 in Candida glabrata Leads to Enhanced Host Colonization

Candida glabrata is an important fungal pathogen in human diseases and is also rapidly acquiring drug resistance. Drug resistance can be mediated by the transcriptional activator PDR1, and this results in the upregulation of multidrug transporters. Intriguingly, this resistance mechanism is associated in C. glabrata with increased virulence in animal models and also with increased adherence to specific host cell types. The C. glabrata adhesin gene EPA1 is a major contributor of virulence and adherence to host cells. Here, we show that EPA1 expression is controlled by PDR1 independently of subtelomeric silencing, a known EPA1 regulation mechanism. Thus, a relationship exists between PDR1, EPA1 expression, and adherence to host cells, which is critical for efficient virulence. Our results demonstrate that acquisition of drug resistance is beneficial for C. glabrata in fungus-host relationships. These findings further highlight the challenges of the therapeutic management of C. glabrata infections in human patients.

Candida glabrata is the second most common Candida species causing disseminated infection, after C. albicans. C. glabrata is intrinsically less susceptible to the widely used azole antifungal drugs and quickly develops secondary resistance. Resistance typically relies on drug efflux with transporters regulated by the transcription factor Pdr1. Gain-of-function (GOF) mutations in PDR1 lead to a hyperactive state and thus efflux transporter upregulation. Our laboratory has characterized a collection of C. glabrata clinical isolates in which azole resistance was found to correlate with increased virulence in vivo. Contributing phenotypes were the evasion of adhesion and phagocytosis by macrophages and an increased adhesion to epithelial cells. These phenotypes were found to be dependent on PDR1 GOF mutation and/or C. glabrata strain background. In the search for the molecular effectors, we found that PDR1 hyperactivity leads to overexpression of specific cell wall adhesins of C. glabrata. Further study revealed that EPA1 regulation, in particular, explained the increase in adherence to epithelial cells. Deleting EPA1 eliminates the increase in adherence in an in vitro model of interaction with epithelial cells. In a murine model of urinary tract infection, PDR1 hyperactivity conferred increased ability to colonize the bladder and kidneys in an EPA1-dependent way. In conclusion, this study establishes a relationship between PDR1 and the regulation of cell wall adhesins, an important virulence attribute of C. glabrata. Furthermore, our data show that PDR1 hyperactivity mediates increased adherence to host epithelial tissues both in vitro and in vivo through upregulation of the adhesin gene EPA1.

IMPORTANCECandida glabrata is an important fungal pathogen in human diseases and is also rapidly acquiring drug resistance. Drug resistance can be mediated by the transcriptional activator PDR1, and this results in the upregulation of multidrug transporters. Intriguingly, this resistance mechanism is associated in C. glabrata with increased virulence in animal models and also with increased adherence to specific host cell types. The C. glabrata adhesin gene EPA1 is a major contributor of virulence and adherence to host cells. Here, we show that EPA1 expression is controlled by PDR1 independently of subtelomeric silencing, a known EPA1 regulation mechanism. Thus, a relationship exists between PDR1, EPA1 expression, and adherence to host cells, which is critical for efficient virulence. Our results demonstrate that acquisition of drug resistance is beneficial for C. glabrata in fungus-host relationships. These findings further highlight the challenges of the therapeutic management of C. glabrata infections in human patients.

Proteomic analysis of hyperadhesive Candida glabrata clinical isolates reveals a core wall proteome and differential incorporation of adhesins

Attachment to human host tissues or abiotic medical devices is a key step in the development of infections by Candida glabrata. The genome of this pathogenic yeast codes for a large number of adhesins, but proteomic work using reference strains has shown incorporation of only few adhesins in the cell wall. By making inventories of the wall proteomes of hyperadhesive clinical isolates and reference strain CBS138 using mass spectrometry, we describe the cell wall proteome of C. glabrata and tested the hypothesis that hyperadhesive isolates display differential incorporation of adhesins. Two clinical strains (PEU382 and PEU427) were selected, which both were hyperadhesive to polystyrene and showed high surface hydrophobicity. Cell wall proteome analysis under biofilm-forming conditions identified a core proteome of about 20 proteins present in all C. glabrata strains. In addition, 12 adhesin-like wall proteins were identified in the hyperadherent strains, including six novel adhesins (Awp8-13) of which only Awp12 was also present in CBS138. We conclude that the hyperadhesive capacity of these two clinical C. glabrata isolates is correlated with increased and differential incorporation of cell wall adhesins. Future studies should elucidate the role of the identified proteins in the establishment of C. glabrata infections.

Genome-wide replication landscape of Candida glabrata

Background

The opportunistic pathogen Candida glabrata is a member of the Saccharomycetaceae yeasts. Like its close relative Saccharomyces cerevisiae, it underwent a whole-genome duplication followed by an extensive loss of genes. Its genome contains a large number of very long tandem repeats, called megasatellites. In order to determine the whole replication program of the C. glabrata genome and its general chromosomal organization, we used deep-sequencing and chromosome conformation capture experiments.

Results

We identified 253 replication fork origins, genome wide. Centromeres, HML and HMR loci, and most histone genes are replicated early, whereas natural chromosomal breakpoints are located in late-replicating regions. In addition, 275 autonomously replicating sequences (ARS) were identified during ARS-capture experiments, and their relative fitness was determined during growth competition. Analysis of ARSs allowed us to identify a 17-bp consensus, similar to the S. cerevisiae ARS consensus sequence but slightly more constrained. Megasatellites are not in close proximity to replication origins or termini. Using chromosome conformation capture, we also show that early origins tend to cluster whereas non-subtelomeric megasatellites do not cluster in the yeast nucleus.

Conclusions

Despite a shorter cell cycle, the C. glabrata replication program shares unexpected striking similarities to S. cerevisiae, in spite of their large evolutionary distance and the presence of highly repetitive large tandem repeats in C. glabrata. No correlation could be found between the replication program and megasatellites, suggesting that their formation and propagation might not be directly caused by replication fork initiation or termination.

Electronic supplementary material

The online version of this article (doi:10.1186/s12915-015-0177-6) contains supplementary material, which is available to authorized users.

Tipping the balance both ways: drug resistance and virulence in Candida glabrata

Among existing fungal pathogens, Candida glabrata is outstanding in its capacity to rapidly develop resistance to currently used antifungal agents. Resistance to the class of azoles, which are still widely used agents, varies in proportion (from 5 to 20%) depending on geographical area. Moreover, resistance to the class of echinocandins, which was introduced in the late 1990s, is rising in several institutions. The recent emergence of isolates with acquired resistance to both classes of agents is a major concern since alternative therapeutic options are scarce. Although considered less pathogenic than C. albicans, C. glabrata has still evolved specific virulence traits enabling its survival and propagation in colonized and infected hosts. Development of drug resistance is usually associated with fitness costs, and this notion is documented across several microbial species. Interestingly, azole resistance in C. glabrata has revealed the opposite. Experimental models of infection showed enhanced virulence of azole-resistant isolates. Moreover, azole resistance could be associated with specific changes in adherence properties to epithelial cells or innate immunity cells (macrophages), both of which contribute to virulence changes. Here we will summarize the current knowledge on C. glabrata drug resistance and also discuss the consequences of drug resistance acquisition on the balance between C. glabrata and its hosts.

One small step for a yeast--microevolution within macrophages renders Candida glabrata hypervirulent due to a single point mutation

Candida glabrata is one of the most common causes of candidemia, a life-threatening, systemic fungal infection, and is surpassed in frequency only by Candida albicans. Major factors contributing to the success of this opportunistic pathogen include its ability to readily acquire resistance to antifungals and to colonize and adapt to many different niches in the human body. Here we addressed the flexibility and adaptability of C. glabrata during interaction with macrophages with a serial passage approach. Continuous co-incubation of C. glabrata with a murine macrophage cell line for over six months resulted in a striking alteration in fungal morphology: The growth form changed from typical spherical yeasts to pseudohyphae-like structures – a phenotype which was stable over several generations without any selective pressure. Transmission electron microscopy and FACS analyses showed that the filamentous-like morphology was accompanied by changes in cell wall architecture. This altered growth form permitted faster escape from macrophages and increased damage of macrophages. In addition, the evolved strain (Evo) showed transiently increased virulence in a systemic mouse infection model, which correlated with increased organ-specific fungal burden and inflammatory response (TNFα and IL-6) in the brain. Similarly, the Evo mutant significantly increased TNFα production in the brain on day 2, which is mirrored in macrophages confronted with the Evo mutant, but not with the parental wild type. Whole genome sequencing of the Evo strain, genetic analyses, targeted gene disruption and a reverse microevolution experiment revealed a single nucleotide exchange in the chitin synthase-encoding CHS2 gene as the sole basis for this phenotypic alteration. A targeted CHS2 mutant with the same SNP showed similar phenotypes as the Evo strain under all experimental conditions tested. These results indicate that microevolutionary processes in host-simulative conditions can elicit adaptations of C. glabrata to distinct host niches and even lead to hypervirulent strains.

Evolution is not limited to making new species emerge and others perish over the millennia. It is also a central force in shorter-term interactions between microbes and hosts. A good example can be found in fungi, which are an underestimated cause of human diseases. Some fungi exist as commensals, and have adapted well to life on human epithelia. But as facultative pathogens, they face a different, hostile environment. We tested the ability of C. glabrata, a pathogen closely related to baker's yeast, to adapt to macrophages. We found that by adaptation, it changed its growth type completely. This allowed the fungus to escape the phagocytes, and increased its virulence in a mouse model. Sequencing the complete genome revealed surprisingly few mutations. Further analyses allowed us to detect the single mutation responsible for the phenotype, and to recreate it in the parental strain. Our work shows that fungi can adapt to immune cells, and that this adaptation can lead to an increased virulence. Since commensals are continuously exposed to host cells, we suggest that this ability could lead to unexpected phenotype changes, including an increase in virulence potential.

Deep conservation of human protein tandem repeats within the eukaryotes

Tandem repeats (TRs) are a major element of protein sequences in all domains of life. They are particularly abundant in mammals, where by conservative estimates one in three proteins contain a TR. High generation-scale duplication and deletion rates were reported for nucleic TR units. However, it is not known whether protein TR units can also be frequently lost or gained providing a source of variation for rapid adaptation of protein function, or alternatively, tend to have conserved TR unit configurations over long evolutionary times. To obtain a systematic picture, we performed a proteome-wide analysis of the mode of evolution for human protein TRs. For this purpose, we propose a novel method for the detection of orthologous TRs based on circular profile hidden Markov models. For all detected TRs, we reconstructed bispecies TR unit phylogenies across 61 eukaryotes ranging from human to yeast. Moreover, we performed additional analyses to correlate functional and structural annotations of human TRs with their mode of evolution. Surprisingly, we find that the vast majority of human TRs are ancient, with TR unit number and order preserved intact since distant speciation events. For example, ≥61% of all human TRs have been strongly conserved at least since the root of all mammals, approximately 300 Ma. Further, we find no human protein TR that shows evidence for strong recent duplications and deletions. The results are in contrast to the high generation-scale mutability of nucleic TRs. Presumably, most protein TRs fold into stable and conserved structures that are indispensable for the function of the TR-containing protein. All of our data and results are available for download from http://www.atgc-montpellier.fr/TRE.

Balanced gene losses, duplications and intensive rearrangements led to an unusual regularly sized genome in Arbutus unedo chloroplasts

Completely sequenced plastomes provide a valuable source of information about the duplication, loss, and transfer events of chloroplast genes and phylogenetic data for resolving relationships among major groups of plants. Moreover, they can also be useful for exploiting chloroplast genetic engineering technology. Ericales account for approximately six per cent of eudicot diversity with 11,545 species from which only three complete plastome sequences are currently available. With the aim of increasing the number of ericalean complete plastome sequences, and to open new perspectives in understanding Mediterranean plant adaptations, a genomic study on the basis of the complete chloroplast genome sequencing of Arbutus unedo and an updated phylogenomic analysis of Asteridae was implemented. The chloroplast genome of A. unedo shows extensive rearrangements but a medium size (150,897 nt) in comparison to most of angiosperms. A number of remarkable distinct features characterize the plastome of A. unedo: five-fold dismissing of the SSC region in relation to most angiosperms; complete loss or pseudogenization of a number of essential genes; duplication of the ndhH-D operon and its location within the two IRs; presence of large tandem repeats located near highly re-arranged regions and pseudogenes. All these features outline the primary evolutionary split between Ericaceae and other ericalean families. The newly sequenced plastome of A. unedo with the available asterid sequences allowed the resolution of some uncertainties in previous phylogenies of Asteridae.

Detection and characterization of megasatellites in orthologous and nonorthologous genes of 21 fungal genomes

Megasatellites are large DNA tandem repeats, originally described in Candida glabrata, in protein-coding genes. Most of the genes in which megasatellites are found are of unknown function. In this work, we extended the search for megasatellites to 20 additional completely sequenced fungal genomes and extracted 216 megasatellites in 203 out of 142,121 genes, corresponding to the most exhaustive description of such genetic elements available today. We show that half of the megasatellites detected encode threonine-rich peptides predicted to be intrinsically disordered, suggesting that they may interact with several partners or serve as flexible linkers. Megasatellite motifs were clustered into several families. Their distribution in fungal genes shows that different motifs are found in orthologous genes and similar motifs are found in unrelated genes, suggesting that megasatellite formation or spreading does not necessarily track the evolution of their host genes. Altogether, these results suggest that megasatellites are created and lost during evolution of fungal genomes, probably sharing similar functions, although their primary sequences are not necessarily conserved.

Adhesins in human fungal pathogens: glue with plenty of stick

Understanding the pathogenesis of an infectious disease is critical for developing new methods to prevent infection and diagnose or cure disease. Adherence of microorganisms to host tissue is a prerequisite for tissue invasion and infection. Fungal cell wall adhesins involved in adherence to host tissue or abiotic medical devices are critical for colonization leading to invasion and damage of host tissue. Here, with a main focus on pathogenic Candida species, we summarize recent progress made in the field of adhesins in human fungal pathogens and underscore the importance of these proteins in establishment of fungal diseases.

Heterogeneous expression of the virulence-related adhesin Epa1 between individual cells and strains of the pathogen Candida glabrata

We investigated the relevance of gene expression heterogeneity to virulence properties of a major fungal pathogen, Candida glabrata. The organism's key virulence-associated factors include glycosylphosphatidylinositol-anchored adhesins, encoded subtelomerically by the EPA gene family. Individual-cell analyses of expression revealed very striking heterogeneity for Epa1, an adhesin that mediates ∼95% of adherence to epithelial cells in vitro. The heterogeneity in Epa1 was markedly greater than that known for other yeast genes. Sorted cells expressing high or low levels of Epa1 exhibited high and low adherence to epithelial cells, indicating a link between gene expression noise and potential virulence. The phenotypes of sorted subpopulations reverted to mixed phenotypes within a few generations. Variation in single-cell Epa1 protein and mRNA levels was correlated, consistent with transcriptional regulation of heterogeneity. Sir-dependent transcriptional silencing was the primary mechanism driving heterogeneous Epa1 expression in C. glabrata BG2, but not in CBS138 (ATCC 2001). Inefficient silencing in the latter strain was not due to a difference in EPA1 sequence or (sub)telomere length and was overcome by ectopic SIR3 expression. Moreover, differences between strains in the silencing dependence of EPA1 expression were evident across a range of clinical isolates, with heterogeneity being the greatest in strains where EPA1 was subject to silencing. The study shows how heterogeneity can impact the virulence-related properties of C. glabrata cell populations, with potential implications for microbial pathogenesis more broadly.

Candida glabrata Pwp7p and Aed1p are required for adherence to human endothelial cells

Candida glabrata owes its success as a pathogen, in part, to a large repertoire of adhesins present on the cell surface. Our current knowledge of C. glabrata adhesins and their role in the interaction between host and pathogen is limited to work with only a single family of epithelial adhesins (Epa proteins). Here, we report on the identification and characterization of a family of glycosylphosphatidylinositol-anchored cell wall proteins in C. glabrata. These proteins are absent in both Saccharomyces cerevisiae and Candida albicans, suggesting that C. glabrata has evolved different mechanism(s) for interaction with host cells. In the current study, we present data on the characterization of Pwp7p (PA14 domain containing Wall Protein) and Aed1p (Adherence to Endothelial cells) of this family in the interaction of C. glabrata with human umbilical vein endothelial cells. The deletion of C. glabrata genes PWP7 and AED1 results in a significant reduction in adherence to endothelial cells compared with the wild-type parent. These data indicate that C. glabrata utilizes these proteins for adherence to endothelial cells in vitro.

From Saccharomyces cerevisiae to Candida glabratain a few easy steps: important adaptations for an opportunistic pathogen

The opportunistic human fungal pathogen Candida glabrata is closely related to Saccharomyces cerevisiae, yet it has evolved to survive within mammalian hosts. Which traits help C. glabrata to adapt to this different environment? Which specific responses are crucial for its survival in the host? The main differences seem to include an extended repertoire of adhesin genes, high drug resistance, an enhanced ability to sustain prolonged starvation and adaptations of the transcriptional wiring of key stress response genes. Here, we discuss the properties of C. glabrata with a focus on the differences to related fungi.

Dynamic evolution of megasatellites in yeasts

Megasatellites are a new family of long tandem repeats, recently discovered in the yeast Candida glabrata. Compared to shorter tandem repeats, such as minisatellites, megasatellite motifs range in size from 135 to more than 300 bp, and allow calculation of evolutionary distances between individual motifs. Using divergence based on nucleotide substitutions among similar motifs, we determined the smallest distance between two motifs, allowing their subsequent clustering. Motifs belonging to the same cluster are recurrently found in different megasatellites located on different chromosomes, showing transfer of genetic information between megasatellites. In comparison, evolution of the few similar tandem repeats in Saccharomyces cerevisiae FLO genes mainly involves subtelomeric homologous recombination. We estimated selective constraints acting on megasatellite motifs and their host genes, and found that motifs are under strong purifying selection. Surprisingly, motifs inserted within pseudogenes are also under purifying selection, whereas the pseudogenes themselves evolve neutrally. We propose that megasatellite motifs propagate by a combination of three different molecular mechanisms: (i) gene duplication, (ii) ectopic homologous recombination and (iii) transfer of motifs from one megasatellite to another one. These mechanisms actively cooperate to create new megasatellites, that may play an important role in the adaptation of Candida glabrata to its human host.