Sequence and analysis of the genome of the pathogenic yeast Candida orthopsilosis

Genomic factors shape carbon and nitrogen metabolic niche breadth across Saccharomycotina yeasts

Organisms exhibit extensive variation in ecological niche breadth, from very narrow (specialists) to very broad (generalists). Two general paradigms have been proposed to explain this variation: (i) trade-offs between performance efficiency and breadth and (ii) the joint influence of extrinsic (environmental) and intrinsic (genomic) factors. We assembled genomic, metabolic, and ecological data from nearly all known species of the ancient fungal subphylum Saccharomycotina (1154 yeast strains from 1051 species), grown in 24 different environmental conditions, to examine niche breadth evolution. We found that large differences in the breadth of carbon utilization traits between yeasts stem from intrinsic differences in genes encoding specific metabolic pathways, but we found limited evidence for trade-offs. These comprehensive data argue that intrinsic factors shape niche breadth variation in microbes.

Origin of fungal hybrids with pathogenic potential from warm seawater environments

Hybridisation is a common event in yeasts often leading to genomic variability and adaptation. The yeast Candida orthopsilosis is a human-associated opportunistic pathogen belonging to the Candida parapsilosis species complex. Most C. orthopsilosis clinical isolates are hybrids resulting from at least four independent crosses between two parental lineages, of which only one has been identified. The rare presence or total absence of parentals amongst clinical isolates is hypothesised to be a consequence of a reduced pathogenicity with respect to their hybrids. Here, we sequence and analyse the genomes of environmental C. orthopsilosis strains isolated from warm marine ecosystems. We find that a majority of environmental isolates are hybrids, phylogenetically closely related to hybrid clinical isolates. Furthermore, we identify the missing parental lineage, thus providing a more complete overview of the genomic evolution of this species. Additionally, we discover phenotypic differences between the two parental lineages, as well as between parents and hybrids, under conditions relevant for pathogenesis. Our results suggest a marine origin of C. orthopsilosis hybrids, with intrinsic pathogenic potential, and pave the way to identify pre-existing environmental adaptations that rendered hybrids more prone than parental lineages to colonise and infect the mammalian host.

Evolution of loss of heterozygosity patterns in hybrid genomes of Candida yeast pathogens

BACKGROUND

Hybrids are chimeric organisms with highly plastic heterozygous genomes that may confer unique traits enabling the adaptation to new environments. However, most evolutionary theory frameworks predict that the high levels of genetic heterozygosity present in hybrids from divergent parents are likely to result in numerous deleterious epistatic interactions. Under this scenario, selection is expected to favor recombination events resulting in loss of heterozygosity (LOH) affecting genes involved in such negative interactions. Nevertheless, it is so far unknown whether this phenomenon actually drives genomic evolution in natural populations of hybrids. To determine the balance between selection and drift in the evolution of LOH patterns in natural yeast hybrids, we analyzed the genomic sequences from fifty-five hybrid strains of the pathogenic yeasts Candida orthopsilosis and Candida metapsilosis, which derived from at least six distinct natural hybridization events.

RESULTS

We found that, although LOH patterns in independent hybrid clades share some level of convergence that would not be expected from random occurrence, there is an apparent lack of strong functional selection. Moreover, while mitosis is associated with a limited number of inter-homeologous chromosome recombinations in these genomes, induced DNA breaks seem to increase the LOH rate. We also found that LOH does not accumulate linearly with time in these hybrids. Furthermore, some C. orthopsilosis hybrids present LOH patterns compatible with footprints of meiotic recombination. These meiotic-like patterns are at odds with a lack of evidence of sexual recombination and with our inability to experimentally induce sporulation in these hybrids.

CONCLUSIONS

Our results suggest that genetic drift is the prevailing force shaping LOH patterns in these hybrid genomes. Moreover, the observed LOH patterns suggest that these are likely not the result of continuous accumulation of sporadic events-as expected by mitotic repair of rare chromosomal breaks-but rather of acute episodes involving many LOH events in a short period of time.

Genome analysis of five recently described species of the CUG-Ser clade uncovers Candida theae as a new hybrid lineage with pathogenic potential in the Candida parapsilosis species complex

Candida parapsilosis species complex comprises three important pathogenic species: Candida parapsilosis sensu stricto, Candida orthopsilosis and Candida metapsilosis. The majority of C. orthopsilosis and all C. metapsilosis isolates sequenced thus far are hybrids, and most of the parental lineages remain unidentified. This led to the hypothesis that hybrids with pathogenic potential were formed by the hybridization of non-pathogenic lineages that thrive in the environment. In a search for the missing hybrid parentals, and aiming to get a better understanding of the evolution of the species complex, we sequenced, assembled and analysed the genome of five close relatives isolated from the environment: Candida jiufengensis, Candida pseudojiufengensis, Candida oxycetoniae, Candida margitis and Candida theae. We found that the linear conformation of mitochondrial genomes in Candida species emerged multiple times independently. Furthermore, our analyses discarded the possible involvement of these species in the mentioned hybridizations, but identified C. theae as an additional hybrid in the species complex. Importantly, C. theae was recently associated with a case of infection, and we also uncovered the hybrid nature of this clinical isolate. Altogether, our results reinforce the hypothesis that hybridization is widespread among Candida species, and potentially contributes to the emergence of lineages with opportunistic pathogenic behaviour.

Identification of a novel Candida metapsilosis isolate reveals multiple hybridization events

Candida metapsilosis is a member of the Candida parapsilosis species complex, a group of opportunistic human pathogens. Of all the members of this complex, C. metapsilosis is the least virulent, and accounts for a small proportion of invasive Candida infections. Previous studies established that all C. metapsilosis isolates are hybrids, originating from a single hybridization event between two lineages, parent A and parent B. Here, we use MinION and Illumina sequencing to characterize a C. metapsilosis isolate that originated from a separate hybridization. One of the parents of the new isolate is very closely related to parent A. However, the other parent (parent C) is not the same as parent B. Unlike C. metapsilosis AB isolates, the C. metapsilosis AC isolate has not undergone introgression at the mating type-like locus. In addition, the A and C haplotypes are not fully collinear. The C. metapsilosis AC isolate has undergone loss of heterozygosity with a preference for haplotype A, indicating that this isolate is in the early stages of genome stabilization.

Using Genomics to Shape the Definition of the Agglutinin-Like Sequence (ALS) Family in the Saccharomycetales

The Candida albicans agglutinin-like sequence (ALS) family is studied because of its contribution to cell adhesion, fungal colonization, and polymicrobial biofilm formation. The goal of this work was to derive an accurate census and sequence for ALS genes in pathogenic yeasts and other closely related species, while probing the boundaries of the ALS family within the Order Saccharomycetales. Bioinformatic methods were combined with laboratory experimentation to characterize 47 novel ALS loci from 8 fungal species. AlphaFold predictions suggested the presence of a conserved N-terminal adhesive domain (NT-Als) structure in all Als proteins reported to date, as well as in S. cerevisiae alpha-agglutinin (Sag1). Lodderomyces elongisporus, Meyerozyma guilliermondii, and Scheffersomyces stipitis were notable because each species had genes with C. albicans ALS features, as well as at least one that encoded a Sag1-like protein. Detection of recombination events between the ALS family and gene families encoding other cell-surface proteins such as Iff/Hyr and Flo suggest widespread domain swapping with the potential to create cell-surface diversity among yeast species. Results from the analysis also revealed subtelomeric ALS genes, ALS pseudogenes, and the potential for yeast species to secrete their own soluble adhesion inhibitors. Information presented here supports the inclusion of SAG1 in the ALS family and yields many experimental hypotheses to pursue to further reveal the nature of the ALS family.

Opportunistic yeast pathogen Candida spp.: Secreted and membrane-bound virulence factors

Candidiasis is a fungal infection caused by Candida spp. especially Candida albicans, C. glabrata, C. parapsilosis and C. tropicalis. Although the medicinal therapeutic strategies have rapidly improved, the mortality rate due to candidiasis has continuously increased. The secreted and membrane-bound virulence factors (VFs) are responsible for fungal invasion, damage and translocation through the host enterocytes besides the evasion from host immune system. VFs such as agglutinin-like sequences (Als), heat shock protein 70, phospholipases, secreted aspartyl proteinases (Sap), lipases, enolases and phytases are mostly hydrolases which degrade the enterocyte membrane components except for candidalysin, the VF acts as a peptide toxin to induce necrotic cell lysis. To date, structural studies of the VFs remain underexplored, hindering their functional analyses. Among the VFs, only secreted aspartyl proteinases and agglutinin-like sequences have their structures deposited in Protein Data Bank (PDB). Therefore, this review scrutinizes the mechanisms of these VFs by discussing the VF-deficient studies of several Candida spp. and their abilities to produce these VFs. Nonetheless, their latest reported sequential and structural analyses are discussed to impart a wider perception of the host-pathogen interactions and potential vaccine or antifungal drug targets. This review signifies that more VFs structural investigations and mining in the emerging Candida spp. are required to decipher their pathogenicity and virulence mechanisms compared to the prominent C. albicans.

LAY ABSTRACT

Candida virulence factors (VFs) including mainly enzymes and proteins play vital roles in breaching the human intestinal barrier and causing deadly candidiasis. Limited VFs' structural studies hinder deeper comprehension of their mechanisms and thus the design of vaccines and antifungal drugs against fungal infections.

Genetic Manipulation as a Tool to Unravel Candida parapsilosis Species Complex Virulence and Drug Resistance: State of the Art

An increase in the rate of isolation of Candida parapsilosis in the past decade, as well as increased identification of azole-resistant strains are concerning, and require better understanding of virulence-like factors and drug-resistant traits of these species. In this regard, the present review “draws a line” on the information acquired, thus far, on virulence determinants and molecular mechanisms of antifungal resistance in these opportunistic pathogens, mainly derived from genetic manipulation studies. This will provide better focus on where we stand in our understanding of the C. parapsilosis species complex–host interaction, and how far we are from defining potential novel targets or therapeutic strategies—key factors to pave the way for a more tailored management of fungal infections caused by these fungal pathogens.

Role of CpALS4790 and CpALS0660 in Candida parapsilosis Virulence: Evidence from a Murine Model of Vaginal Candidiasis

The Candida parapsilosis genome encodes for five agglutinin-like sequence (Als) cell-wall glycoproteins involved in adhesion to biotic and abiotic surfaces. The work presented here is aimed at analyzing the role of the two still uncharacterized ALS genes in C. parapsilosis, CpALS4790 and CpALS0660, by the generation and characterization of CpALS4790 and CpALS066 single mutant strains. Phenotypic characterization showed that both mutant strains behaved as the parental wild type strain regarding growth rate in liquid/solid media supplemented with cell-wall perturbing agents, and in the ability to produce pseudohyphae. Interestingly, the ability of the CpALS0660 null mutant to adhere to human buccal epithelial cells (HBECs) was not altered when compared with the wild-type strain, whereas deletion of CpALS4790 led to a significant loss of the adhesion capability. RT-qPCR analysis performed on the mutant strains in co-incubation with HBECs did not highlight significant changes in the expression levels of others ALS genes. In vivo experiments in a murine model of vaginal candidiasis indicated a significant reduction in CFUs recovered from BALB/C mice infected with each mutant strain in comparison to those infected with the wild type strain, confirming the involvement of CpAls4790 and CpAls5600 proteins in C. parapsilosis vaginal candidiasis in mice.

Polymorphic centromere locations in the pathogenic yeast Candida parapsilosis

Centromeres pose an evolutionary paradox: strongly conserved in function but rapidly changing in sequence and structure. However, in the absence of damage, centromere locations are usually conserved within a species. We report here that isolates of the pathogenic yeast species Candida parapsilosis show within-species polymorphism for the location of centromeres on two of its eight chromosomes. Its old centromeres have an inverted-repeat (IR) structure, whereas its new centromeres have no obvious structural features but are located within 30 kb of the old site. Centromeres can therefore move naturally from one chromosomal site to another, apparently spontaneously and in the absence of any significant changes in DNA sequence. Our observations are consistent with a model in which all centromeres are genetically determined, such as by the presence of short or long IRs or by the ability to form cruciforms. We also find that centromeres have been hotspots for genomic rearrangements in the C. parapsilosis clade.

The Transcriptional Aftermath in Two Independently Formed Hybrids of the Opportunistic Pathogen Candida orthopsilosis

How new pathogens emerge is an important question that remains largely unanswered. Some emerging yeast pathogens are hybrids originated through the crossing of two different species, but how hybridization contributes to higher virulence is unclear. Here, we show that hybrids selectively retain gene regulation plasticity inherited from the two parents and that this plasticity affects genes involved in virulence.

Interspecific hybridization can drive evolutionary adaptation to novel environments. The Saccharomycotina clade of budding yeasts includes many hybrid lineages, and hybridization has been proposed as a source for new pathogenic species. Candida orthopsilosis is an emerging opportunistic pathogen for which most clinical isolates are hybrids, each derived from one of at least four independent crosses between the same two parental lineages. To gain insight into the transcriptomic aftermath of hybridization in these pathogens, we analyzed allele-specific gene expression in two independently formed hybrid strains and in a homozygous strain representative of one parental lineage. Our results show that the effect of hybridization on overall gene expression is rather limited, affecting ∼4% of the genes studied. However, we identified a larger effect in terms of imbalanced allelic expression, affecting ∼9.5% of the heterozygous genes in the hybrids. This effect was larger in the hybrid with more extensive loss of heterozygosity, which may indicate a tendency to avoid loss of heterozygosity in these genes. Consistently, the number of shared genes with allele-specific expression in the two independently formed hybrids was higher than random expectation, suggesting selective retention. Some of the imbalanced genes have functions related to pathogenicity, including zinc transport and superoxide dismutase activities. While it remains unclear whether the observed imbalanced genes play a role in virulence, our results suggest that differences in allele-specific expression may add an additional layer of phenotypic plasticity to traits related to virulence in C. orthopsilosis hybrids.

IMPORTANCE How new pathogens emerge is an important question that remains largely unanswered. Some emerging yeast pathogens are hybrids originated through the crossing of two different species, but how hybridization contributes to higher virulence is unclear. Here, we show that hybrids selectively retain gene regulation plasticity inherited from the two parents and that this plasticity affects genes involved in virulence.

Genomic evidence for a hybrid origin of the yeast opportunistic pathogen Candida albicans

Background

Opportunistic yeast pathogens of the genus Candida are an important medical problem. Candida albicans, the most prevalent Candida species, is a natural commensal of humans that can adopt a pathogenic behavior. This species is highly heterozygous and cannot undergo meiosis, adopting instead a parasexual cycle that increases genetic variability and potentially leads to advantages under stress conditions. However, the origin of C. albicans heterozygosity is unknown, and we hypothesize that it could result from ancestral hybridization. We tested this idea by analyzing available genomes of C. albicans isolates and comparing them to those of hybrid and non-hybrid strains of other Candida species.

Results

Our results show compelling evidence that C. albicans is an evolved hybrid. The genomic patterns observed in C. albicans are similar to those of other hybrids such as Candida orthopsilosis MCO456 and Candida inconspicua, suggesting that it also descends from a hybrid of two divergent lineages. Our analysis indicates that most of the divergence between haplotypes in C. albicans heterozygous blocks was already present in a putative heterozygous ancestor, with an estimated 2.8% divergence between homeologous chromosomes. The levels and patterns of ancestral heterozygosity found cannot be fully explained under the paradigm of vertical evolution and are not consistent with continuous gene flux arising from lineage-specific events of admixture.

Conclusions

Although the inferred level of sequence divergence between the putative parental lineages (2.8%) is not clearly beyond current species boundaries in Saccharomycotina, we show here that all analyzed C. albicans strains derive from a single hybrid ancestor and diverged by extensive loss of heterozygosity. This finding has important implications for our understanding of C. albicans evolution, including the loss of the sexual cycle, the origin of the association with humans, and the evolution of virulence traits.

Induction of aquaporin 4-reactive antibodies in Lewis rats immunized with aquaporin 4 mimotopes

Most cases of neuromyelitis optica spectrum disorders (NMOSD) harbor pathogenic autoantibodies against the water channel aquaporin 4 (AQP4). Binding of these antibodies to AQP4 on astrocytes initiates damage to these cells, which culminates in the formation of large tissue destructive lesions in the central nervous system (CNS). Consequently, untreated patients may become permanently blind or paralyzed. Studies on the induction and breakage of tolerance to AQP4 could be of great benefit for NMOSD patients. So far, however, all attempts to create suitable animal models by active sensitization have failed. We addressed this challenge and identified peptides, which mimic the conformational AQP4 epitopes recognized by pathogenic antibodies of NMOSD patients. Here we show that these mimotopes can induce the production of AQP4-reactive antibodies in Lewis rats. Hence, our results provide a conceptual framework for the formation of such antibodies in NMOSD patients, and aid to improve immunization strategies for the creation of animal models suitable for tolerance studies in this devastating disease.

High-resolution mycobiota analysis reveals dynamic intestinal translocation preceding invasive candidiasis

The intestinal microbiota is a complex community of bacteria, archaea, viruses, protists and fungi^1,2. While the composition of bacterial constituents has been linked to immune homeostasis and to infectious susceptibility^3–7, the role of non-bacterial constituents and of cross-kingdom microbial interactions in these processes is poorly understood^2,8. Fungi represent a major cause of infectious morbidity and mortality in immune-compromised individuals, though the relationship of intestinal fungi (i.e., the mycobiota) with fungal bloodstream infections (BSI) remains undefined⁹. We integrated an optimized bioinformatics pipeline with high-resolution mycobiota sequencing and comparative genomic analyses of fecal and blood specimens from recipients of allogeneic hematopoietic cell transplant (allo-HCT). Patients with Candida BSI experienced a prior marked intestinal expansion of pathogenic Candida species; this expansion consisted of a complex dynamic between multiple species and subspecies with a stochastic translocation pattern into the bloodstream. The intestinal expansion of pathogenic Candida species was associated with a significant loss in bacterial burden and diversity, particularly in the anaerobes. Thus, simultaneous analysis of intestinal fungi and bacteria identifies dysbiosis states across kingdoms that may promote fungal translocation and facilitate invasive disease. These findings support microbiota-driven approaches to identify patients at risk for fungal BSI for pre-emptive therapeutic intervention.

A CRISPR/Cas9-based strategy to simultaneously inactivate the entire ALS gene family in Candida orthopsilosis

Aim: In this study, the CRISPR gene-editing approach was used to simultaneously inactivate all three members of the ALS gene family in the opportunistic pathogen Candida orthopsilosis. Materials & methods: Using a single gRNA and repair template, CRISPR-edited clones were successfully generated in a one-step process in both C. orthopsilosis reference and clinical strains. Results: The phenotypic characterization of the ALS triple-edited strains revealed no impact on growth in liquid or solid media. However, pseudohyphal formation and the ability to adhere to human buccal epithelial cells were significantly decreased in triple-edited clones. Conclusion: Our CRISPR/Cas9 system is a powerful tool for simultaneous editing of fungal gene families, which greatly accelerates the generation of multiple gene-edited Candida strains. Data deposition: Nucleotide sequence data are available in the GenBank databases under the accession numbers MK875971, MK875972, MK875973, MK875974, MK875975, MK875976, MK875977.

CoERG11 A395T mutation confers azole resistance in Candida orthopsilosis clinical isolates

Background

Candida orthopsilosis is a human fungal pathogen responsible for a wide spectrum of symptomatic infections. Evidence suggests that C. orthopsilosis is mainly susceptible to azoles, the most extensively used antifungals for treatment of these infections. However, fluconazole-resistant clinical isolates are reported.

Objectives

This study evaluated the contribution of a single amino acid substitution in the azole target CoErg11 to the development of azole resistance in C. orthopsilosis.

Methods

C. orthopsilosis clinical isolates (n = 40) were tested for their susceptibility to azoles and their CoERG11 genes were sequenced. We used a SAT1 flipper-driven transformation to integrate a mutated CoERG11 allele in the genetic background of a fluconazole-susceptible isolate.

Results

Susceptibility testing revealed that 16 of 40 C. orthopsilosis clinical isolates were resistant to fluconazole and to at least one other azole. We identified an A395T mutation in the CoERG11 coding sequence of azole-resistant isolates only that resulted in the non-synonymous amino acid substitution Y132F. The SAT1 flipper cassette strategy led to the creation of C. orthopsilosis mutants that carried the A395T mutation in one or both CoERG11 alleles (heterozygous or homozygous mutant, respectively) in an azole-susceptible genetic background. We tested mutant strains for azole susceptibility and for hot-spot locus heterozygosity. Both the heterozygous and the homozygous mutant strains exhibited an azole-resistant phenotype.

Conclusions

To the best of our knowledge, these findings provide the first evidence that the CoErg11 Y132F substitution confers multi-azole resistance in C. orthopsilosis.

Correlating Genotype and Phenotype in the Asexual Yeast Candida orthopsilosis Implicates ZCF29 in Sensitivity to Caffeine

Candida orthopsilosis is diploid asexual yeast that causes human disease. Most C. orthopsilosis isolates arose from at least four separate hybridizations between related, but not identical, parents. Here, we used population genomics data to correlate genotypic and phenotypic variation in 28 C. orthopsilosis isolates. We used cosine similarity scores to identify 65 variants with potential high-impact (deleterious effects) that correlated with specific phenotypes. Of these, 19 were Single Nucleotide Polymorphisms (SNPs) that changed stop or start codons, or splice sites. One variant resulted in a premature stop codon in both alleles of the gene ZCF29 in C. orthopsilosis isolate 185, which correlated with sensitivity to nystatin and caffeine. We used CRISPR-Cas9 editing to introduce this polymorphism into two resistant C. orthopsilosis isolates. Introducing the stop codon resulted in sensitivity to caffeine and to ketoconazole, but not to nystatin. Our analysis shows that it is possible to associate genomic variants with phenotype in asexual Candida species, but that only a small amount of genomic variation can be easily explored.

Molecular Identification, Genotypic Diversity, Antifungal Susceptibility, and Clinical Outcomes of Infections Caused by Clinically Underrated Yeasts, Candida orthopsilosis, and Candida metapsilosis: An Iranian Multicenter Study (2014-2019)

Despite the increasing occurrence of Candida orthopsilosis and Candida metapsilosis in clinical settings, little is known about their microbiological and clinical properties. Herein, we conducted a national retrospective study (2014–2019) from multiple centers in Iran. Among the 1,770 Candida isolates collected, we identified 600 Candida parapsilosis species complex isolates. Isolate identification was performed by 9-plex PCR, matrix-assisted laser desorption-time of flight mass spectrometry (MALDI-TOF MS), and rDNA sequencing, and antifungal susceptibility testing (AFST) followed CLSI M27-A3/S4; genotyping was performed by amplified fragment length polymorphism (AFLP) analysis; and clinical information was mined. Thirty-one isolates of C. orthopsilosis from various clinical sources, one mixed sample (blood) concurrently containing C. orthopsilosis and C. parapsilosis and one isolate of C. metapsilosis from a nail sample were identified. Although both 9-plex PCR and MALDI-TOF successfully identified all isolates, only 9-plex PCR could identify the agents in a mixed sample. For the C. orthopsilosis isolates, resistance (non-wild type) was noted only for itraconazole (n = 4; 12.5%). Anidulafungin and fluconazole showed the highest and voriconazole had the lowest geometric mean values. AFLP analysis showed three main and four minor genotypes. Interestingly, 90% of nail isolates clustered with 80% of the blood isolates within two clusters, and four blood isolates recovered from four patients admitted to a hospital clustered into two genotypes and showed a high degree of similarity (>99.2%), which suggests that C. orthopsilosis disseminates horizontally. Supported by our data and published case studies, C. orthopsilosis and C. metapsilosis can be linked to challenging clinical failures, and successful outcomes are not always mirrored by in vitro susceptibility. Accordingly, conducting nationwide studies may provide more comprehensive data, which is required for a better prognosis and clinical management of patients.

Agglutinin-Like Sequence (ALS) Genes in the Candida parapsilosis Species Complex: Blurring the Boundaries Between Gene Families That Encode Cell-Wall Proteins

The agglutinin-like sequence (Als) proteins are best-characterized in Candida albicans and known for their role in adhesion of the fungal cell to host and abiotic surfaces. ALS sequences are often misassembled in whole-genome sequence data because each species has multiple ALS loci that contain similar sequences, most notably tandem copies of highly conserved repeated sequences. The Candida parapsilosis species complex includes Candida parapsilosis, Candida orthopsilosis, and Candida metapsilosis, three distinct but closely related species. Using publicly available genome resources, de novo genome assemblies, and laboratory experimentation including Sanger sequencing, five ALS genes were characterized in C. parapsilosis strain CDC317, three in C. orthopsilosis strain 90-125, and four in C. metapsilosis strain ATCC 96143. The newly characterized ALS genes shared similar features with the well-known C. albicans ALS family, but also displayed unique attributes such as novel short, imperfect repeat sequences that were found in other genes encoding fungal cell-wall proteins. Evidence of recombination between ALS sequences and other genes was most obvious in CmALS2265, which had the 5' end of an ALS gene and the repeated sequences and 3' end from the IFF/HYR family. Together, these results blur the boundaries between the fungal cell-wall families that were defined in C. albicans. TaqMan assays were used to quantify relative expression for each ALS gene. Some measurements were complicated by the assay location within the ALS gene. Considerable variation was noted in relative gene expression for isolates of the same species. Overall, however, there was a trend toward higher relative gene expression in saturated cultures rather than younger cultures. This work provides a complete description of the ALS genes in the C. parapsilosis species complex and a toolkit that promotes further investigations into the role of the Als proteins in host-fungal interactions.

Characterization of the Candida orthopsilosis agglutinin-like sequence (ALS) genes

Agglutinin like sequence (Als) cell-wall proteins play a key role in adhesion and virulence of Candida species. Compared to the well-characterized Candida albicans ALS genes, little is known about ALS genes in the Candida parapsilosis species complex. Three incomplete ALS genes were identified in the genome sequence for Candida orthopsilosis strain 90–125 (GenBank assembly ASM31587v1): CORT0C04210 (named CoALS4210), CORT0C04220 (CoALS4220) and CORT0B00800 (CoALS800). To complete the gene sequences, new data were derived from strain 90–125 using Illumina (short-read) and Oxford Nanopore (long-read) methods. Long-read sequencing analysis confirmed the presence of 3 ALS genes in C. orthopsilosis 90–125 and resolved the gaps located in repetitive regions of CoALS800 and CoALS4220. In the new genome assembly (GenBank PQBP00000000), the CoALS4210 sequence was slightly longer than in the original assembly. C. orthopsilosis Als proteins encoded features well-known in C. albicans Als proteins such as a secretory signal peptide, N-terminal domain with a peptide-binding cavity, amyloid-forming region, repeated sequences, and a C-terminal site for glycosylphosphatidylinositol anchor addition that, in yeast, suggest localization of the proteins in the cell wall. CoAls4210 and CoAls800 lacked the classic C. albicans Als tandem repeats, instead featuring short, imperfect repeats with consensus motifs such as SSSEPP and GSGN. Quantitative RT-PCR showed differential regulation of CoALS genes by growth stage in six genetically diverse C. orthopsilosis clinical isolates, which also exhibited length variation in the ALS alleles, and strain-specific gene expression patterns. Overall, long-read DNA sequencing methodology was instrumental in generating an accurate assembly of CoALS genes, thus revealing their unconventional features and first insights into their allelic variability within C. orthopsilosis clinical isolates.

Candida parapsilosis: from Genes to the Bedside

Patients with suppressed immunity are at the highest risk for hospital-acquired infections. Among these, invasive candidiasis is the most prevalent systemic fungal nosocomial infection. Over recent decades, the combined prevalence of non-albicans Candida species outranked Candida albicans infections in several geographical regions worldwide, highlighting the need to understand their pathobiology in order to develop effective treatment and to prevent future outbreaks. Candida parapsilosis is the second or third most frequently isolated Candida species from patients. Besides being highly prevalent, its biology differs markedly from that of C. albicans, which may be associated with C. parapsilosis' increased incidence. Differences in virulence, regulatory and antifungal drug resistance mechanisms, and the patient groups at risk indicate that conclusions drawn from C. albicans pathobiology cannot be simply extrapolated to C. parapsilosis Such species-specific characteristics may also influence their recognition and elimination by the host and the efficacy of antifungal drugs. Due to the availability of high-throughput, state-of-the-art experimental tools and molecular genetic methods adapted to C. parapsilosis, genome and transcriptome studies are now available that greatly contribute to our understanding of what makes this species a threat. In this review, we summarize 10 years of findings on C. parapsilosis pathogenesis, including the species' genetic properties, transcriptome studies, host responses, and molecular mechanisms of virulence. Antifungal susceptibility studies and clinician perspectives are discussed. We also present regional incidence reports in order to provide an updated worldwide epidemiology summary.

Hybridization and emergence of virulence in opportunistic human yeast pathogens

Hybridization between different species can result in the emergence of new lineages and adaptive phenotypes. Occasionally, hybridization in fungal organisms can drive the appearance of opportunistic lifestyles or shifts to new hosts, resulting in the emergence of novel pathogens. In recent years, an increasing number of studies have documented the existence of hybrids in diverse yeast clades, including some comprising human pathogens. Comparative and population genomics studies performed on these clades are enabling us to understand what roles hybridization may play in the evolution and emergence of a virulence potential towards humans. Here we survey recent genomic studies on several yeast pathogenic clades where hybrids have been identified, and discuss the broader implications of hybridization in the evolution and emergence of pathogenic lineages. © 2017 The Authors. Yeast published by John Wiley & Sons, Ltd.

Eukaryotic transporters for hydroxyderivatives of benzoic acid

Several yeast species catabolize hydroxyderivatives of benzoic acid. However, the nature of carriers responsible for transport of these compounds across the plasma membrane is currently unknown. In this study, we analyzed a family of genes coding for permeases belonging to the major facilitator superfamily (MFS) in the pathogenic yeast Candida parapsilosis. Our results revealed that these transporters are functionally equivalent to bacterial aromatic acid: H⁺ symporters (AAHS) such as GenK, MhbT and PcaK. We demonstrate that the genes HBT1 and HBT2 encoding putative transporters are highly upregulated in C. parapsilosis cells assimilating hydroxybenzoate substrates and the corresponding proteins reside in the plasma membrane. Phenotypic analyses of knockout mutants and hydroxybenzoate uptake assays provide compelling evidence that the permeases Hbt1 and Hbt2 transport the substrates that are metabolized via the gentisate (3-hydroxybenzoate, gentisate) and 3-oxoadipate pathway (4-hydroxybenzoate, 2,4-dihydroxybenzoate and protocatechuate), respectively. Our data support the hypothesis that the carriers belong to the AAHS family of MFS transporters. Phylogenetic analyses revealed that the orthologs of Hbt permeases are widespread in the subphylum Pezizomycotina, but have a sparse distribution among Saccharomycotina lineages. Moreover, these analyses shed additional light on the evolution of biochemical pathways involved in the catabolic degradation of hydroxyaromatic compounds.

MTL genotypes, phenotypic switching, and susceptibility profiles of Candida parapsilosis species group compared to Lodderomyces elongisporus

Reference isolates of Candida parapsilosis (n = 8), Candida metapsilosis (n = 6), Candida orthopsilosis (n = 7), and Lodderomyces elongisporus (n = 11) were analyzed to gain insight into their pathobiology and virulence mechanisms. Initial evaluation using BBL Chromagar Candida medium misidentified L. elongisporus isolates as C. albicans. Polymerase chain reaction analysis of isolate MTL idiomorphs revealed that all C. parapsilosis isolates were MTLa homozygous and no MTL α1, α2, a1, or a2 gene was detected in L. elongisporus isolates. For C. orthopsilosis, two isolates were MTLa homozygous and five were MTL-heterozygous. Similarly, one C. metapsilosis isolate was MTLα homozygous whereas five were MTL-heterozygous. Isolate phenotypic switching analysis revealed potential phenotypic switching in the MTLα homozygous C. metapsilosis isolate, resulting in concomitant elongated cell formation. Minimum inhibitory concentrations of fluconazole (FLC) and FK506, alone or in combination, were determined by checkerboard assay, with data analyzed using the fractional inhibitory concentration index model. Synergistic or additive effects of these compounds were commonly observed in C. parapsilosis and L. elongisporus isolates. No killer activity was observed in the studied isolates, as determined phenotypically. No significant difference in virulence was seen for the four species in a Galleria mellonella model (P > 0.05). In conclusion, our results demonstrated phenotypic switching of C. metapsilosis CBS 2315 and that FLC and FK506 represent a promising drug combination against C. parapsilosis and L. elongisporus. The findings of the present study contribute to our understanding of the biology, diagnosis, and new possible treatments of the C. parapsilosis species group and L. elongisporus.

Genome Diversity and Evolution in the Budding Yeasts (Saccharomycotina)

Considerable progress in our understanding of yeast genomes and their evolution has been made over the last decade with the sequencing, analysis, and comparisons of numerous species, strains, or isolates of diverse origins. The role played by yeasts in natural environments as well as in artificial manufactures, combined with the importance of some species as model experimental systems sustained this effort. At the same time, their enormous evolutionary diversity (there are yeast species in every subphylum of Dikarya) sparked curiosity but necessitated further efforts to obtain appropriate reference genomes. Today, yeast genomes have been very informative about basic mechanisms of evolution, speciation, hybridization, domestication, as well as about the molecular machineries underlying them. They are also irreplaceable to investigate in detail the complex relationship between genotypes and phenotypes with both theoretical and practical implications. This review examines these questions at two distinct levels offered by the broad evolutionary range of yeasts: inside the best-studied Saccharomyces species complex, and across the entire and diversified subphylum of Saccharomycotina. While obviously revealing evolutionary histories at different scales, data converge to a remarkably coherent picture in which one can estimate the relative importance of intrinsic genome dynamics, including gene birth and loss, vs. horizontal genetic accidents in the making of populations. The facility with which novel yeast genomes can now be studied, combined with the already numerous available reference genomes, offer privileged perspectives to further examine these fundamental biological questions using yeasts both as eukaryotic models and as fungi of practical importance.

Multiple Origins of the Pathogenic Yeast Candida orthopsilosis by Separate Hybridizations between Two Parental Species

Mating between different species produces hybrids that are usually asexual and stuck as diploids, but can also lead to the formation of new species. Here, we report the genome sequences of 27 isolates of the pathogenic yeast Candida orthopsilosis. We find that most isolates are diploid hybrids, products of mating between two unknown parental species (A and B) that are 5% divergent in sequence. Isolates vary greatly in the extent of homogenization between A and B, making their genomes a mosaic of highly heterozygous regions interspersed with homozygous regions. Separate phylogenetic analyses of SNPs in the A- and B-derived portions of the genome produces almost identical trees of the isolates with four major clades. However, the presence of two mutually exclusive genotype combinations at the mating type locus, and recombinant mitochondrial genomes diagnostic of inter-clade mating, shows that the species C. orthopsilosis does not have a single evolutionary origin but was created at least four times by separate interspecies hybridizations between parents A and B. Older hybrids have lost more heterozygosity. We also identify two isolates with homozygous genomes derived exclusively from parent A, which are pure non-hybrid strains. The parallel emergence of the same hybrid species from multiple independent hybridization events is common in plant evolution, but is much less documented in pathogenic fungi.

The genus Candida is one of the leading causes of fungal morbidity in humans. Many pathogenic Candida species are diploid, and do not have have a full sexual cycle. The evolutionary origin of Candida orthopsilosis is unclear. Here, we use whole genome sequencing of 27 C. orthopsilosis isolates from around the world to show that C. orthopsilosis arose from hybridization (or mating) of two distinct parental species. Unusually, the hybridization event did not occur only once; we identify at least four events, and we suggest that hybridization is ongoing. The “species” C. orthopsilosis therefore does not have one single origin. We have identified one of the parental lineages involved, but the other remains elusive. Our results suggest that inter-species hybridization has an evolutionary advantage. However, unlike in plant pathogens, it does not appear to result in increased virulence of C. orthopsilosis.

Evolution and Application of Inteins in Candida species: A Review

Inteins are invasive intervening sequences that perform an autocatalytic splicing from their host proteins. Among eukaryotes, these elements are present in many fungal species, including those considered opportunistic or primary pathogens, such as Candida spp. Here we reviewed and updated the list of Candida species containing inteins in the genes VMA, THRRS and GLT1 and pointed out the importance of these elements as molecular markers for molecular epidemiological researches and species-specific diagnosis, since the presence, as well as the size of these inteins, is polymorphic among the different species. Although absent in Candida albicans, these elements are present in different sizes, in some environmental Candida spp. and also in most of the non-albicans Candida spp. considered emergent opportunistic pathogens. Besides, the possible role of these inteins in yeast physiology was also discussed in the light of the recent findings on the importance of these elements as post-translational modulators of gene expression, reinforcing their relevance as alternative therapeutic targets for the treatment of non-albicans Candida infections, because, once the splicing of an intein is inhibited, its host protein, which is usually a housekeeping protein, becomes non-functional.

Identification of Non-Coding RNAs in the Candida parapsilosis Species Group

The Candida CTG clade is a monophyletic group of fungal species that translates CTG as serine, and includes the pathogens Candida albicans and Candida parapsilosis. Research has typically focused on identifying protein-coding genes in these species. Here, we use bioinformatic and experimental approaches to annotate known classes of non-coding RNAs in three CTG-clade species, Candida parapsilosis, Candida orthopsilosis and Lodderomyces elongisporus. We also update the annotation of ncRNAs in the C. albicans genome. The majority of ncRNAs identified were snoRNAs. Approximately 50% of snoRNAs (including most of the C/D box class) are encoded in introns. Most are within mono- and polycistronic transcripts with no protein coding potential. Five polycistronic clusters of snoRNAs are highly conserved in fungi. In polycistronic regions, splicing occurs via the classical pathway, as well as by nested and recursive splicing. We identified spliceosomal small nuclear RNAs, the telomerase RNA component, signal recognition particle, RNase P RNA component and the related RNase MRP RNA component in all three genomes. Stem loop IV of the U2 spliceosomal RNA and the associated binding proteins were lost from the ancestor of C. parapsilosis and C. orthopsilosis, following the divergence from L. elongisporus. The RNA component of the MRP is longer in C. parapsilosis, C. orthopsilosis and L. elongisporus than in S. cerevisiae, but is substantially shorter than in C. albicans.

Evolutionary genomics of yeast pathogens in the Saccharomycotina

Saccharomycotina comprises a diverse group of yeasts that includes numerous species of industrial or clinical relevance. Opportunistic pathogens within this clade are often assigned to the genus Candida but belong to phylogenetically distant lineages that also comprise non-pathogenic species. This indicates that the ability to infect humans has evolved independently several times among Saccharomycotina. Although the mechanisms of infection of the main groups of Candida pathogens are starting to be unveiled, we still lack sufficient understanding of the evolutionary paths that led to a virulent phenotype in each of the pathogenic lineages. Deciphering what genomic changes underlie the evolutionary emergence of a virulence trait will not only aid the discovery of novel virulence mechanisms but it will also provide valuable information to understand how new pathogens emerge, and what clades may pose a future danger. Here we review recent comparative genomics efforts that have revealed possible evolutionary paths to pathogenesis in different lineages, focusing on the main three agents of candidiasis worldwide: Candida albicans, C. parapsilosis and C. glabrata We will discuss what genomic traits may facilitate the emergence of virulence, and focus on two different genome evolution mechanisms able to generate drastic phenotypic changes and which have been associated to the emergence of virulence: gene family expansion and interspecies hybridization.

Genome comparison of Candida orthopsilosis clinical strains reveals the existence of hybrids between two distinct subspecies

The Candida parapsilosis species complex comprises a group of emerging human pathogens of varying virulence. This complex was recently subdivided into three different species: C. parapsilosis sensu stricto, C. metapsilosis, and C. orthopsilosis. Within the latter, at least two clearly distinct subspecies seem to be present among clinical isolates (Type 1 and Type 2). To gain insight into the genomic differences between these subspecies, we undertook the sequencing of a clinical isolate classified as Type 1 and compared it with the available sequence of a Type 2 clinical strain. Unexpectedly, the analysis of the newly sequenced strain revealed a highly heterozygous genome, which we show to be the consequence of a hybridization event between both identified subspecies. This implicitly suggests that C. orthopsilosis is able to mate, a so-far unanswered question. The resulting hybrid shows a chimeric genome that maintains a similar gene dosage from both parental lineages and displays ongoing loss of heterozygosity. Several of the differences found between the gene content in both strains relate to virulent-related families, with the hybrid strain presenting a higher copy number of genes coding for efflux pumps or secreted lipases. Remarkably, two clinical strains isolated from distant geographical locations (Texas and Singapore) are descendants of the same hybrid line, raising the intriguing possibility of a relationship between the hybridization event and the global spread of a virulent clone.

Survey and analysis of simple sequence repeats (SSRs) in three genomes of Candida species

Simple sequence repeats (SSRs) or microsatellites, which composed of tandem repeated short units of 1-6 bp, have been paying attention continuously. Here, the distribution, composition and polymorphism of microsatellites and compound microsatellites were analyzed in three available genomes of Candida species (Candida dubliniensis, Candida glabrata and Candida orthopsilosis). The results show that there were 118,047, 66,259 and 61,119 microsatellites in genomes of C. dubliniensis, C. glabrata and C. orthopsilosis, respectively. The SSRs covered more than 1/3 length of genomes in the three species. The microsatellites, which just consist of bases A and (or) T, such as (A)n, (T)n, (AT)n, (TA)n, (AAT)n, (TAA)n, (TTA)n, (ATA)n, (ATT)n and (TAT)n, were predominant in the three genomes. The length of microsatellites was focused on 6 bp and 9 bp either in the three genomes or in its coding sequences. What's more, the relative abundance (19.89/kbp) and relative density (167.87 bp/kbp) of SSRs in sequence of mitochondrion of C. glabrata were significantly great than that in any one of genomes or chromosomes of the three species. In addition, the distance between any two adjacent microsatellites was an important factor to influence the formation of compound microsatellites. The analysis may be helpful for further studying the roles of microsatellites in genomes' origination, organization and evolution of Candida species.

Genomics and the making of yeast biodiversity

Yeasts are unicellular fungi that do not form fruiting bodies. Although the yeast lifestyle has evolved multiple times, most known species belong to the subphylum Saccharomycotina (syn. Hemiascomycota, hereafter yeasts). This diverse group includes the premier eukaryotic model system, Saccharomyces cerevisiae; the common human commensal and opportunistic pathogen, Candida albicans; and over 1000 other known species (with more continuing to be discovered). Yeasts are found in every biome and continent and are more genetically diverse than angiosperms or chordates. Ease of culture, simple life cycles, and small genomes (∼10-20Mbp) have made yeasts exceptional models for molecular genetics, biotechnology, and evolutionary genomics. Here we discuss recent developments in understanding the genomic underpinnings of the making of yeast biodiversity, comparing and contrasting natural and human-associated evolutionary processes. Only a tiny fraction of yeast biodiversity and metabolic capabilities has been tapped by industry and science. Expanding the taxonomic breadth of deep genomic investigations will further illuminate how genome function evolves to encode their diverse metabolisms and ecologies.

Simple, Low-Cost Detection of Candida parapsilosis Complex Isolates and Molecular Fingerprinting of Candida orthopsilosis Strains in Kuwait by ITS Region Sequencing and Amplified Fragment Length Polymorphism Analysis

Candida parapsilosis has now emerged as the second or third most important cause of healthcare-associated Candida infections. Molecular studies have shown that phenotypically identified C. parapsilosis isolates represent a complex of three species, namely, C. parapsilosis, C. orthopsilosis and C. metapsilosis. Lodderomyces elongisporus is another species phenotypically closely related to the C. parapsilosis-complex. The aim of this study was to develop a simple, low cost multiplex (m) PCR assay for species-specific identification of C. parapsilosis complex isolates and to study genetic relatedness of C. orthopsilosis isolates in Kuwait. Species-specific amplicons from C. parapsilosis (171 bp), C. orthopsilosis (109 bp), C. metapsilosis (217 bp) and L. elongisporus (258 bp) were obtained in mPCR. Clinical isolates identified as C. parapsilosis (n = 380) by Vitek2 in Kuwait and an international collection of 27 C. parapsilosis complex and L. elongisporus isolates previously characterized by rDNA sequencing were analyzed to evaluate mPCR. Species-specific PCR and DNA sequencing of internal transcribed spacer (ITS) region of rDNA were performed to validate the results of mPCR. Fingerprinting of 19 clinical C. orthopsilosis isolates (including 4 isolates from a previous study) was performed by amplified fragment length polymorphism (AFLP) analysis. Phenotypically identified C. parapsilosis isolates (n = 380) were identified as C. parapsilosis sensu stricto (n = 361), C. orthopsilosis (n = 15), C. metapsilosis (n = 1) and L. elongisporus (n = 3) by mPCR. The mPCR also accurately detected all epidemiologically unrelated C. parapsilosis complex and L. elongisporus isolates. The 19 C. orthopsilosis isolates obtained from 16 patients were divided into 3 haplotypes based on ITS region sequence data. Seven distinct genotypes were identified among the 19 C. orthopsilosis isolates by AFLP including a dominant genotype (AFLP1) comprising 11 isolates recovered from 10 patients. A rapid, low-cost mPCR assay for detection and differentiation of C. parapsilosis, C. orthopsilosis, C. metapsilosis and L. elongisporus has been developed.

The Genomic Aftermath of Hybridization in the Opportunistic Pathogen Candida metapsilosis

Candida metapsilosis is a rarely-isolated, opportunistic pathogen that belongs to a clade of pathogenic yeasts known as the C. parapsilosis sensu lato species complex. To gain insight into the recent evolution of C. metapsilosis and the genetic basis of its virulence, we sequenced the genome of 11 clinical isolates from various locations, which we compared to each other and to the available genomes of the two remaining members of the complex: C. orthopsilosis and C. parapsilosis. Unexpectedly, we found compelling genomic evidence that C. metapsilosis is a highly heterozygous hybrid species, with all sequenced clinical strains resulting from the same past hybridization event involving two parental lineages that were approximately 4.5% divergent in sequence. This result indicates that the parental species are non-pathogenic, but that hybridization between them formed a new opportunistic pathogen, C. metapsilosis, that has achieved a worldwide distribution. We show that these hybrids are diploid and we identified strains carrying loci for both alternative mating types, which supports mating as the initial mechanism for hybrid formation. We trace the aftermath of this hybridization at the genomic level, and reconstruct the evolutionary relationships among the different strains. Recombination and introgression -resulting in loss of heterozygosis- between the two subgenomes have been rampant, and includes the partial overwriting of the MTLa mating locus in all strains. Collectively, our results shed light on the recent genomic evolution within the C. parapsilosis sensu lato complex, and argue for a re-definition of species within this clade, with at least five distinct homozygous lineages, some of which having the ability to form hybrids.

A case of Candida orthopsilosis associated septic arthritis in a patient with Systemic Lupus Erythematosus (SLE)

We report a case of persistent Candida orthopsilosis associated septic arthritis. Repeated isolation of C. orthopsilosis from tissue and joint fluid was confirmed by identification of the ITS region of the rRNA gene using a Candida-Specific Luminex based assay and gene sequencing of the D1/D2 regions. This was the first case of C. orthopsilosis associated septic arthritis reported in Jamaica and in the literature.

The Candida pathogenic species complex

Candida species are the most common causes of fungal infection. Approximately 90% of infections are caused by five species: Candida albicans, Candida glabrata, Candida tropicalis, Candida parapsilosis, and Candida krusei. Three (C. albicans, C. tropicalis, and C. parapsilosis) belong to the CTG clade, in which the CTG codon is translated as serine and not leucine. C. albicans remains the most commonly isolated but is decreasing relative to the other species. The increasing incidence of C. glabrata is related to its reduced susceptibility to azole drugs. Genome analysis suggests that virulence in the CTG clade is associated with expansion of gene families, particularly of cell wall genes. Similar independent processes took place in the C. glabrata species group. Gene loss and expansion in an ancestor of C. glabrata may have resulted in preadaptations that enabled pathogenicity.

Unexpected genomic variability in clinical and environmental strains of the pathogenic yeast Candida parapsilosis

Invasive candidiasis is the most commonly reported invasive fungal infection worldwide. Although Candida albicans remains the main cause, the incidence of emerging Candida species, such as C. parapsilosis is increasing. It has been postulated that C. parapsilosis clinical isolates result from a recent global expansion of a virulent clone. However, the availability of a single genome for this species has so far prevented testing this hypothesis at genomic scales. We present here the sequence of three additional strains from clinical and environmental samples. Our analyses reveal unexpected patterns of genomic variation, shared among distant strains, that argue against the clonal expansion hypothesis. All strains carry independent expansions involving an arsenite transporter homolog, pointing to the existence of directional selection in the environment, and independent origins of the two clinical isolates. Furthermore, we report the first evidence for the existence of recombination in this species. Altogether, our results shed new light onto the dynamics of genome evolution in C. parapsilosis.

Ribosomic DNA intergenic spacer 1 region is useful when identifying Candida parapsilosis spp. complex based on high-resolution melting analysis

The epidemiology of Candida parapsilosis and the closely related species C. orthopsilosis and C. metapsilosis has changed in recent years, justify the need to identify this complex at the species level. In this study we investigate the intergenic spacer 1 (IGS1) of the ribosomal DNA (rDNA) to evaluate the utility of this gene region as a phylogenetic molecular marker and the suitability of a high-resolution melting (HRM) strategy based on this region for identification of members of the C. parapsilosis spp. complex. We sequenced the IGS1 and the internal transcribed spacer (ITS) regions of the rDNA from 33 C. parapsilosis sensu lato strains. Although both regions are useful in identifying species, comparative sequence analysis showed that the diversity in the IGS1 region was higher than in the ITS sequences. We also developed an HRM analysis that reliably identifies C. parapsilosis spp. complex based on the amplification of 70 bp in the IGS1 region. All isolates were correctly identified with a confidence interval >98%. Our results demonstrate that HRM analysis based on the IGS1 region is a powerful tool for distinguishing C. parapsilosis from cryptic species.

Analysis of inteins in the Candida parapsilosis complex for simple and accurate species identification

Inteins are coding sequences that are transcribed and translated with flanking sequences and then are excised by an autocatalytic process. There are two types of inteins in fungi, mini-inteins and full-length inteins, both of which present a splicing domain containing well-conserved amino acid sequences. Full-length inteins also present a homing endonuclease domain that makes the intein a mobile genetic element. These parasitic genetic elements are located in highly conserved genes and may allow for the differentiation of closely related species of the Candida parapsilosis (psilosis) complex. The correct identification of the three psilosis complex species C. parapsilosis, Candida metapsilosis, and Candida orthopsilosis is very important in the clinical setting for improving antifungal therapy and patient care. In this work, we analyzed inteins that are present in the vacuolar ATPase gene VMA and in the threonyl-tRNA synthetase gene ThrRS in 85 strains of the Candida psilosis complex (46 C. parapsilosis, 17 C. metapsilosis, and 22 C. orthopsilosis). Here, we describe an accessible and accurate technique based on a single PCR that is able to differentiate the psilosis complex based on the VMA intein. Although the ThrRS intein does not distinguish the three species of the psilosis complex by PCR product size, it can differentiate them by sequencing and phylogenetic analysis. Furthermore, this intein is unusually present as both mini- and full-length forms in C. orthopsilosis. Additional population studies should be performed to address whether this represents a common intraspecific variability or the presence of subspecies within C. orthopsilosis.

Comparative genome analysis and gene finding in Candida species using CGOB

The Candida Gene Order Browser (CGOB) was developed as a tool to visualize and analyze synteny relationships in multiple Candida species, and to provide an accurate, manually curated set of orthologous Candida genes for evolutionary analyses. Here, we describe major improvements to CGOB. The underlying structure of the database has been changed significantly. Genomic features are now based directly on genome annotations rather than on protein sequences, which allows non-protein features such as centromere locations in Candida albicans and tRNA genes in all species to be included. The data set has been expanded to 13 species, including genomes of pathogens (C. albicans, C. parapsilosis, C. tropicalis, and C. orthopsilosis), and those of xylose-degrading species with important biotechnological applications (C. tenuis, Scheffersomyces stipitis, and Spathaspora passalidarum). Updated annotations of C. parapsilosis, C. dubliniensis, and Debaryomyces hansenii have been incorporated. We discovered more than 1,500 previously unannotated genes among the 13 genomes, ranging in size from 29 to 3,850 amino acids. Poorly conserved and rapidly evolving genes were also identified. Re-analysis of the mating type loci of the xylose degraders suggests that C. tenuis is heterothallic, whereas both Spa. passalidarum and S. stipitis are homothallic. As well as hosting the browser, the CGOB website (http://cgob.ucd.ie) gives direct access to all the underlying genome annotations, sequences, and curated orthology data.

Candida parapsilosis is a significant neonatal pathogen: a systematic review and meta-analysis

BACKGROUND

Candida is the third most common cause of late-onset neonatal sepsis in infants born at <1500 g. Candida parapsilosis infections are increasingly reported in preterm neonates in association with indwelling catheters.

METHODS

We systematically reviewed neonatal literature and synthesized data pertaining to percentage of C. parapsilosis infections and mortality by meta-analyses. We also reviewed risk factors, virulence determinants, antimicrobial susceptibility patterns and outlined clinical management strategies.

RESULTS

C. parapsilosis infections comprised 33.47% (95% confidence interval [CI]: 30.02, 37.31) of all neonatal Candida infections. C. parapsilosis rates were similar in studies performed before the year 2000, 33.53% (95% CI: 30.06, 37.40) (28 studies), to those after 2000, 27.00% (95% CI: 8.25, 88.37) (8 studies). The mortality due to neonatal C. parapsilosis infections was 10.02% (95% CI: 7.66, 13.12). Geographical variations in C. parapsilosis infections included a low incidence in Europe and higher incidence in North America and Australia. Biofilm formation was a significant virulence determinant and predominant risk factors for C. parapsilosis infections were prematurity, prior colonization and catheterization. Amphotericin B remains the antifungal drug of choice and combination therapy with caspofungin or other echinocandins may be considered in resistant cases.

CONCLUSION

C. parapsilosis is a significant neonatal pathogen, comprises a third of all Candida infections and is associated with 10% mortality. Availability of tools for genetic manipulation of this organism will identify virulence determinants and organism characteristics that may explain predilection for preterm neonates. Strategies to prevent horizontal transmission in the neonatal unit are paramount in decreasing infection rates.

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.

A pipeline for automated annotation of yeast genome sequences by a conserved-synteny approach

BACKGROUND

Yeasts are a model system for exploring eukaryotic genome evolution. Next-generation sequencing technologies are poised to vastly increase the number of yeast genome sequences, both from resequencing projects (population studies) and from de novo sequencing projects (new species). However, the annotation of genomes presents a major bottleneck for de novo projects, because it still relies on a process that is largely manual.

RESULTS

Here we present the Yeast Genome Annotation Pipeline (YGAP), an automated system designed specifically for new yeast genome sequences lacking transcriptome data. YGAP does automatic de novo annotation, exploiting homology and synteny information from other yeast species stored in the Yeast Gene Order Browser (YGOB) database. The basic premises underlying YGAP's approach are that data from other species already tells us what genes we should expect to find in any particular genomic region and that we should also expect that orthologous genes are likely to have similar intron/exon structures. Additionally, it is able to detect probable frameshift sequencing errors and can propose corrections for them. YGAP searches intelligently for introns, and detects tRNA genes and Ty-like elements.

CONCLUSIONS

In tests on Saccharomyces cerevisiae and on the genomes of Naumovozyma castellii and Tetrapisispora blattae newly sequenced with Roche-454 technology, YGAP outperformed another popular annotation program (AUGUSTUS). For S. cerevisiae and N. castellii, 91-93% of YGAP's predicted gene structures were identical to those in previous manually curated gene sets. YGAP has been implemented as a webserver with a user-friendly interface at http://wolfe.gen.tcd.ie/annotation.