Isolation of Saccharomycopsis species from plant material

Saccharomycopsis species are natural organic sulphur auxotrophs. Their genomes do not encode genes for the uptake and assimilation of sulphate and thus these species cannot grow on media lacking e.g. methionine. Due to the similarity between sulphate and selenate, uptake and assimilation of selenate occurs through the same pathway starting from sulphate transporters encoded by the homologs of the SUL1 and SUL2 genes in S. cerevisiae. Lack of these transporters renders Saccharomycopsis species resistant to selenate levels that are toxic to other microorganisms. We used this feature to enrich environmental samples for Saccharomycopsis species. This led to the isolation of S. schoenii, S. lassenensis and a hitherto undescribed Saccharomycopsis species with limited by-catch of other yeasts, mainly belonging to Metschnikowia and Hanseniaspora. We performed growth and predation assays to characterize the potential of these new isolates as predacious yeasts. Most Saccharomycopsis species are temperature sensitive and cannot grow at 37°C; with the exception of S. lassenensis strains. Predation assays with S. schoenii and S. cerevisiae as prey indicated that predation was enhanced at 20°C compared to 30°C. We crossed an American isolate of S. schoenii with our German isolate using marker directed breeding. Viable progeny indicated that both strains are interfertile and belong to the same biological species. S. lassenensis is heterothallic, while S. schoenii and the new Saccharomycopsis isolate, for which we suggest the name S. geisenheimensis sp. nov., are homothallic.

Mosaic Genome of a British Cider Yeast

Hybrid formation and introgressions had a profound impact on fermentative yeasts domesticated for beer, wine and cider fermentations. Here we provide a comparative genomic analysis of a British cider yeast isolate (E1) and characterize its fermentation properties. E1 has a Saccharomyces uvarum genome into which ~102 kb of S. eubayanus DNA were introgressed that replaced the endogenous homologous 55 genes of chromosome XIV between YNL182C and YNL239W. Sequence analyses indicated that the DNA donor was either a lager yeast or a yet unidentified S. eubayanus ancestor. Interestingly, a second introgression event added ~66 kb of DNA from Torulaspora microellipsoides to the left telomere of SuCHRX. This region bears high similarity with the previously described region C introgression in the wine yeast EC1118. Within this region FOT1 and FOT2 encode two oligopeptide transporters that promote improved nitrogen uptake from grape must in E1, as was reported for EC1118. Comparative laboratory scale grape must fermentations between the E1 and EC1118 indicated beneficial traits of faster consumption of total sugars and higher glycerol production but low acetic acid and reduced ethanol content. Importantly, the cider yeast strain produced high levels of fruity ester, including phenylethyl and isoamyl acetate.

Improved gene-targeting efficiency upon starvation in Saccharomycopsis

Commonly used fungal transformation protocols rely on the use of either electroporation or the lithium acetate/single strand carrier DNA/Polyethylene glycol/heat shock method. We have used the latter method previously in establishing DNA-mediated transformation in Saccharomycopsis schoenii, a CTG-clade yeast that exhibits necrotrophic mycoparasitism. To elucidate the molecular mechanisms of predation by Saccharomycopsis we aim at gene-function analyses to identify virulence-related pathways and genes. However, in spite of a satisfactory transformation efficiency our efforts were crippled by high frequency of ectopic integration of disruption cassettes. Here, we show that overnight starvation of S. schoenii cells, while reducing the number of transformants, resulted in a substantial increase in gene-targeting via homologous recombination. To demonstrate this, we have deleted the S. schoenii CHS1, HIS3 and LEU2 genes and determined the required size of the flanking homology regions. Additionally, we complemented the S. schoenii leu2 mutant with heterologous LEU2 gene from Saccharomycopsis fermentans. To demonstrate the usefulness of our approach we also generated a S. fermentans leu2 strain, suggesting that this approach may have broader applicability.

The genome sequence of the Champagne Epernay Geisenheim wine yeast reveals its hybrid nature

Lager yeasts are hybrids between Saccharomyces cerevisiae and S. eubayanus. Wine yeast biodiversity, however, has only recently been discovered to include besides pure S. cerevisiae strains also hybrids between different Saccharomyces yeasts as well as introgressions from non-Saccharomyces species. Here, we analysed the genome of the Champagne Epernay Geisenheim (CEG) wine yeast. This yeast is an allotetraploid (4n - 1) hybrid of S. cerevisiae harbouring a substantially reduced S. kudriavzevii genome contributing only 1/3 of a full genome equivalent. We identified a novel oligopeptide transporter gene, FOT4, in CEG located on chromosome XVI. FOT genes were originally derived from Torulaspora microellipsoides and FOT4 arose by non-allelic recombination between adjacent FOT1 and FOT2 genes. Fermentations of CEG in Riesling and Müller-Thurgau musts were compared with the S. cerevisiae Geisenheim wine yeast GHM, which does not carry FOT genes. At low temperature (10°C), CEG completed fermentations faster and produced increased levels of higher alcohols (e.g. isoamyl alcohol). At higher temperature (18°C), CEG produced higher amounts of the pineapple-like alkyl esters i-butyric and propionic acid ethyl esters compared to GHM. The hybrid nature of CEG thus provides advantages in grape must fermentations over S. cerevisiae wine yeasts, especially with regard to aroma production.

PCR-based gene targeting in Hanseniaspora uvarum

Lack of gene-function analyses tools limits studying the biology of Hanseniaspora uvarum, one of the most abundant yeasts on grapes and in must. We investigated a rapid PCR-based gene targeting approach for one-step gene replacement in this diploid yeast. To this end, we generated and validated two synthetic antibiotic resistance genes, pFA-hygXL and pFA-clnXL, providing resistance against hygromycin and nourseothricin, respectively, for use with H. uvarum. Addition of short flanking-homology regions of 56-80 bp to these selection markers via PCR was sufficient to promote gene targeting. We report here the deletion of the H. uvarum LEU2 and LYS2 genes with these marker genes via two rounds of consecutive transformations, each resulting in the generation of auxotrophic strains (leu2/leu2; lys2/lys2). The hereby constructed leucine auxotrophic leu2/leu2 strain was subsequently complemented in a targeted manner, thereby further validating this approach. PCR-based gene targeting in H. uvarum was less efficient than in Saccharomyces cerevisiae. However, this approach, combined with the availability of two marker genes, provides essential tools for directed gene manipulations in H. uvarum.

Co-Fermentations of Kveik with Non-Conventional Yeasts for Targeted Aroma Modulation

Kveik are consortia of yeast used for farmhouse ale production in Western Norway. Yeast strains derived from these mixtures are known, for example, for their high fermentation rate, thermotolerance, lack of phenolic off flavor production (POF-) and strong flocculation phenotype. In this study, we used five single cell yeast isolates from different Kveik yeasts, analyzed their fermentation and flavor production, and compared it with a typical yeast used in distilleries using 20 °C and 28 °C as the fermentation temperatures. One of the isolates, Kveik No 3, showed an impairment of maltotriose utilization and thus a reduced ethanol yield. Kveik fermentations for spirit production often harbor bacteria for flavor enrichment. We sought to improve Kveik fermentations with non-conventional yeasts (NCY). To this end we co-fermented Kveik isolates with Hanseniaspora uvarum, Meyerozyma guilliermondii and Pichia kudriavzevii using 5:1 ratios (Kveik vs. NCY) at 20 °C. The combinations of Kveik No 1 with P. kudriavzevii and Kveik No 1 with Hanseniaspora uvarum showed substantially increased amounts of specific volatile aroma compounds that were previously identified in the NCYs. Our results indicate that Kveik isolates appear to be suitable for co-fermentations with certain NCY to enhance beer or spirit fermentations, increasing the potential of these yeasts for beverage productions.

Psychological Adjustment in the Context of Perinatal Cancer

Aims: To assess the influence of pregnancy and recent motherhood on the psychological adjustment to cancer in women diagnosed with a perinatal cancer. Procedure: ECHOCALG is an exploratory and comparative study combining quantitative and qualitative methods. Twenty-four women who had received a perinatal cancer diagnosis (75% had breast cancer, 25% had brain or colon cancer, Hodgkin or melanoma) completed the MAC44 scale and responded to a semi-structured clinical interview to identify the psychological adjustment to cancer. Eighteen of them responded to a semi-structured interview to identify the conditions of psychological adaptation to the disease, as well as the defense mechanisms used. The data were compared with that of a control group of nineteen women diagnosed with non-perinatal and non-metastatic breast cancer, aged less than 45.

Results: Women diagnosed with perinatal cancer showed more difficulty adjusting to the disease than control women. Denial and avoidance are strongly correlated with a negative adjustment to cancer. The interviews showed at the start of treatment the presence of defense mechanisms such as denial and trivialization as well as a suspension of the process of psychological adaptation to the disease and the treatments. The distress of a mother is linked to the feeling of being unable to take care of the baby and to cope concomitantly with motherhood and illness, as well as difficulties related to sexuality and emotional and social support.

Conclusion: Pregnancy and recent motherhood have an impact on the adjustment to cancer. Women with perinatal cancer show a negative adjustment and an important psychological distress linked to difficulties of mothering and physical and emotional consequences of treatment.

[Validation of the questionnaire for assessing the childbirth experience (QACE) in a French population]

BACKGROUND

A woman's negative perception of her subjective childbirth experience can have consequences on the mother's psychological state and on early mother-baby relationships. To date, there is no validated tool in France allowing to evaluate childbirth experience in a multidimensional way. The aim of this study is to validate the Questionnaire Assessing the Childbirth Experience (QEVA) in a French sample of mothers. This tool was developed in a previous study where the authors combined 25 items into 6 dimensions: representations and expectations, sensory perceptions, feeling of control, perceived social support (medical staff and partner), emotions (positive and negative) and first moments with the baby.

METHODS

The sample included 256 women recruited in a maternity ward. Sociodemographic and obstetric characteristics of our sample were compared to those of the French national perinatal survey. The structure of the QEVA with 17 items was explored by an exploratory structural equation modeling (ESEM). An analysis of the internal consistency was conducted on the sub-scores of the identified factors, and the concurrent validity was assessed with the Peri-traumatic Distress Inventory (PDI) through a correlation and its associated t-test.

RESULTS

The characteristics of our sample and those of the national perinatal survey do not differ on age, marital status, parity, cannabis use, infertility treatment, epidural and baby weight, in favour of the good representativeness of our sample. The study of the QEVA structure revealed a 4-dimensional structure. Analysis of the psychometric qualities showed a good internal consistency, with an observed alpha value ranging from 0.69 to 0.86. The QEVA also shows a good concurrent validity with the peri-traumatic distress scores (r=0.51).

CONCLUSION

To date, the QEVA is the first standardized tool allowing a multidimensional evaluation of the subjective experience of childbirth. It has been validated on a French population using an exploratory structural equation modeling. This tool, which is simple to use and well accepted by mothers, enables health professionals not only to screen mothers experiencing difficult childbirth and in need of support, but also to adapt health care according to the dimensions of the birth experience and its associated difficulties (emotions during the birth, interactions with health professionals, first moments with the baby, or post-partum emotions).

Effect of Isomixing on Grape Must Fermentations of ATF1-Overexpressing Wine Yeast Strains

Speeding up grape must fermentation would be of great economic benefit. We subjected Saccharomyces cerevisiae VIN13 and two recombinant VIN13-strains expressing ATF1 alleles under two different promoters (either PGK1 or HXT7) to four styles of grape must fermentations; we then assessed the effect of constantly stirring a must fermentation (isomixing). The four different fermentation setups were as follows: isomixed, closed in an ANKOM Rf Gas productions system; isomixed, open in a stirred tall tube cylinder; static, closed constituting a conventional fermentation in a wine bottle equipped with an airlock and static; and static, open in a tall tube cylinder (without stirring). We report on major fermentation parameters and the volatile aroma compositions generated in the finished wines. The primary fermentations of the strains subjected to constant stirring finished after 7 days, whereas the static fermentations reached dryness after 19 days. The wines derived from isomixed fermentations produced approximately 0.7% less ethanol compared to the unstirred fermentations. The speed that the isomixed fermentation took to reach completion may provide an alternative to static fermentations in the preparation of base wines for sparkling wine production. The observed increase of volatiles of isomixed fermentations merits further investigation.

Blending wine yeast phenotypes with the aid of CRISPR DNA editing technologies

In recent years, CRISPR/Cas9-based genetic editing has become a mainstay in many laboratories including manipulations done with yeast. We utilized this technique to generate a self-cloned wine yeast strain that overexpresses two genes of oenological relevance i.e. the glycerol-3-phosphate dehydrogenase 1 (GPD1) and the alcohol acetyltransferase 1 (ATF1) directly implicated in glycerol and acetate ester production respectively. Riesling wine made from the resulting strain showed increased glycerol and acetate ester levels compared to the parental strain. In addition, significantly less acetic acid levels were measured in wine made with yeast containing both genetic alterations compared to wine made with the strain that only overexpresses GPD1. Thus, this strain provides an alternative strategy for alleviating the accumulation of acetic acid once glycerol production is favoured during alcoholic fermentation with the addition of dramatically increasing acetate esters production.

The Whiff of Wine Yeast Innovation: Strategies for Enhancing Aroma Production by Yeast during Wine Fermentation

Despite being used chiefly for fermenting the sugars of grape must to alcohol, wine yeasts (most prominently Saccharomyces cerevisiae) play a pivotal role in the final aroma profiles of wines. Strain selection, intentionally incorporating non-Saccharomyces yeast in so-called mixed-culture fermentations, and genetic modifications of S. cerevisiae have all been shown to greatly enhance the chemical composition and sensory profile of wines. In this Review, we highlight how wine researchers employ fermenting yeasts to expand on the aroma profiles of the wines they study.

A script for initiating molecular biology studies with non-conventional yeasts based on Saccharomycopsis schoenii

Non-conventional yeasts (NCYs), i.e. all yeasts other than Saccharomyces cerevisiae, are emerging as novel production strains and gain more and more attention to exploit their unique properties. Yet, these yeasts can hardly compete against the advanced methodology and genetic tool kit available for exploiting and engineering S. cerevisiae. Currently, for many NCYs one has to start from scratch to initiate molecular genetic manipulations, which is often time consuming and not straight-forward. More so because utilization of S. cerevisiae tools based on short-flank mediated homologous recombination or plasmid biology are not readily applicable in NCYs. Here we present a script with discrete steps that will lead to the development of a basic and expandable molecular toolkit for ascomycetous NCYs and will allow genetic engineering of novel platform strains. For toolkit development the highly efficient in vivo recombination efficiency of S. cerevisiae is utilized in the generation and initial testing of tools. The basic toolkit includes promoters, reporter genes, selectable markers based on dominant antibiotic resistance genes and the generation of long-flanking homology disruption cassettes. The advantage of having pretested molecular tools that function in a heterologous host facilitate NCY strain manipulations. We demonstrate the usefulness of this script on Saccharomycopsis schoenii, a predator yeast with useful properties in fermentation and fungal biocontrol.

Multi-omics characterization of the necrotrophic mycoparasite Saccharomycopsis schoenii

Pathogenic yeasts and fungi are an increasing global healthcare burden, but discovery of novel antifungal agents is slow. The mycoparasitic yeast Saccharomycopsis schoenii was recently demonstrated to be able to kill the emerging multi-drug resistant yeast pathogen Candida auris. However, the molecular mechanisms involved in the predatory activity of S. schoenii have not been explored. To this end, we de novo sequenced, assembled and annotated a draft genome of S. schoenii. Using proteomics, we confirmed that Saccharomycopsis yeasts have reassigned the CTG codon and translate CTG into serine instead of leucine. Further, we confirmed an absence of all genes from the sulfate assimilation pathway in the genome of S. schoenii, and detected the expansion of several gene families, including aspartic proteases. Using Saccharomyces cerevisiae as a model prey cell, we honed in on the timing and nutritional conditions under which S. schoenii kills prey cells. We found that a general nutrition limitation, not a specific methionine deficiency, triggered predatory activity. Nevertheless, by means of genome-wide transcriptome analysis we observed dramatic responses to methionine deprivation, which were alleviated when S. cerevisiae was available as prey, and therefore postulate that S. schoenii acquired methionine from its prey cells. During predation, both proteomic and transcriptomic analyses revealed that S. schoenii highly upregulated and translated aspartic protease genes, probably used to break down prey cell walls. With these fundamental insights into the predatory behavior of S. schoenii, we open up for further exploitation of this yeast as a biocontrol yeast and/or source for novel antifungal agents.

Expansion of a Telomeric FLO/ALS-Like Sequence Gene Family in Saccharomycopsis fermentans

Non-Saccharomyces species have been recognized for their beneficial contribution to fermented food and beverages based on their volatile compound formation and their ability to ferment glucose into ethanol. At the end of fermentation brewer's yeast flocculate which provides an easy means of separation of yeasts from green beer. Flocculation in Saccharomyces cerevisiae requires a set of flocculation genes. These FLO-genes, FLO1, FLO5, FLO9, FLO10, and FLO11, are located at telomeres and transcription of these adhesins is regulated by Flo8 and Mss11. Here, we show that Saccharomycopsis fermentans, an ascomycete yeast distantly related to S. cerevisiae, possesses a very large FLO/ALS-like Sequence (FAS) family encompassing 34 genes. Fas proteins are variable in size and divergent in sequence and show similarity to the Flo1/5/9 family. Fas proteins show the general build with a signal peptide, an N-terminal carbohydrate binding PA14 domain, a central region differing by the number of repeats and a C-terminus with a consensus sequence for GPI-anchor attachment. Like FLO genes in S. cerevisiae, FAS genes are mostly telomeric with several paralogs at each telomere. We term such genes that share evolutionary conserved telomere localization "telologs" and provide several other examples. Adhesin expression in S. cerevisiae and filamentation in Candida albicans is regulated by Flo8 and Mss11. In Saccharomycopsis we identified only a single protein with similarity to Flo8 based on sequence similarity and the presence of a LisH domain.

The mycoparasitic yeast Saccharomycopsis schoenii predates and kills multi-drug resistant Candida auris

Candida auris has recently emerged as a multi-drug resistant fungal pathogen that poses a serious global health threat, especially for patients in hospital intensive care units (ICUs). C. auris can colonize human skin and can spread by physical contact or contaminated surfaces and equipment. Here, we show that the mycoparasitic yeast Saccharomycopsis schoenii efficiently kills both sensitive and multi-drug resistant isolates of C. auris belonging to the same clade, as well as clinical isolates of other pathogenic species of the Candida genus suggesting novel approaches for biocontrol.

The APSES protein Sok2 is a positive regulator of sporulation in Ashbya gossypii

Ashbya gossypii is a homothallic, flavinogenic, filamentous ascomycete that starts overproduction of riboflavin and fragments its mycelium quantitatively into spore producing sporangia at the end of a growth phase. Mating is not required for sporulation and the standard homothallic laboratory strain is a MATa strain. Here we show that ectopic expression of Saccharomyces cerevisiae MATα2 in A. gossypii completely suppresses sporulation, inhibits riboflavin overproduction and downregulates among others AgSOK2. AgSok2 belongs to a fungal-specific group of (APSES) transcription factors. Deletion of AgSOK2 strongly reduces riboflavin production and blocks sporulation. The initiator of meiosis, AgIME1, is a transcription factor essential for sporulation. We characterized the AgIME1 promoter region required for complementation of the Agime1 mutant. Reporter assays with AgIME1 promoter fragments fused to lacZ showed that AgSok2 does not control AgIME1 transcription. However, global transcriptome analysis identified two other essential regulators of sporulation, AgIME2 and AgNDT80, as potential targets of AgSok2. Our data suggest that sporulation and riboflavin production in A. gossypii are under mating type locus and nutritional control. Sok2, a target of the cAMP/protein kinase A pathway, serves as a central positive regulator to promote sporulation. This contrasts Saccharomyces cerevisiae where Sok2 is a repressor of IME1 transcription.

Differential stress response of Saccharomyces hybrids revealed by monitoring Hsp104 aggregation and disaggregation

Proteotoxic stress may occur upon exposure of yeast cells to different stress conditions. The induction of stress response mechanisms is important for cells to adapt to changes in the environment and ensure survival. For example, during exposure to elevated temperatures the expression of heat shock proteins such as Hsp104 is induced in yeast. Hsp104 extracts misfolded proteins from aggregates to promote their refolding. We used an Hsp104-GFP reporter to analyze the stress profiles of Saccharomyces species hybrids. To this end a haploid S. cerevisiae strain, harboring a chromosomal HSP104-GFP under control of its endogenous promoter, was mated with stable haploids of S. bayanus, S. cariocanus, S. kudriavzevii, S. mikatae, S. paradoxus and S. uvarum. Stress response behaviors in these hybrids were followed over time by monitoring the appearance and dissolution of Hsp104-GFP foci upon heat shock. General stress tolerance of these hybrids was related to the growth rate detected during exposure to e.g. ethanol and oxidizing agents. We observed that hybrids were generally more resistant to high temperature and ethanol stress compared to their parental strains. Amongst the hybrids differential responses regarding the appearance of Hsp104-foci and the time required for dissolving these aggregates were observed. The S. cerevisiae/S. paradoxus hybrid, combining the two most closely related strains, performed best under these conditions.

Acetaldehyde as an Intermediate in the Electroreduction of Carbon Monoxide to Ethanol on Oxide-Derived Copper

Oxide‐derived copper (OD‐Cu) electrodes exhibit unprecedented CO reduction performance towards liquid fuels, producing ethanol and acetate with >50 % Faradaic efficiency at −0.3 V (vs. RHE). By using static headspace‐gas chromatography for liquid phase analysis, we identify acetaldehyde as a minor product and key intermediate in the electroreduction of CO to ethanol on OD‐Cu electrodes. Acetaldehyde is produced with a Faradaic efficiency of ≈5 % at −0.33 V (vs. RHE). We show that acetaldehyde forms at low steady‐state concentrations, and that free acetaldehyde is difficult to detect in alkaline solutions using NMR spectroscopy, requiring alternative methods for detection and quantification. Our results represent an important step towards understanding the CO reduction mechanism on OD‐Cu electrodes.

Fungal model systems and the elucidation of pathogenicity determinants

Fungi have the capacity to cause devastating diseases of both plants and animals, causing significant harvest losses that threaten food security and human mycoses with high mortality rates. As a consequence, there is a critical need to promote development of new antifungal drugs, which requires a comprehensive molecular knowledge of fungal pathogenesis. In this review, we critically evaluate current knowledge of seven fungal organisms used as major research models for fungal pathogenesis. These include pathogens of both animals and plants; Ashbya gossypii, Aspergillus fumigatus, Candida albicans, Fusarium oxysporum, Magnaporthe oryzae, Ustilago maydis and Zymoseptoria tritici. We present key insights into the virulence mechanisms deployed by each species and a comparative overview of key insights obtained from genomic analysis. We then consider current trends and future challenges associated with the study of fungal pathogenicity.

Chromosome number reduction in Eremothecium coryli by two telomere-to-telomere fusions

The genus Eremothecium belongs to the Saccharomyces complex of pre-whole-genome duplication (WGD) yeasts and contains both dimorphic and filamentous species. We established the 9.1-Mb draft genome of Eremothecium coryli, which encodes 4,682 genes, 186 tRNA genes, and harbors several Ty3 transposons as well as more than 60 remnants of transposition events (LTRs). The initial de novo assembly resulted in 19 scaffolds, which were assembled based on synteny to other Eremothecium genomes into six chromosomes. Interestingly, we identified eight E. coryli loci that bear centromeres in the closely related species E. cymbalariae. Two of these E. coryli loci, CEN1 and CEN8, however, lack conserved DNA elements and did not convey centromere function in a plasmid stability assay. Correspondingly, using a comparative genomics approach we identified two telomere-to-telomere fusion events in E. coryli as the cause of chromosome number reduction from eight to six chromosomes. Finally, with the genome sequences of E. coryli, E. cymbalariae, and Ashbya gossypii a reconstruction of three complete chromosomes of an Eremothecium ancestor revealed that E. coryli is more syntenic to this ancestor than the other Eremothecium species.

An indirect assay for volatile compound production in yeast strains

Traditional flavor analysis relies on gas chromatography coupled to mass spectrometry (GC-MS) methods. Here we describe an indirect method coupling volatile compound formation to an ARO9-promoter-LacZ reporter gene. The resulting β-galactosidase activity correlated well with headspace solid phase micro extraction (HS/SPME) GC-MS data, particularly with respect to the formation of rose flavor. This tool enables large-scale screening of yeast strains and their progeny to identify the most flavor active strains.

Subcellular localization of the fatty acyl reductase involved in pheromone biosynthesis in the tobacco budworm, Heliothis virescens (Noctuidae: Lepidoptera)

Sex pheromone components are produced in specialized glands of female moths via well-characterized biosynthetic pathways, where a Fatty Acyl Reductase (FAR) is often essential for producing the specific ratio of the different pheromone components. The subcellular localization and membrane topology of FARs is important for understanding how pheromones are synthesized and exported to the exterior for release. We investigated the subcellular localization of HvFAR from the noctuid moth Heliothis virescens by producing recombinant fusion proteins with green fluorescent protein (GFP) in yeast. A C-terminally tagged construct was localized to the endoplasmic reticulum (ER) and retained full reductive activity on a broad range of saturated and unsaturated fatty acyl precursors. In contrast, an N-terminally-tagged construct was poorly expressed in the cytoplasm and was not enzymatically active, indicating that HvFAR requires a free N-terminal for both proper targeting and catalytic activity. A series of truncations of the N-and C-termini of HvFAR was conducted based on in silico-predicted hydrophobic domains and transmembrane regions. The N-terminally truncated protein was found in the cytoplasm and did not retain activity, emphasizing the importance of the N-terminal for FAR function. In addition, the orientation in the membrane of the C-terminus-tagged HvFAR-GFP construct was analyzed using a fluorescence protease protection (FPP) assay, implying that the C-terminal of HvFAR is orientated towards the cytoplasm. These results, together with previous data on the localization of desaturases, confirm the importance of the ER as a subcellular site of pheromone production.

Breeding of lager yeast with Saccharomyces cerevisiae improves stress resistance and fermentation performance

Lager beer brewing relies on strains collectively known as Saccharomyces carlsbergensis, which are hybrids between S. cerevisiae and S. eubayanus-like strains. Lager yeasts are particularly adapted to low-temperature fermentations. Selection of new yeast strains for improved traits or fermentation performance is laborious, due to the allotetraploid nature of lager yeasts. Initially, we have generated new F1 hybrids by classical genetics, using spore clones of lager yeast and S. cerevisiae and complementation of auxotrophies of the single strains upon mating. These hybrids were improved on several parameters, including growth at elevated temperature and resistance against high osmolarity or high ethanol concentrations. Due to the uncertainty of chromosomal make-up of lager yeast spore clones, we introduced molecular markers to analyse mating-type composition by PCR. Based on these results, new hybrids between a lager and an ale yeast strain were isolated by micromanipulation. These hybrids were not subject to genetic modification. We generated and verified 13 hybrid strains. All of these hybrid strains showed improved stress resistance as seen in the ale parent, including improved survival at the end of fermentation. Importantly, some of the strains showed improved fermentation rates using 18° Plato at 18-25°C. Uniparental mitochondrial DNA inheritance was observed mostly from the S. cerevisiae parent.

Yap1-dependent oxidative stress response provides a link to riboflavin production in Ashbya gossypii

Ashbya gossypii is a natural overproducer of riboflavin. Overproduction of riboflavin can be induced by environmental stress, e.g. nutritional or oxidative stress. The Yap-protein family has a well-documented role in stress response. Particularly, Yap1 has a major role in directing the oxidative stress responses. The A. gossypii YAP-family consists of only three genes in contrast to its closest relative Eremothecium cymbalariae, which has four YAP-homologs. Gene order at Eremothecium YAP-loci is conserved with the reconstructed yeast ancestor. AgYap1p is unique amongst Yap-homologs as it lacks the cysteine-rich domains (CRDs). AgYAP1 expression is inducible and GFP-AgYap1 localizes to the nucleus. Agyap1 mutants displayed higher sensitivity against oxidative stress - H(2)O(2) and menadione - and are strongly reduced in riboflavin production. High levels of cAMP, which also reduce riboflavin production, show a synergistic effect on this sensitivity. AgYAP1 and a chimera of AgYAP1 (with the DNA-binding domain) and ScYAP1 (with the CRDs) can both complement the Scyap1 oxidative stress sensitivity. This suggests that the DNA-binding sites of ScYap1 are conserved in A. gossypii. Expression of AgRIB4, which contains three putative Yap1-binding sites, assayed via a lacZ-reporter gene was strongly reduced in an Agyap1 mutant suggesting a direct involvement of AgYap1 in riboflavin production. Furthermore, our data show that application of H(2)O(2) stress leads to an increase in riboflavin production in a Yap1-dependent manner.

Genome evolution in the eremothecium clade of the Saccharomyces complex revealed by comparative genomics

We used comparative genomics to elucidate the genome evolution within the pre-whole-genome duplication genus Eremothecium. To this end, we sequenced and assembled the complete genome of Eremothecium cymbalariae, a filamentous ascomycete representing the Eremothecium type strain. Genome annotation indicated 4712 gene models and 143 tRNAs. We compared the E. cymbalariae genome with that of its relative, the riboflavin overproducer Ashbya (Eremothecium) gossypii, and the reconstructed yeast ancestor. Decisive changes in the Eremothecium lineage leading to the evolution of the A. gossypii genome include the reduction from eight to seven chromosomes, the downsizing of the genome by removal of 10% or 900 kb of DNA, mostly in intergenic regions, the loss of a TY3-Gypsy-type transposable element, the re-arrangement of mating-type loci, and a massive increase of its GC content. Key species-specific events are the loss of MNN1-family of mannosyltransferases required to add the terminal fourth and fifth α-1,3-linked mannose residue to O-linked glycans and genes of the Ehrlich pathway in E. cymbalariae and the loss of ZMM-family of meiosis-specific proteins and acquisition of riboflavin overproduction in A. gossypii. This reveals that within the Saccharomyces complex genome, evolution is not only based on genome duplication with subsequent gene deletions and chromosomal rearrangements but also on fungi associated with specific environments (e.g. involving fungal-insect interactions as in Eremothecium), which have encountered challenges that may be reflected both in genome streamlining and their biosynthetic potential.

The Ashbya gossypii fimbrin SAC6 is required for fast polarized hyphal tip growth and endocytosis

Ashbya gossypii has been an ideal system to study filamentous hyphal growth. Previously, we identified a link between polarized hyphal growth, the organization of the actin cytoskeleton and endocytosis with our analysis of the A. gossypii Wiskott-Aldrich Syndrome Protein (WASP)-homolog encoded by the AgWAL1 gene. Here, we studied the role of AgSAC6, encoding a fimbrin in polarized hyphal growth and endocytosis, and based on our functional analysis identified genetic interactions between AgSAC6 and AgWAL1. SAC6 mutants show severely reduced polarized growth. This growth phenotype is temperature dependent and sac6 spores do not germinate at elevated temperatures. Spores germinated at 30°C generate slow growing mycelia without displaying polarity establishment defects at the hyphal tip. Several phenotypic characteristics of sac6 hyphae resemble those found in wal1 mutants. First, tips of sac6 hyphae shifted to 37°C swell and produce subapical bulges. Second, actin patches are mislocalized subapically. And third, the rate of endocytotic uptake of the vital dye FM4-64 was reduced. This indicates that actin filament bundling, a conserved function of fimbrins, is required for fast polarized hyphal growth, polarity maintenance, and endocytosis in filamentous fungi.

Candida albicans Vrp1 is required for polarized morphogenesis and interacts with Wal1 and Myo5

Recently, a link between endocytosis and hyphal morphogenesis has been identified in Candida albicans via the Wiskott–Aldrich syndrome gene homologue WAL1. To get a more detailed mechanistic understanding of this link we have investigated a potentially conserved interaction between Wal1 and the C. albicans WASP-interacting protein (WIP) homologue encoded by VRP1. Deletion of both alleles of VRP1 results in strong hyphal growth defects under serum inducing conditions but filamentation can be observed on Spider medium. Mutant vrp1 cells show a delay in endocytosis – measured as the uptake and delivery of the lipophilic dye FM4-64 into small endocytic vesicles – compared to the wild-type. Vacuolar morphology was found to be fragmented in a subset of cells and the cortical actin cytoskeleton was depolarized in vrp1 daughter cells. The morphology of the vrp1 null mutant could be complemented by reintegration of the wild-type VRP1 gene at the BUD3 locus. Using the yeast two-hybrid system we could demonstrate an interaction between the C-terminal part of Vrp1 and the N-terminal part of Wal1, which contains the WH1 domain. Furthermore, we found that Myo5 has several potential interaction sites on Vrp1. This suggests that a Wal1–Vrp1–Myo5 complex plays an important role in endocytosis and the polarized localization of the cortical actin cytoskeleton to promote polarized hyphal growth in C. albicans.

Candida albicans SH3-domain proteins involved in hyphal growth, cytokinesis, and vacuolar morphology

This report describes the analyses of three Candida albicans genes that encode Src Homology 3 (SH3)-domain proteins. Homologs in Saccharomyces cerevisiae are encoded by the SLA1, NBP2, and CYK3 genes. Deletion of CYK3 in C. albicans was not feasible, suggesting it is essential. Promoter shutdown experiments of CaCYK3 revealed cytokinesis defects, which are in line with the localization of GFP-tagged Cyk3 at septal sites. Deletion of SLA1 resulted in strains with decreased ability to form hyphal filaments. The number of cortical actin patches was strongly reduced in Deltasla1 strains during all growth stages. Sla1-GFP localizes in patches that are found concentrated at the hyphal tip. Deletion of the first two SH3-domains of Sla1 still resulted in cortical localization of the truncated protein. However, the actin cytoskeleton in this strain was aberrant like in the Deltasla1 deletion mutant indicating a function of these SH3 domains to recruit actin nucleation to sites of endocytosis. Deletion of NBP2 resulted in a defect in vacuolar fusion in hyphae. Germ cells of Deltanbp2 strains lacked a large vacuole but initiated several germ tubes. The mutant phenotypes of Deltanbp2 and Deltasla1 could be corrected by reintegration of the wild-type genes.

Analysis of flocculins in Ashbya gossypii reveals FIG2 regulation by TEC1

For 95% of the Ashbya gossypii protein-encoding genes there is a Saccharomyces cerevisiae homolog. Out of these 90% are arranged in a conserved, syntenic, gene order. Interestingly, A. gossypii adhesins, encoded by homologs of S. cerevisiae FLO-genes, are found in non-syntenic positions. A. gossypii contains only a small set of adhesins: two FLO5, a FLO11 and a FIG2 homolog, but no FLO1, FLO9, or FLO10 homolog. Here we present the functional analysis of the A. gossypii adhesins and their potential transcriptional regulators SFL1, FLO8, and TEC1. Deletion of individual classes of FLO-genes did not reveal any phenotype. Lack of SFL1 or FLO8 showed reduced growth. The expression of adhesins in different strain backgrounds was tested using promoter-lacZ-fusions. We found that SFL1 acts as a suppressor of one of the FLO5 genes and FLO8 but particularly of FIG2. Interestingly, FIG2 expression was abolished in a tec1 mutant. We identified three potential Tec1-binding sites in the FIG2-promoter by similarity to S. cerevisiae Tec1-binding sites. The AgCHT2 promoter, which regulates a sporulation specific chitinase, also harbours potential Tec1-binding sites. Consequently, expression of CHT2 was not detected in a tec1 strain. This suggests that Tec1- binding sites are conserved between A. gossypii and S. cerevisiae even though there are different Tec1 target genes in each of these organisms.

Forward genetics in Candida albicans that reveals the Arp2/3 complex is required for hyphal formation, but not endocytosis

Candida albicans is a diploid fungal pathogen lacking a defined complete sexual cycle, and thus has been refractory to standard forward genetic analysis. Instead, transcription profiling and reverse genetic strategies based on Saccharomyces cerevisiae have typically been used to link genes to functions. To overcome restrictions inherent in such indirect approaches, we have investigated a forward genetic mutagenesis strategy based on the UAU1 technology. We screened 4700 random insertion mutants for defects in hyphal development and linked two new genes (ARP2 and VPS52) to hyphal growth. Deleting ARP2 abolished hyphal formation, generated round and swollen yeast phase cells, disrupted cortical actin patches and blocked virulence in mice. The mutants also showed a global lack of induction of hyphae-specific genes upon the yeast-to-hyphae switch. Surprisingly, both arp2 Delta/Delta and arp2 Delta/Delta arp3 Delta/Delta mutants were still able to endocytose FM4-64 and Lucifer Yellow, although as shown by time-lapse movies internalization of FM4-64 was somewhat delayed in mutant cells. Thus the non-essential role of the Arp2/3 complex discovered by forward genetic screening in C. albicans showed that uptake of membrane components from the plasma membrane to vacuolar structures is not dependent on this actin nucleating machinery.

Comparative genomics of MAP kinase and calcium-calcineurin signalling components in plant and human pathogenic fungi

Mitogen-activated protein kinase (MAPK) cascades and the calcium-calcineurin pathway control fundamental aspects of fungal growth, development and reproduction. Core elements of these signalling pathways are required for virulence in a wide array of fungal pathogens of plants and mammals. In this review, we have used the available genome databases to explore the structural conservation of three MAPK cascades and the calcium-calcineurin pathway in ten different fungal species, including model organisms, plant pathogens and human pathogens. While most known pathway components from the model yeast Saccharomyces cerevisiae appear to be widely conserved among taxonomically and biologically diverse fungi, some of them were found to be restricted to the Saccharomycotina. The presence of multiple paralogues in certain species such as the zygomycete Rhizopus oryzae and the incorporation of new functional domains that are lacking in S. cerevisiae signalling proteins, most likely reflect functional diversification or adaptation as filamentous fungi have evolved to occupy distinct ecological niches.

Independent measurement of the total active 8B solar neutrino flux using an array of 3He proportional counters at the Sudbury Neutrino Observatory

The Sudbury Neutrino Observatory (SNO) used an array of 3He proportional counters to measure the rate of neutral-current interactions in heavy water and precisely determined the total active (nu_x) 8B solar neutrino flux. This technique is independent of previous methods employed by SNO. The total flux is found to be 5.54_-0.31;+0.33(stat)-0.34+0.36(syst)x10(6) cm(-2) s(-1), in agreement with previous measurements and standard solar models. A global analysis of solar and reactor neutrino results yields Deltam2=7.59_-0.21;+0.19x10(-5) eV2 and theta=34.4_-1.2;+1.3 degrees. The uncertainty on the mixing angle has been reduced from SNO's previous results.

Candida albicans Sfl1 suppresses flocculation and filamentation

Hyphal morphogenesis in Candida albicans is regulated by multiple pathways which act by either inducing or repressing filamentation. Most notably, Tup1, Nrg1, and Rfg1 are transcriptional repressors, while Efg1, Flo8, Cph1, and Czf1 can induce filamentation. Here, we present the functional analysis of CaSFL1, which encodes the C. albicans homolog of the Saccharomyces cerevisiae SFL1 (suppressor of flocculation) gene. Deletion of CaSFL1 results in flocculation (i.e., the formation of clumps) of yeast cells, which is most pronounced in minimal medium. The flocs contained hyphae already under noninducing conditions, and filamentation could be enhanced with hypha-inducing cues at 37 degrees C. Expression of SFL1 in a heterozygous mutant under the control of the CaMET3 promoter was shown to complement these defects and allowed switching between wild-type and mutant phenotypes. Interestingly, increased expression of SFL1 using a MET3prom-SFL1 construct prior to the induction of filamentation completely blocked germ tube formation. To localize Sfl1 in vivo, we generated a SFL1-GFP fusion. Sfl1-green fluorescent protein was found in the nucleus in both yeast cells and, to a lesser extent, hyphal cells. Using reverse transcription-PCR, we find an increased expression of ALS1, ALS3, HWP1, ECE1, and also FLO8. Our results suggest that Sfl1 functions in the repression of flocculation and filamentation and thus represents a novel negative regulator of C. albicans morphogenesis.

A molecular toolbox for manipulating Eremothecium coryli

The genus Eremothecium contains dimorphic and filamentous fungal species, most notably Eremothecium sinecaudum (Holleya sinecauda), a dimorphic plant pathogen, which was isolated from mustard seeds, and Eremothecium gossypii (Ashbya gossypii), a filamentous fungus, which is well known for its ability to produce riboflavin. In this study, we present the initial molecular characterization of another Eremothecium species classified as Eremothecium coryli. E.coryli is a dimorphic fungus. We have developed, based on previously described reagents, a transformation system for E. coryli using kanMX and NATMX3 as dominant selectable marker genes on freely replicating plasmids conferring resistance to the antibiotics G418 and nourseothricin, respectively. As reporter genes we could introduce lacZ and GFP, which were controlled either by the AgTEF1 promoter or by regulatable MET promoters derived from the A. gossypii and Saccharomyces cerevisiae MET3 genes. These newly established tools will allow a detailed comparison of different growth modes in filamentous or dimorphic species within the genus Eremothecium.