Saccharomyces cerevisiae derived postbiotic alters gut microbiome metabolism in the human distal colon resulting in immunomodulatory potential in vitro.

The yeast-based postbiotic EpiCor is a well-studied formulation, consisting of a complex mixture of bioactive molecules. In clinical studies, EpiCor postbiotic has been shown to reduce intestinal symptoms in a constipated population and support mucosal defense in healthy subjects. Anti-inflammatory potential and butyrogenic properties have been reported in vitro, suggesting a possible link between EpiCor's gut modulatory activity and immunomodulation. The current study used a standardized in vitro gut model, the Simulator of the Human Intestinal Microbial Ecosystem (SHIME®), to obtain a deeper understanding on host-microbiome interactions and potential microbiome modulation following repeated EpiCor administration. It was observed that EpiCor induced a functional shift in carbohydrate fermentation patterns in the proximal colon environment. Epicor promoted an increased abundance of Bifidobacterium in both the proximal and distal colon, affecting overall microbial community structure. Co-occurrence network analysis at the phylum level provided additional evidence of changes in the functional properties of microbial community promoted by EpiCor, increasing positive associations between Actinobacteria with microbes belonging to the Firmicutes phylum. These results, together with a significant increase in butyrate production provide additional support of EpiCor benefits to gut health. Investigation of host-microbiome interactions confirmed the immunomodulatory potential of the applied test product. Specific microbial alterations were observed in the distal colon, with metabotyping indicating that specific metabolic pathways, such as bile acid and tryptophan metabolism, were affected following EpiCor supplementation. These results, especially considering many effects were seen distally, further strengthen the position of EpiCor as a postbiotic with health promoting functionality in the gut, which could be further assessed in vivo.

Feeding Saccharomyces cerevisiae fermentation postbiotic products alters immune function and the lung transcriptome of preweaning calves with an experimental viral-bacterial coinfection.

Bovine respiratory disease causes morbidity and mortality in cattle of all ages. Supplementing with postbiotic products from Saccharomyces cerevisiae fermentation (SCFP) has been reported to improve growth and provide metabolic support required for immune activation in calves. The objective of this study was to determine effects of SCFP supplementation on the transcriptional response to coinfection with bovine respiratory syncytial virus (BRSV) and Pasteurella multocida in the lung using RNA sequencing. Twenty-three calves were enrolled and assigned to 2 treatment groups: control (n = 12) or SCFP-treated (n = 11, fed 1 g/d SmartCare in milk and 5 g/d NutriTek on starter grain; both from Diamond V Mills Inc.). Calves were infected with ∼104 median tissue culture infectious dose per milliliter of BRSV, followed 6 d later by intratracheal inoculation with ∼1010 cfu of Pasteurella multocida (strain P1062). Calves were euthanized on d 10 after viral infection. Blood cells were collected and assayed on d 0 and 10 after viral infection. Bronchoalveolar lavage (BAL) cells were collected and assayed on d 14 of the feeding period (preinfection) and d 10 after viral infection. Blood and BAL cells were assayed for proinflammatory cytokine production in response to stimulation with lipopolysaccharide (LPS) or a combination of polyinosinic:polycytidylic acid and imiquimod, and BAL cells were evaluated for phagocytic and reactive oxygen species production capacity. Antemortem and postmortem BAL and lesioned and nonlesioned lung tissue samples collected at necropsy were subjected to RNA extraction and sequencing. Sequencing reads were aligned to the bovine reference genome (UMD3.1) and edgeR version 3.32.1 used for differential gene expression analysis. Supplementation with SCFP did not affect the respiratory burst activity or phagocytic activity of either lung or blood immune cells. Immune cells from the peripheral blood of SCFP-supplemented calves produced increased quantities of IL-6 in response to toll-like receptor stimulation, whereas cells from the BAL of SCFP-treated calves secreted fewer proinflammatory cytokines and less tumor necrosis factor-α (TNF-α) and IL-6 in response to the same stimuli. Transcriptional responses in lung tissues and BAL samples from SCFP-fed calves differed from the control group. The top enriched pathways in SCFP-treated lungs were associated with decreased expression of inflammatory responses and increased expression of plasminogen and genes involved in glutathione metabolism, supporting effective lung repair. Our results indicate that supplementing with SCFP postbiotics modulates both systemic and mucosal immune responses, leading to increased resistance to bovine respiratory disease.

Multiempleo percepciones de médicos y enfermeros de la Provincia de Buenos Aires durante la pandemia por Covid-19 / Multi-employment perceptions of doctors and nurses in the Province of Buenos Aires during the Covid-19 pandemic

La situación de Multiempleo (ME) en Argentina, entendido como la combinación de la práctica clínica en una o más instituciones con la realización de otras actividades, es reconocida por diversos autores(MTEySS, 2021, OPS, 2013) y se ve favorecida por las características de un sistema de salud descentralizado y de tipología mixta.La pandemia COVID-19 incrementó la carga de trabajo y expuso la situación delME en los profesionales de salud. Para ahondar en su caracterización, se propuso un estudio en el ámbito de la PBA, que combinó diversas técnicas metodológicas. El presente trabajo incluye los resultados obtenidos en la fase cualitativa del estudio, que tuvo lugar en 2021.

The multi-employment (ME) situation in Argentina, understood as the clinical practice in one or more institutions combined with other activities, is recognized by various authors (MTEySS, 2021, OPS, 2013) and it is facilitated by the characteristics of a decentralized and mixed healthcare system. The COVID-19 pandemic increased workload and revealed the ME situation health professionals undergo. To delve deeper into this scenario, a study was conducted in the Buenos Aires province that combined different methodological techniques. This article includes the results obtained during the qualitative phase of the study, which took place in 2021.

Caracterización del multiempleo en salud entre médicos y enfermeros de la provincia de Buenos Aires un estudio transversal para el primer trimestre de 2021 / A cross-sectional study of physicians and nurses on multi-employment in healthcare during Q1 2021 in the province of Buenos Aires

Multiempleo (ME) y pluriempleo describen profesionales que combinan la práctica clínica con otras actividades, relacionadas o no con la atención de la salud. Entre los motivos que refieren para elegirlo se destacan la necesidad de aumentar los ingresos, la estabilidad y seguridad laboral, la búsqueda de prestigio, aprendizaje y diversificación de tareas. También influyen género, profesión o tipo de trabajo. La extensa jornada laboral resultante, el tiempo de traslado entre trabajos y las responsabilidades familiares dificultan la práctica e incrementan el cansancio de los profesionales.

Multi-employment (ME) and multiple employment describe professionals who combine clinical practice with other activities, whether related to healthcare or not. Among the reasons cited for this election are the need to increase income, job stability and security, the pursuit of prestige, learning, and diversification of tasks. Gender, profession, or type of job also influence this choice. The resulting extended workday, the time spent commuting between jobs, and family responsibilities hinder the practice and contribute to the professionals' fatigue

Multiempleo en salud en provincia de Buenos Aires: estudio transversal de profesiones afectadas al cuidado de pacientes con COVID-19 / Multi-employment in health in the province of Buenos Aires: cross-sectional study of professions involved in COVID-19 patient care

RESUMEN INTRODUCCIÓN La pandemia de COVID-19 expuso el impacto del multiempleo en los servicios de salud. El objetivo de este estudio fue caracterizar el multiempleo en médicos y enfermeros que trabajaron en internación general y cuidados críticos durante la pandemia en la provincia de Buenos Aires. MÉTODOS Se realizó un estudio exploratorio, descriptivo y transversal. Los datos se recolectaron en el primer trimestre de 2021 con una encuesta estructurada anónima autoadministrada mediante muestreo no probabilístico en cadena. RESULTADOS El 96,3% de los médicos y el 68,1% de los enfermeros declararon estar multiempleados. La media de empleos fue 3,1 para médicos (entre 1 y 5) y 1,9 para enfermeros (entre 1 y 3). Los enfermeros declararon trabajos con mayor carga horaria, predominio del empleo público y contratación estable. Los médicos multiempleados manifestaron mayor diversidad en la forma de contratación. En ambas profesiones el multiempleo es motivado principalmente por razones de índole económica. DISCUSIÓN El multiempleo es difícil de medir mediante los registros oficiales. La proporción de multiempleo autorreportado en este estudio supera las cifras comunicadas por las estadísticas e informes oficiales. Aun así, las diferencias halladas entre médicos y enfermeros respecto al número de empleos son coincidentes con estudios previos. El problema del multiempleo requiere ser abordado desde la desprecarización del empleo, con mejoras en las condiciones económicas y de trabajo.

ABSTRACT INTRODUCTION The COVID-19 pandemic exposed the impact of multi-employment in health services. The objective of this study was to characterize multi-employment among physicians and nurses working in general hospitalization and critical care during the pandemic in the province of Buenos Aires. METHODS An exploratory, descriptive, cross-sectional study was conducted. Data were collected in the first quarter of 2021 with a structured anonymous self-administered survey using non-probabilistic chain sampling. RESULTS A total of 96.3% of physicians and 68.1% of nurses reported being multi-employed. The mean number of jobs was 3.1 for physicians (between 1 and 5) and 1.9 for nurses (between 1 and 3). Nurses reported having jobs with longer hours, mostly public and stable employment. Multi-employed physicians reported greater variety in the form of hiring. In both professions, multi-employment is mainly motivated by economic reasons. DISCUSSION Multi-employment is difficult to measure through official records. The proportion of self-reported multiemployment in this study exceeds the figures shown by official statistics and reports. The differences found between physicians and nurses regarding the number of jobs are still consistent with previous studies. The problem of multi-employment needs to be tackled by making employment less precarious, with improvements in economic and working conditions.

Saccharomyces cerevisiae fermentation product improves robustness of equine gut microbiome upon stress.

Introduction: Nutritional and environmental stressors can disturb the gut microbiome of horses which may ultimately decrease their health and performance. We hypothesized that supplementation with a yeast-derived postbiotic (Saccharomyces cerevisiae fermentation product-SCFP) would benefit horses undergoing an established model of stress due to prolonged transportation. Methods: Quarter horses (n = 20) were blocked based on sex, age (22 ± 3 mo) and body weight (439 ± 3 kg) and randomized to receive either a basal diet of 60% hay and 40% concentrate (CON) or the basal diet supplemented with 21 g/d Diamond V TruEquine C (SCFP; Diamond V, Cedar Rapids, IA) for 60 days. On day 57, horses were tethered with their heads elevated 35cm above wither height for 12 h to induce mild upper respiratory tract inflammation. Fecal samples were collected at days 0, 28, and 56 before induction of stress, and at 0, 12, 24, and 72 h post-stress and subjected to DNA extraction and Nanopore shotgun metagenomics. Within sample (alpha) diversity was evaluated by fitting a linear model and between sample (beta) diversity was tested with permutational ANOVA. Results: The SCFP stabilized alpha diversity across all time points, whereas CON horses had more fluctuation (P < 0.05) at 12, 24, and 72 h post-challenge compared to d 56. A significant difference between CON and SCFP was observed at 0 and 12 h. There was no difference in beta-diversity between SCFP and CON on d 56. Discussion: Taken together, these observations led us to conclude that treatment with SCFP resulted in more robust and stable microbial profiles in horses after stress challenge.

El multiempleo en profesionales de la salud de la Provincia de Buenos Aires: estudio transversal de profesiones y especialidades más demandadas en la pandemia COVID-19 / Multi-employment in health professionals in the Province of Buenos Aires: cross-sectional study of professions and specialties most in demand in the COVID-19 pandemic

INTRODUCCIÓN La pandemia COVID-19 incrementó la carga de trabajo y expuso el impacto del multiempleo en los servicios de salud. El presente estudio busca caracterizar el multiempleo entre profesionales médicos y de enfermería que trabajaron en internación clínica y cuidados críticos durante la pandemia en la provincia de Buenos Aires (PBA). METODOS Se realizó un estudio exploratorio, descriptivo y transversal, mediante técnicas cuantitativas y cualitativas que combinaron fuentes primarias (encuesta estructurada, entrevistas) y secundarias (bases de datos de recursos humanos). RESULTADOS El cruce de datos arrojó un multiempleo explícito del 12,7% en enfermería y 28,3% en medicina. En la encuesta, 96,3% de médicos y 68,1% de enfermeros declara multiempleo. La media de empleos fue 3,1 para médicos y 1,89 para enfermeros. Los motivos más frecuentes de multiempleo son la subsistencia y el incremento de ingresos. En condiciones adecuadas, el 90% optaría por un empleo, principalmente mujeres y jóvenes. El hospital público surge como el ámbito elegido. No hay coincidencias ni confianza en lograr empleo único. DISCUSIÓN El multiempleo en PBA es difícil de medir mediante los registros vigentes y difiere de los datos auto informados. El problema del multiempleo requiere ser abordado desde la desprecarización del empleo, con perspectiva de género y mejoras en las condiciones económicas y de trabajo.

Genotype-by-Environment-by-Environment Interactions in the Saccharomyces cerevisiae Transcriptomic Response to Alcohols and Anaerobiosis.

Next generation biofuels including longer-chain alcohols such as butanol are attractive as renewable, high-energy fuels. A barrier to microbial production of butanols is the increased toxicity compared to ethanol; however, the cellular targets and microbial defense mechanisms remain poorly understood, especially under anaerobic conditions used frequently in industry. Here we took a comparative approach to understand the response of Saccharomyces cerevisiae to 1-butanol, isobutanol, or ethanol, across three genetic backgrounds of varying tolerance in aerobic and anaerobic conditions. We find that strains have different growth properties and alcohol tolerances with and without oxygen availability, as well as unique and common responses to each of the three alcohols. Our results provide evidence for strain-by-alcohol-by-oxygen interactions that moderate how cells respond to alcohol stress.

Natural Variation in the Multidrug Efflux Pump SGE1 Underlies Ionic Liquid Tolerance in Yeast.

Imidazolium ionic liquids (IILs) have a range of biotechnological applications, including as pretreatment solvents that extract cellulose from plant biomass for microbial fermentation into sustainable bioenergy. However, residual levels of IILs, such as 1-ethyl-3-methylimidazolium chloride ([C2C1im]Cl), are toxic to biofuel-producing microbes, including the yeast Saccharomyces cerevisiae. S. cerevisiae strains isolated from diverse ecological niches differ in genomic sequence and in phenotypes potentially beneficial for industrial applications, including tolerance to inhibitory compounds present in hydrolyzed plant feedstocks. We evaluated >100 genome-sequenced S. cerevisiae strains for tolerance to [C2C1im]Cl and identified one strain with exceptional tolerance. By screening a library of genomic DNA fragments from the [C2C1im]Cl-tolerant strain for improved IIL tolerance, we identified SGE1, which encodes a plasma membrane multidrug efflux pump, and a previously uncharacterized gene that we named ionic liquid tolerance 1 (ILT1), which encodes a predicted membrane protein. Analyses of SGE1 sequences from our panel of S. cerevisiae strains together with growth phenotypes implicated two single nucleotide polymorphisms (SNPs) that associated with IIL tolerance and sensitivity. We confirmed these phenotypic effects by transferring the SGE1 SNPs into a [C2C1im]Cl-sensitive yeast strain using CRISPR/Cas9 genome editing. Further studies indicated that these SNPs affect Sge1 protein stability and cell surface localization, influencing the amount of toxic IILs that cells can pump out of the cytoplasm. Our results highlight the general potential for discovering useful biotechnological functions from untapped natural sequence variation and provide functional insight into emergent SGE1 alleles with reduced capacities to protect against IIL toxicity.

Genetic background effects in quantitative genetics: gene-by-system interactions.

Proper cell function depends on networks of proteins that interact physically and functionally to carry out physiological processes. Thus, it seems logical that the impact of sequence variation in one protein could be significantly influenced by genetic variants at other loci in a genome. Nonetheless, the importance of such genetic interactions, known as epistasis, in explaining phenotypic variation remains a matter of debate in genetics. Recent work from our lab revealed that genes implicated from an association study of toxin tolerance in Saccharomyces cerevisiae show extensive interactions with the genetic background: most implicated genes, regardless of allele, are important for toxin tolerance in only one of two tested strains. The prevalence of background effects in our study adds to other reports of widespread genetic-background interactions in model organisms. We suggest that these effects represent many-way interactions with myriad features of the cellular system that vary across classes of individuals. Such gene-by-system interactions may influence diverse traits and require new modeling approaches to accurately represent genotype-phenotype relationships across individuals.

Genome-wide association across Saccharomyces cerevisiae strains reveals substantial variation in underlying gene requirements for toxin tolerance.

Cellulosic plant biomass is a promising sustainable resource for generating alternative biofuels and biochemicals with microbial factories. But a remaining bottleneck is engineering microbes that are tolerant of toxins generated during biomass processing, because mechanisms of toxin defense are only beginning to emerge. Here, we exploited natural diversity in 165 Saccharomyces cerevisiae strains isolated from diverse geographical and ecological niches, to identify mechanisms of hydrolysate-toxin tolerance. We performed genome-wide association (GWA) analysis to identify genetic variants underlying toxin tolerance, and gene knockouts and allele-swap experiments to validate the involvement of implicated genes. In the process of this work, we uncovered a surprising difference in genetic architecture depending on strain background: in all but one case, knockout of implicated genes had a significant effect on toxin tolerance in one strain, but no significant effect in another strain. In fact, whether or not the gene was involved in tolerance in each strain background had a bigger contribution to strain-specific variation than allelic differences. Our results suggest a major difference in the underlying network of causal genes in different strains, suggesting that mechanisms of hydrolysate tolerance are very dependent on the genetic background. These results could have significant implications for interpreting GWA results and raise important considerations for engineering strategies for industrial strain improvement.

Incorporating comparative genomics into the design-test-learn cycle of microbial strain engineering.

Engineering microbes with new properties is an important goal in industrial engineering, to establish biological factories for production of biofuels, commodity chemicals and pharmaceutics. But engineering microbes to produce new compounds with high yield remains a major challenge toward economically viable production. Incorporating several modern approaches, including synthetic and systems biology, metabolic modeling and regulatory rewiring, has proven to significantly advance industrial strain engineering. This review highlights how comparative genomics can also facilitate strain engineering, by identifying novel genes and pathways, regulatory mechanisms and genetic background effects for engineering. We discuss how incorporating comparative genomics into the design-test-learn cycle of strain engineering can provide novel information that complements other engineering strategies.

Hybridization and adaptive evolution of diverse Saccharomyces species for cellulosic biofuel production.

BACKGROUND: Lignocellulosic biomass is a common resource across the globe, and its fermentation offers a promising option for generating renewable liquid transportation fuels. The deconstruction of lignocellulosic biomass releases sugars that can be fermented by microbes, but these processes also produce fermentation inhibitors, such as aromatic acids and aldehydes. Several research projects have investigated lignocellulosic biomass fermentation by the baker's yeast Saccharomyces cerevisiae. Most projects have taken synthetic biological approaches or have explored naturally occurring diversity in S. cerevisiae to enhance stress tolerance, xylose consumption, or ethanol production. Despite these efforts, improved strains with new properties are needed. In other industrial processes, such as wine and beer fermentation, interspecies hybrids have combined important traits from multiple species, suggesting that interspecies hybridization may also offer potential for biofuel research. RESULTS: To investigate the efficacy of this approach for traits relevant to lignocellulosic biofuel production, we generated synthetic hybrids by crossing engineered xylose-fermenting strains of S. cerevisiae with wild strains from various Saccharomyces species. These interspecies hybrids retained important parental traits, such as xylose consumption and stress tolerance, while displaying intermediate kinetic parameters and, in some cases, heterosis (hybrid vigor). Next, we exposed them to adaptive evolution in ammonia fiber expansion-pretreated corn stover hydrolysate and recovered strains with improved fermentative traits. Genome sequencing showed that the genomes of these evolved synthetic hybrids underwent rearrangements, duplications, and deletions. To determine whether the genus Saccharomyces contains additional untapped potential, we screened a genetically diverse collection of more than 500 wild, non-engineered Saccharomyces isolates and uncovered a wide range of capabilities for traits relevant to cellulosic biofuel production. Notably, Saccharomyces mikatae strains have high innate tolerance to hydrolysate toxins, while some Saccharomyces species have a robust native capacity to consume xylose. CONCLUSIONS: This research demonstrates that hybridization is a viable method to combine industrially relevant traits from diverse yeast species and that members of the genus Saccharomyces beyond S. cerevisiae may offer advantageous genes and traits of interest to the lignocellulosic biofuel industry.

Correction: Directed Evolution Reveals Unexpected Epistatic Interactions That Alter Metabolic Regulation and Enable Anaerobic Xylose Use by Saccharomyces cerevisiae.

[This corrects the article DOI: 10.1371/journal.pgen.1006372.].

Directed Evolution Reveals Unexpected Epistatic Interactions That Alter Metabolic Regulation and Enable Anaerobic Xylose Use by Saccharomyces cerevisiae.

The inability of native Saccharomyces cerevisiae to convert xylose from plant biomass into biofuels remains a major challenge for the production of renewable bioenergy. Despite extensive knowledge of the regulatory networks controlling carbon metabolism in yeast, little is known about how to reprogram S. cerevisiae to ferment xylose at rates comparable to glucose. Here we combined genome sequencing, proteomic profiling, and metabolomic analyses to identify and characterize the responsible mutations in a series of evolved strains capable of metabolizing xylose aerobically or anaerobically. We report that rapid xylose conversion by engineered and evolved S. cerevisiae strains depends upon epistatic interactions among genes encoding a xylose reductase (GRE3), a component of MAP Kinase (MAPK) signaling (HOG1), a regulator of Protein Kinase A (PKA) signaling (IRA2), and a scaffolding protein for mitochondrial iron-sulfur (Fe-S) cluster biogenesis (ISU1). Interestingly, the mutation in IRA2 only impacted anaerobic xylose consumption and required the loss of ISU1 function, indicating a previously unknown connection between PKA signaling, Fe-S cluster biogenesis, and anaerobiosis. Proteomic and metabolomic comparisons revealed that the xylose-metabolizing mutant strains exhibit altered metabolic pathways relative to the parental strain when grown in xylose. Further analyses revealed that interacting mutations in HOG1 and ISU1 unexpectedly elevated mitochondrial respiratory proteins and enabled rapid aerobic respiration of xylose and other non-fermentable carbon substrates. Our findings suggest a surprising connection between Fe-S cluster biogenesis and signaling that facilitates aerobic respiration and anaerobic fermentation of xylose, underscoring how much remains unknown about the eukaryotic signaling systems that regulate carbon metabolism.

Leveraging Genetic-Background Effects in Saccharomyces cerevisiae To Improve Lignocellulosic Hydrolysate Tolerance.

UNLABELLED: A major obstacle to sustainable lignocellulosic biofuel production is microbe inhibition by the combinatorial stresses in pretreated plant hydrolysate. Chemical biomass pretreatment releases a suite of toxins that interact with other stressors, including high osmolarity and temperature, which together can have poorly understood synergistic effects on cells. Improving tolerance in industrial strains has been hindered, in part because the mechanisms of tolerance reported in the literature often fail to recapitulate in other strain backgrounds. Here, we explored and then exploited variations in stress tolerance, toxin-induced transcriptomic responses, and fitness effects of gene overexpression in different Saccharomyces cerevisiae (yeast) strains to identify genes and processes linked to tolerance of hydrolysate stressors. Using six different S. cerevisiae strains that together maximized phenotypic and genetic diversity, first we explored transcriptomic differences between resistant and sensitive strains to identify common and strain-specific responses. This comparative analysis implicated primary cellular targets of hydrolysate toxins, secondary effects of defective defense strategies, and mechanisms of tolerance. Dissecting the responses to individual hydrolysate components across strains pointed to synergistic interactions between osmolarity, pH, hydrolysate toxins, and nutrient composition. By characterizing the effects of high-copy gene overexpression in three different strains, we revealed the breadth of the background-specific effects of gene fitness contributions in synthetic hydrolysate. Our approach identified new genes for engineering improved stress tolerance in diverse strains while illuminating the effects of genetic background on molecular mechanisms. IMPORTANCE: Recent studies on natural variation within Saccharomyces cerevisiae have uncovered substantial phenotypic diversity. Here, we took advantage of this diversity, using it as a tool to infer the effects of combinatorial stress found in lignocellulosic hydrolysate. By comparing sensitive and tolerant strains, we implicated primary cellular targets of hydrolysate toxins and elucidated the physiological states of cells when exposed to this stress. We also explored the strain-specific effects of gene overexpression to further identify strain-specific responses to hydrolysate stresses and to identify genes that improve hydrolysate tolerance independent of strain background. This study underscores the importance of studying multiple strains to understand the effects of hydrolysate stress and provides a method to find genes that improve tolerance across strain backgrounds.

Genome Sequence and Analysis of a Stress-Tolerant, Wild-Derived Strain of Saccharomyces cerevisiae Used in Biofuels Research.

The genome sequences of more than 100 strains of the yeast Saccharomyces cerevisiae have been published. Unfortunately, most of these genome assemblies contain dozens to hundreds of gaps at repetitive sequences, including transposable elements, tRNAs, and subtelomeric regions, which is where novel genes generally reside. Relatively few strains have been chosen for genome sequencing based on their biofuel production potential, leaving an additional knowledge gap. Here, we describe the nearly complete genome sequence of GLBRCY22-3 (Y22-3), a strain of S. cerevisiae derived from the stress-tolerant wild strain NRRL YB-210 and subsequently engineered for xylose metabolism. After benchmarking several genome assembly approaches, we developed a pipeline to integrate Pacific Biosciences (PacBio) and Illumina sequencing data and achieved one of the highest quality genome assemblies for any S. cerevisiae strain. Specifically, the contig N50 is 693 kbp, and the sequences of most chromosomes, the mitochondrial genome, and the 2-micron plasmid are complete. Our annotation predicts 92 genes that are not present in the reference genome of the laboratory strain S288c, over 70% of which were expressed. We predicted functions for 43 of these genes, 28 of which were previously uncharacterized and unnamed. Remarkably, many of these genes are predicted to be involved in stress tolerance and carbon metabolism and are shared with a Brazilian bioethanol production strain, even though the strains differ dramatically at most genetic loci. The Y22-3 genome sequence provides an exceptionally high-quality resource for basic and applied research in bioenergy and genetics.

Further support for aneuploidy tolerance in wild yeast and effects of dosage compensation on gene copy-number evolution.

In our prior work by Hose et al., we performed a genome-sequencing survey and reported that aneuploidy was frequently observed in wild strains of S. cerevisiae. We also profiled transcriptome abundance in naturally aneuploid isolates compared to isogenic euploid controls and found that 10-30% of amplified genes, depending on the strain and affected chromosome, show lower-than-expected expression compared to gene copy number. In Hose et al., we argued that this gene group is enriched for genes subject to one or more modes of dosage compensation, where mRNA abundance is decreased in response to higher dosage of that gene. A recent manuscript by Torres et al. refutes our prior work. Here, we provide a response to Torres et al., along with additional analysis and controls to support our original conclusions. We maintain that aneuploidy is well tolerated in the wild strains of S. cerevisiae that we studied and that the group of genes enriched for those subject to dosage compensation show unique evolutionary signatures.

Dosage compensation can buffer copy-number variation in wild yeast.

Aneuploidy is linked to myriad diseases but also facilitates organismal evolution. It remains unclear how cells overcome the deleterious effects of aneuploidy until new phenotypes evolve. Although laboratory strains are extremely sensitive to aneuploidy, we show here that aneuploidy is common in wild yeast isolates, which show lower-than-expected expression at many amplified genes. We generated diploid strain panels in which cells carried two, three, or four copies of the affected chromosomes, to show that gene-dosage compensation functions at >30% of amplified genes. Genes subject to dosage compensation are under higher expression constraint in wild populations-but they show elevated rates of gene amplification, suggesting that copy-number variation is buffered at these genes. We find that aneuploidy provides a clear ecological advantage to oak strain YPS1009, by amplifying a causal gene that escapes dosage compensation. Our work presents a model in which dosage compensation buffers gene amplification through aneuploidy to provide a natural, but likely transient, route to rapid phenotypic evolution.