| 1. |
- Carmona-Gutierrez, D., et al.
(författare)
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Guidelines and recommendations on yeast cell death nomenclature
- 2018
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Ingår i: Microbial Cell. - : Shared Science Publishers OG. - 2311-2638. ; 5:1, s. 4-31
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Forskningsöversikt (refereegranskat)abstract
- Elucidating the biology of yeast in its full complexity has major implications for science, medicine and industry. One of the most critical processes determining yeast life and physiology is cellular demise. However, the investigation of yeast cell death is a relatively young field, and a widely accepted set of concepts and terms is still missing. Here, we propose unified criteria for the definition of accidental, regulated, and programmed forms of cell death in yeast based on a series of morphological and biochemical criteria. Specifically, we provide consensus guidelines on the differential definition of terms including apoptosis, regulated necrosis, and autophagic cell death, as we refer to additional cell death routines that are relevant for the biology of (at least some species of) yeast. As this area of investigation advances rapidly, changes and extensions to this set of recommendations will be implemented in the years to come. Nonetheless, we strongly encourage the authors, reviewers and editors of scientific articles to adopt these collective standards in order to establish an accurate framework for yeast cell death research and, ultimately, to accelerate the progress of this vibrant field of research.
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| 2. |
- Tamás, Markus J., 1970, et al.
(författare)
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A Short Regulatory Domain Restricts Glycerol Transport through Yeast Fps1p
- 2003
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Ingår i: J. Biol. Chem. ; 278, s. 6337-6345
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Tidskriftsartikel (refereegranskat)abstract
- The controlled export of solutes is crucial for cellular adaptation to hypotonic conditions. In the yeast Saccharomyces cerevisiae glycerol export is mediated by Fps1p, a member of the major intrinsic protein (MIP) family of channel proteins. Here we describe a short regulatory domain that restricts glycerol transport through Fps1p. This domain is required for retention of cellular glycerol under hypertonic stress and hence acquisition of osmotolerance. It is located in the N-terminal cytoplasmic extension close to the first transmembrane domain. Several residues within that domain and its precise position are critical for channel control while the proximal residues 13-215 of the N-terminal extension are not required. The sequence of the regulatory domain and its position are perfectly conserved in orthologs from other yeast species. The regulatory domain has an amphiphilic character, and structural predictions indicate that it could fold back into the membrane bilayer. Remarkably, this domain has structural similarity to the channel forming loops B and E of Fps1p and other glycerol facilitators. Intragenic second-site suppressor mutations of the sensitivity to high osmolarity conferred by truncation of the regulatory domain caused diminished glycerol transport, confirming that elevated channel activity is the cause of the osmosensitive phenotype.
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| 3. |
- Tamás, Markus J., 1970, et al.
(författare)
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Fps1p controls the accumulation and release of the compatible solute glycerol in yeast osmoregulation.
- 1999
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Ingår i: Molecular microbiology. - 0950-382X .- 1365-2958. ; 4, s. 1087-104
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Tidskriftsartikel (refereegranskat)abstract
- The accumulation of compatible solutes, such as glycerol, in the yeast Saccharomyces cerevisiae, is a ubiquitous mechanism in cellular osmoregulation. Here, we demonstrate that yeast cells control glycerol accumulation in part via a regulated, Fps1p-mediated export of glycerol. Fps1p is a member of the MIP family of channel proteins most closely related to the bacterial glycerol facilitators. The protein is localized in the plasma membrane. The physiological role of Fps1p appears to be glycerol export rather than uptake. Fps1 delta mutants are sensitive to hypo-osmotic shock, demonstrating that osmolyte export is required for recovery from a sudden drop in external osmolarity. In wild-type cells, the glycerol transport rate is decreased by hyperosmotic shock and increased by hypo-osmotic shock on a subminute time scale. This regulation seems to be independent of the known yeast osmosensing HOG and PKC signalling pathways. Mutants lacking the unique hydrophilic N-terminal domain of Fps1p, or certain parts thereof, fail to reduce the glycerol transport rate after a hyperosmotic shock. Yeast cells carrying these constructs constitutively release glycerol and show a dominant hyperosmosensitivity, but compensate for glycerol loss after prolonged incubation by glycerol overproduction. Fps1p may be an example of a more widespread class of regulators of osmoadaptation, which control the cellular content and release of compatible solutes.
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| 4. |
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| 5. |
- Mukherjee, Vaskar, 1986, et al.
(författare)
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Phenotypic landscape of non-conventional yeast species for different stress tolerance traits desirable in bioethanol fermentation
- 2017
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 10
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Tidskriftsartikel (refereegranskat)abstract
- Background: Non-conventional yeasts present a huge, yet barely exploited, resource of yeast biodiversity for industrial applications. This presents a great opportunity to explore alternative ethanol-fermenting yeasts that are more adapted to some of the stress factors present in the harsh environmental conditions in second-generation (2G) bioethanol fermentation. Extremely tolerant yeast species are interesting candidates to investigate the underlying tolerance mechanisms and to identify genes that when transferred to existing industrial strains could help to design more stress-tolerant cell factories. For this purpose, we performed a high-throughput phenotypic evaluation of a large collection of non-conventional yeast species to identify the tolerance limits of the different yeast species for desirable stress tolerance traits in 2G bioethanol production. Next, 12 multi-tolerant strains were selected and used in fermentations under different stressful conditions. Five strains out of which, showing desirable fermentation characteristics, were then evaluated in small-scale, semi-anaerobic fermentations with lignocellulose hydrolysates. Results: Our results revealed the phenotypic landscape of many non-conventional yeast species which have not been previously characterized for tolerance to stress conditions relevant for bioethanol production. This has identified for each stress condition evaluated several extremely tolerant non-Saccharomyces yeasts. It also revealed multitolerance in several yeast species, which makes those species good candidates to investigate the molecular basis of a robust general stress tolerance. The results showed that some non-conventional yeast species have similar or even better fermentation efficiency compared to S. cerevisiae in the presence of certain stressful conditions. Conclusion: Prior to this study, our knowledge on extreme stress-tolerant phenotypes in non-conventional yeasts was limited to only few species. Our work has now revealed in a systematic way the potential of non-Saccharomyces species to emerge either as alternative host species or as a source of valuable genetic information for construction of more robust industrial S. serevisiae bioethanol production yeasts. Striking examples include yeast species like Pichia kudriavzevii and Wickerhamomyces anomalus that show very high tolerance to diverse stress factors. This large-scale phenotypic analysis has yielded a detailed database useful as a resource for future studies to understand and benefit from the molecular mechanisms underlying the extreme phenotypes of non-conventional yeast species.
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| 6. |
- Ansell, R, et al.
(författare)
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The two isoenzymes for yeast NAD+-dependent glycerol 3-phosphate dehydrogenase encoded by GPD1 and GPD2 have distinct roles in osmoadaptation and redox regulation.
- 1997
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Ingår i: The EMBO journal. - : Wiley. - 0261-4189 .- 1460-2075. ; 16:9, s. 2179-87
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Tidskriftsartikel (refereegranskat)abstract
- The two homologous genes GPD1 and GPD2 encode the isoenzymes of NAD-dependent glycerol 3-phosphate dehydrogenase in the yeast Saccharomyces cerevisiae. Previous studies showed that GPD1 plays a role in osmoadaptation since its expression is induced by osmotic stress and gpd1 delta mutants are osmosensitive. Here we report that GPD2 has an entirely different physiological role. Expression of GPD2 is not affected by changes in external osmolarity, but is stimulated by anoxic conditions. Mutants lacking GPD2 show poor growth under anaerobic conditions. Mutants deleted for both GPD1 and GPD2 do not produce detectable glycerol, are highly osmosensitive and fail to grow under anoxic conditions. This growth inhibition, which is accompanied by a strong intracellular accumulation of NADH, is relieved by external addition of acetaldehyde, an effective oxidizer of NADH. Thus, glycerol formation is strictly required as a redox sink for excess cytosolic NADH during anaerobic metabolism. The anaerobic induction of GPD2 is independent of the HOG pathway which controls the osmotic induction of GPD1. Expression of GPD2 is also unaffected by ROX1 and ROX3, encoding putative regulators of hypoxic and stress-controlled gene expression. In addition, GPD2 is induced under aerobic conditions by the addition of bisulfite which causes NADH accumulation by inhibiting the final, reductive step in ethanol fermentation and this induction is reversed by addition of acetaldehyde. We conclude that expression of GPD2 is controlled by a novel, oxygen-independent, signalling pathway which is required to regulate metabolism under anoxic conditions.
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| 7. |
- Holt, Sylvester, et al.
(författare)
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Bioflavoring by non-conventional yeasts in sequential beer fermentations
- 2018
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Ingår i: Food Microbiology. - : Elsevier BV. - 0740-0020 .- 1095-9998. ; 72, s. 55-66
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Tidskriftsartikel (refereegranskat)abstract
- Non-conventional yeast species have great capacity for producing diverse flavor profiles in production of alcoholic beverages, but their potential for beer brewing, in particular in consecutive fermentations with Saccharomyces cerevisiae, has only poorly been explored. We have screened 17 non-conventional yeast species for production of an appealing profile of flavor esters and phenolics in the first phase of alcoholic fermentation, followed by inoculation with S. cerevisiae to complete the fermentation. For measurement of phenolic compoundsand their precursors we developed an improved and highly sensitive methodology. The results show that non-conventional yeast species possess promising potential for enhancement of desirable flavors in beer production. Notable examples are increasing isoamyl acetate (fruity, banana flavor) by application of P. kluyverii, augmenting ethyl phenolic compounds (spicy notes) with Brettanomycesspecies and enhancing 4-vinyl guaiacol (clove-like aroma) with T. delbrueckii. All Pichia strains also produced high levels of ethyl acetate (solvent-like flavor). This might be selectively counteracted by selection of an appropriate S. cerevisiae strain for the second fermentation phase, which lowers total ester profile. Hence, optimization of the process conditions and/or proper strain selection in sequentially inoculated fermentations are required to unlock the full potential for aroma improvement by the non-conventional yeast species.
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| 8. |
- Mukherjee, Vaskar, 1986, et al.
(författare)
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High throughput screening of yeast strains for desirable stress tolerant traits for bioethanol production
- 2013
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Ingår i: Yeast. - : Wiley. - 0749-503X.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Implementation of very high gravity (VHG) fermentation technology in second generation bioethanol production using raw lignocellulosic biomass is fundamental to establish a commercially viable plant. However, so far the application of this technology is greatly restricted by the unavailability of a fermentative microorganism, resistant enough to the wide variety of stressors commonly encountered in VHG fermentation. In addition, the appropriate tools and knowledge to select such multi-stress tolerant microorganisms and to make a scientifically proven choice of the appropriate candidate strains have been lacking until recently. In this study we screened a large yeast culture collection, consisting of about 700 Saccharomyces cerevisiae and non-Saccharomyces strains from diverse origins, for different desirable traits for bioethanol production. These included, for example, osmotolerance, halotolerance, ethanol tolerance, thermotolerance, and tolerance against fermentation inhibitors like furfural and hydroxymethyl furfural as well as some heavy metals. To this end, a high throughput semi-automated robot was used for spotting up to 96 strains per screening plate. After incubation, plates were scanned and growth was recorded and analyzed using dedicated software. Cluster analysis showed clear differences in tolerance among species and among strains of the same species. In addition, strains showing co-tolerance against different traits could be identified. As such, our study enabled to efficiently select top candidate strains having desirable traits for VHG bioethanol production.
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| 9. |
- Mukherjee, Vaskar, 1986, et al.
(författare)
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Phenotypic evaluation of natural and industrial Saccharomyces yeasts for different traits desirable in industrial bioethanol production
- 2014
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 98:9483
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Tidskriftsartikel (refereegranskat)abstract
- Saccharomyces cerevisiae is the organism of choice for many food and beverage fermentations because it thrives in high-sugar and high-ethanol conditions. However, the conditions encountered in bioethanol fermentation pose specific challenges, including extremely high sugar and ethanol concentrations, high temperature, and the presence of specific toxic compounds. It is generally considered that exploring the natural biodiversity of Saccharomyces strains may be an interesting route to find superior bioethanol strains and may also improve our understanding of the challenges faced by yeast cells during bioethanol fermentation. In this study, we phenotypically evaluated a large collection of diverse Saccharomyces strains on six selective traits relevant for bioethanol production with increasing stress intensity. Our results demonstrate a remarkably large phenotypic diversity among different Saccharomyces species and among S. cerevisiae strains from different origins. Currently applied bioethanol strains showed a high tolerance to many of these relevant traits, but several other natural and industrial S. cerevisiae strains outcompeted the bioethanol strains for specific traits. These multitolerant strains performed well in fermentation experiments mimicking industrial bioethanol production. Together, our results illustrate the potential of phenotyping the natural biodiversity of yeasts to find superior industrial strains that may be used in bioethanol production or can be used as a basis for further strain improvement through genetic engineering, experimental evolution, or breeding. Additionally, our study provides a basis for new insights into the relationships between tolerance to different stressors.
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| 10. |
- Mukherjee, Vaskar, 1986, et al.
(författare)
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Polygenic analysis of high osmotolerance in Saccharomyces cerevisiae
- 2015
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Ingår i: Abstracts of the 27th International Conference on Yeast Genetics and Molecular Biology. - : Wiley. ; 32:S1
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The main objective of our research is to investigate the molecular basis of superior osmotolerance in Saccharomyces cerevisiae and to identify unique mutations in the causative genes that are responsible for superior fermentation performance under very high gravity fermentation. We employed pooled-segregant whole-genome sequence analysis, a technology for efficient polygenic analysis of complex traits developed in our laboratory. For that purpose, a haploid segregant of an osmotolerant yeast strain with the best superior phenotype has been crossed with a haploid segregant from an unrelated industrial strain with a comparatively inferior phenotype. The diploid hybrid has been sporulated and about 30 segregants with the superior phenotype have been selected to construct the superior pool. About 30 segregants were also randomly selected regardless of their phenotype to construct the unselected pool. Pooled genomic DNA extraction was performed for both pools separately and submitted to custom whole-genome sequence analysis. The two parent strains have also been sent for sequencing to determine all SNPs. The variant frequency of the SNPs in the pool has been used to map the QTLs containing the causative mutations in the genome. Several clear QTLs with different strength have been identified in this way. This is followed by the application of reciprocal hemizygosity analysis to identify the causative gene(s) with the responsible mutation in the mapped loci. Finally the identified causative mutations will be introduced in to industrial strains to improve the very high gravity bioethanol fermentation performance.
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