Yeast
Yeasts are very versatile, model unicellular eukaryotes that have been extensively used for over a century to explore fundamental aspects of living systems. This collection brings together the latest studies showcasing research on biotechnological applications of yeasts, yeasts as disease models, and pathogenic yeasts.
Collection Contents
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Identification of a novel gene required for competitive growth at high temperature in the thermotolerant yeast Kluyveromyces marxianus
It is important to understand the basis of thermotolerance in yeasts to broaden their application in industrial biotechnology. The capacity to run bioprocesses at temperatures above 40 °C is of great interest but this is beyond the growth range of most of the commonly used yeast species. In contrast, some industrial yeasts such as Kluyveromyces marxianus can grow at temperatures of 45 °C or higher. Such species are valuable for direct use in industrial biotechnology and as a vehicle to study the genetic and physiological basis of yeast thermotolerance. In previous work, we reported that evolutionarily young genes disproportionately changed expression when yeast were growing under stressful conditions and postulated that such genes could be important for long-term adaptation to stress. Here, we tested this hypothesis in K. marxianus by identifying and studying species-specific genes that showed increased expression during high-temperature growth. Twelve such genes were identified and 11 were successfully inactivated using CRISPR-mediated mutagenesis. One gene, KLMX_70384, is required for competitive growth at high temperature, supporting the hypothesis that evolutionary young genes could play roles in adaptation to harsh environments. KLMX_70384 is predicted to encode an 83 aa peptide, and RNA sequencing and ribo-sequencing were used to confirm transcription and translation of the gene. The precise function of KLMX_70384 remains unknown but some features are suggestive of RNA-binding activity. The gene is located in what was previously considered an intergenic region of the genome, which lacks homologues in other yeasts or in databases. Overall, the data support the hypothesis that genes that arose de novo in K. marxianus after the speciation event that separated K. marxianus and K. lactis contribute to some of its unique traits.
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The impact of the absence of Toll-like receptor-2 during Sporothrix brasiliensis infection
More LessPurpose. Sporothrix brasiliensis, a member of the Sporothrix schenckii complex, is a major cause of epidemic outbreaks of sporotrichosis due to its greater virulence and ability to evade the immune system. The absence of studies about this species led to this study, with the aim to evaluate the importance of Toll-like receptor-2 (TLR-2) during S. brasiliensis infection.
Methodology. In vitro assays were performed using bone marrow-derived macrophages from both wild-type (C57BL/6) and TLR-2 knockout (−/−) mice. In vivo assays were also performed, on which the mice (C57BL/6 and TLR-2−/−) were intraperitoneally infected with S. brasiliensis yeast American Type Culture Collection MYA-4831 and euthanized on days 7, 14 and 28 post infection. The following parameters were then evaluated: fungal burden in spleen, liver, kidney and brain; the production of cytokines TNF-α, IFN-γ, IL-4, IL-2, IL-6 and IL-10.
Results. The in vitro results showed that the absence of TLR-2 resulted in impaired phagocytosis, microbicide mechanisms utilizing the production of nitric oxide, and the cytokine production (TNF-α, IL-6 and IL-10). The in vivo results demonstrated that the absence of TLR-2 during experimental S. brasiliensis infection promoted increased dissemination after 14 and 28 days and suggests a polarized Th17 response in an attempt to control the infection.
Conclusions. TLR-2 signalling appears to be important in the innate immune response against S. brasiliensis.
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The impact of ERAD on recombinant protein secretion in Pichia pastoris (syn Komagataella spp.)
More LessThe yeast Pichia pastoris (syn. Komagataella spp.) is a popular cell factory for recombinant protein production. Yeasts in general provide a good starting point for cell factory engineering. They are intrinsically robust and easy to manipulate and cultivate. However, their secretory pathway is not evolutionarily adapted to high loads of secretory protein. In particular, more complex proteins, like the antibody fragment (Fab) used in this study, overwhelm the folding and secretion capacity. This triggers cellular stress responses, which may cause excessive intracellular degradation. Previous results have shown that, in fact, about 60 % of the newly synthesized Fab is intracellularly degraded. Endoplasmic reticulum-associated protein degradation (ERAD) is one possible intracellular degradation pathway for proteins aimed for secretion. We therefore targeted ERAD for cell factory engineering and investigated the impact on recombinant protein secretion in P. pastoris. Three components of the ERAD-L complex, which is involved in the degradation of luminal proteins, and a protein involved in proteasomal degradation, were successfully disrupted in Fab-secreting P. pastoris. Contrary to expectation, the effect on secretion was marginal. In the course of more detailed investigation of the impact of ERAD, we took a closer look at the intracellular variants of the recombinant protein. This enabled us to further zero in on the issue of intracellular Fab degradation and exclude an overshooting ER quality control. We propose that a major fraction of the Fab is actually degraded before entering the secretory pathway.
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Insights into the candidacidal mechanism of Ctn[15–34] – a carboxyl-terminal, crotalicidin-derived peptide related to cathelicidins
Purpose. Ctn[15–34], a carboxyl-terminal fragment of crotalicidin (a cathelicidin from the venom gland of a South American rattlesnake), has shown antifungal activity against clinical and standard strains of Candida species. The aim of the present work was to investigate the underlying mechanisms of the candidicidal activity of Ctn[15–34].
Methodology. The time-kill profile and drug synergism were evaluated by means of a microdilution assay and multi-parametric flow cytometry. The presumptive interaction of Ctn[15–34] with lipid membranes was estimated in vitro with a lipid-mimic compound, the chromogenic substance 4-nitro-3-(octanoyloxy)benzoic acid (4N3OBA).
Results/Key findings. The absorbance increment (at 425 nm) indicated a concentration- and time-dependent in-solution association between Ctn[15–34] and 4N3OBA. The interaction of Ctn[15-34] with Candida cells was confirmed by flow cytometric measurements with the 5(6)-carboxyfluorescein-labelled peptide (CF-Ctn[15–34]). Analysis of the killing time of Candida exposed to Ctn[15–34] and amphotericin B (AMB) showed that both the peptide and polyene drug reduce the number of c.f.u. but in mechanistically different ways. The Ctn[15–34] peptide alone caused yeast cell membrane disruption, which was confirmed by lactate dehydrogenase leakage and biomarkers of cell death mediated by necrosis.
Conclusion. Overall, Ctn[15–34] displays a synergistic antifungal activity with AMB, an effect that can be further developed into a multi-target therapeutic option with other antimycotics currently in use.
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