Dead Yeast Research Articles

Sustainable Exploitation of Wine Lees as Yeast Extract Supplement for Application in Food Industry and Its Effect on the Growth and Fermentative Ability of Lactiplantibacillus plantarum and Saccharomyces cerevisiae

Wine lees, the residue left behind after racking or bottling of wine, are predominantly composed of dead yeast cells, ethanol, phenolic compounds, and tartrates. Yeast extract (i.e., commercial yeast extract), a highly nutritious powder derived from commercially cultivated yeast biomass, is commonly used in nutrient media as a nitrogen source. In the context of by-product valorization, wine lees could potentially be used to produce a substitute for commercial yeast extract (CYE). In our study we investigated the growth and fermentative ability of two major winemaking microorganisms, Lactiplantibacillus plantarum and Saccharomyces cerevisiae, in culture media containing a wine lees yeast extract (WLYE) and a CYE. The effects of yeast extract type, concentration, and initial cell concentration (y0) on key kinetic parameters—maximum specific growth rate (μmax), lag phase duration (λ), and maximum cell concentration (ymax)—were evaluated. For L. plantarum, the results showed that using a WLYE led to similar kinetic parameters to those obtained with a CYE, with λ being unaffected by y0 in samples containing a WLYE. For S. cerevisiae, simultaneous addition of both yeast extracts led to increased μmax values (up to 0.136 h−1) compared to individually added yeast extracts, although this negatively affected λ and ymax. Current research on wine lees is mainly focused on using them as a substrate to produce valuable metabolites through fermentation, overlooking the potential industrial applications of the nutrient-rich autolysate. The findings of this study appear promising for the holistic valorization of wine lees, contributing towards the concepts of sustainability and circular economy.

Valorization of the solid fraction of wine lees through optimized accelerated autolysis: Effect of temperature, pH and solid concentration on free-amino acid concentration

Winemaking, as an agro-industrial process, generates substantial amounts of by-products, notably grape pomace and wine lees. The latter constitutes the residue left behind during the racking or bottling of wine, consisting mainly of dead yeast cells, ethanol, phenolic compounds, tartrates, and other compounds. Within the framework of by-products’ valorization, the rich content of dead yeast cells in wine lees render them conducive to the production of a yeast extract substitute through autolysis. In the present study, the effect of pretreatment, temperature, pH, and solid concentration on the efficiency of white wine lees autolysis was investigated. Moreover, the effect of enzyme addition and dynamic thermal protocols were investigated. Efficiency assessment was based on the increase of free α-amino nitrogen (FAN) found in the autolysate. The finding revealed a significant increase of FAN in all cases, with treated and untreated white wine lees reaching a maximum increase of 477% and 834%, respectively. Furthermore, the amino acid profile of autolysates was significantly affected by the autolysis temperature. These results hold promise for the comprehensive, holistic valorization of wine lees, suggesting their potential use as a nutrient source for microorganisms, such as wine yeast, or even as a grape must nitrogen modulator. Consequently, this by-product can be integrated back into the same industrial process from which it originates, namely winemaking. This not only aligns with the principles of circular economy but also underscores the potential for sustainable development within wineries.

Safety and efficacy indicators of guarana and Brazil nut extract carried in nanoparticles of coenzyme Q10: Evidence from human blood cells and red earthworm experimental model

This study characterized a nanosupplement based on coenzyme Q10 containing guarana (Paullinia cupana) and Brazil nuts oil (Bertholetia excelsa) (G-Nut). Determined cytotoxic and oxi-immunomodulatory effects on human peripheral blood mononuclear cells (PBMCs) and its effect on mortality of red Californian earthworms (Eisenia fetida) and on the immune efficiency of its coelomocytes immune by in vitro exposure to yeast dead microorganism. The cytotoxic and immunomodulatory effects of G-Nut and the GN-Free extract (0.25–3 mg/mL) were determined in PBMC cultures. Apoptotic, oxidative, and inflammatory markers were determined using biochemical, immunological, and molecular protocols. The effects of G-Nut and GN-Free extracts on mortality and immune efficiency were investigated in earthworms. G-Nut and GN-Free did not induce cytotoxic events in PBMCs, triggering the decrease in apoptotic (caspases 3 and 8) gene expression, lipid and protein oxidation levels, or pro-inflammatory cytokine levels. G-Nut and GN-Free did not trigger earthworm mortality and improved coelomocyte immune efficiency by increasing Eisenia neutrophil extracellular DNA traps and brown body formation when exposed to dead yeasts. The G-Nut nanoformulation is safe and can be used as a new form of food supplement by oral or transdermal delivery.

Dielectrophoretic cell sorting with high velocity enabled by two-layer sidewall microelectrodes extending along the entire channel

Dielectrophoresis has been widely applied in microfluidic cell separation, and it enables label-free and size-independent cell sorting based on their dielectric fingerprints which is prerequisite for downstream biomedical analysis. The linear flow velocity and cross-sectional area are the two key factors proportional to the flow rate and thus directly related to the sample processing throughput. Aiming at higher flow rate, the state-of-art techniques mostly focus on the cross-sectional area, either by using wide chamber with angled electrode digits or 3D volumetric electrodes with expanded channel depth. On the other hand, the velocity is always carefully limited because cells have very squeezed time to interact with the DEP force that drives them to migrate, and the flow drag induced by high velocity potentially poses adverse effect against the DEP-driven cell migration. In this paper, we present DEP-activated cell sorting at high-velocity being 1–2 orders of magnitude higher than the existing DEP separators, which is enabled by easily-fabricated two-layer 3D sidewall electrodes extending along the entire flow channel. Such electrodes project DEP force fully decoupled from the flow drag, and acting on cells continuously, allowing sufficient time for cell migration. The two-layer design leads to cell migration across a shorter distance between the upper and lower layers, with a unique bridge adaptor evolved at the downstream for the collection of the cells vertically separated. The DEP device achieves separation of live and dead yeast cells at high velocity up to 78.3 mm/s, more than a full order of magnitude higher compared to any reported DEP platforms. This velocity corresponds to a competitive flow rate of 3.1 mL/h given the fairly small cross-sectional area, where the averaged collection rate is over 95 %. For the separation between the live and dead Hela cells, our device enables a high velocity up to 50.5 mm/s with an averaged collection rate of ∼85 %. A high throughput of 1.79 × 1 0^(5) cells/min for the live and dead Hela cell separation has been achieved with 89.7 % collection for live cells and a velocity of 30.3 mm/s.

Portable dielectrophoresis for biology: ADEPT facilitates cell trapping, separation, and interactions

Dielectrophoresis is a powerful and well-established technique that allows label-free, non-invasive manipulation of cells and particles by leveraging their electrical properties. The practical implementation of the associated electronics and user interface in a biology laboratory, however, requires an engineering background, thus hindering the broader adoption of the technique. In order to address these challenges and to bridge the gap between biologists and the engineering skills required for the implementation of DEP platforms, we report here a custom-built, compact, universal electronic platform termed ADEPT (adaptable dielectrophoresis embedded platform tool) for use with a simple microfluidic chip containing six microelectrodes. The versatility of the open-source platform is ensured by a custom-developed graphical user interface that permits simple reconfiguration of the control signals to address a wide-range of specific applications: (i) precision positioning of the single bacterium/cell/particle in the micrometer range; (ii) viability-based separation by achieving a 94% efficiency in separating live and dead yeast; (iii) phenotype-based separation by achieving a 96% efficiency in separating yeast and Bacillus subtilis; (iv) cell–cell interactions by steering a phagocytosis process where a granulocyte engulfs E. coli RGB-S bacterium. Together, the set of experiments and the platform form a complete basis for a wide range of possible applications addressing various biological questions exploiting the plug-and-play design and the intuitive GUI of ADEPT.

Acute Bisphenol-A exposure triggers superoxide-nitric oxide imbalance and immunocompetence impairment of Eisenia fetida earthworm

Bisphenol-A (BPA) is an endocrine-disrupting molecule associated with the risk of several non-transmissible chronic diseases. We postulated that BPA triggers oxidative alterations, altering immunocompetence and contributing to physiological dysfunction. To evaluate the effects of BPA on the oxidative and immune system, Californian earthworms were reared in a culture medium containing different BPA concentrations for 24 and 72 h. Coelomocytes were used to evaluate the effects of BPA on oxidative markers, cellular proliferation, and apoptosis, and immunocompetence effects were investigated by yeast-exposure assay and the modulation of genes related to immune response. Low BPA concentrations induced coelomocyte proliferation, imbalanced superoxide/NO levels, higher micronucleus frequency, and apoptosis. BPA also induced Amp1 gene overexpression and a low efficiency of dead yeast capture. The association between DNA damage and changes in innate immune metabolism could be related to the action of BPA, which is associated with the risk of physiological disturbances and non-transmissible chronic diseases.

Power loss model of electromagnetic waves propagation in cell solutions by GHz electrical impedance spectroscopy

The propagation of GHz electromagnetic (EM) waves across cells in cell solutions has been analytically modeled and numerically calculated in order to elucidate the power loss in the boundary between dispersed medium and cell by establishing a theoretical model. Living and dead yeast cells are chosen as objects because of the simple cell structure and ease of observation under optical microscope. Through the model, the average power density of the incident wave S avi , reflected wave S avr , transmitted wave S avt , and ratio of the power loss ψ are calculated and compared to analyze the power loss of EM waves inside living and dead yeast cells by considering the impacts of frequency of EM wave, cell viability, concentration, and component structures of the cell. Results demonstrate decreased S avi, S avr , and S avt with rising frequency, especially noticeable below 100 MHz due to enhanced absorption from cell components. EM waves in living yeast cell solutions exhibit faster attenuation and stronger reflection compared to dead yeast cells, attributed to intact organelles and membranes intensifying absorption and scattering. The increasing cells concentration further attenuates EM waves. This work elucidates propagation and power loss of EM waves in cell solutions and provides an effective computational approach to optimize EM wave based biomedical applications.

Fabrication and properties of temperature-responsive imprinted sensors based on fluorescently labeled yeast cells via MVL ATRP.

Temperature-responsive yeast cell-imprinted sensors (CIPs/AuNPs/Ti3C2Tx/AuNPs/Au) were prepared based on fluorescein isothiocyanate labeled yeast cells (FITC-yeast) via metal-free visible-light-induced atom transfer radical polymerization (MVL ATRP). Here, N-isopropyl acrylamide (NIPAM) was used as a temperature-responsive functional monomer, α-methacrylic acid (MAA) was chosen as an auxiliary functional monomer, N,N'-methylene bisacrylamide (MBA) was used as a cross-linker, and FITC-yeast was selected as both a template and photocatalyst. Under the optimal conditions, the detection range of the yeast cell-imprinted sensor toward yeast cells was 1.0 × 102 to 1.0 × 109 cells per mL, and the detection limit was 11 cells per mL (S/N = 3), with a linear equation of ΔI (μA) = 8.44 log[C (cells per mL)] + 7.62 (R2 = 0.993). The sensor showed good selective recognition in the presence of interfering substances such as autolyzed yeast cells (AY), dead yeast cells (DY), human mammary epithelial cells (MCF-10A), human breast cancer cells (MCF-7) and Escherichia coli (EC). The sensor also had good consistency and reproducibility. Finally, spiked recovery experiments were performed to investigate the recognition of yeast cells in the actual sample using the yeast cell-imprinted sensor. The spiked recoveries were all in the range of 98.5-108.0%, and the RSD values were all less than 4%, indicating that the sensor had good application prospects.

Sur lies élevage practice to modulate the features of red wines from calcareous soils with different textures.

In Sicilian calcareous soils, red wines often display unripeness and bitterness features. To enhance wine quality, we employed the 'sur lies élevage' technique, involving prolonged contact of dead yeast cells with the wine to favor the extraction of yeast cellular components through cell lysis. The 7 month treatment utilized two types of Chardonnay lies: fresh and previously matured. To overcome challenges in retrieving lies from red winemaking, we have recovered the lies from a white winemaking. Additionally, the lies underwent a preliminary passage on a red wine to minimize color adsorption on yeast cell walls. The sur lies treatment effectively reduced astringency, bitterness, and brown pigment in wines, with partial removal of red color. It successfully eliminated quercetin aglycone and induced remarkable changes in the aromatic profile, showing increased ethyl esters and relative fatty acids. Sensory evaluations revealed sur lies-treated wines had fruitier and more complex characteristics compared to untreated wines. Matured lies had a greater impact on enhancing fruitiness than fresh lies. The treatments mitigated the unripeness and bitterness of studied wines. Sur lies treatment improved the aromatic profile, leading to fruitier and more complex notes, enhancing overall sensory quality. Matured lies showed greater efficacy in elevating fruitiness than fresh lies. These findings highlight the value of the sur lies technique in enhancing the quality and sensory attributes of Nero d'Avola and Syrah wines from Sicilian calcareous soils. © 2023 Society of Chemical Industry.

Antimicrobial function of yeast against pathogenic and spoilage microorganisms via either antagonism or encapsulation: A review.

Contaminations of pathogenic and spoilage microbes on foods are threatening food safety and quality, highlighting the importance of developing antimicrobial agents. According to different working mechanisms, the antimicrobial activities of yeast-based agents were summarized from two aspects: antagonism and encapsulation. Antagonistic yeasts are usually applied as biocontrol agents for the preservation of fruits and vegetables via inactivating spoilage microbes, usually phytopathogens. This review systematically summarized various species of antagonistic yeasts, potential combinations to improve the antimicrobial efficiency, and the antagonistic mechanisms. The wide applications of the antagonistic yeasts are significantly limited by undesirable antimicrobial efficiency, poor environmental resistance, and a narrow antimicrobial spectrum. Another strategy for achieving effective antimicrobial activity is to encapsulate various chemical antimicrobial agents into a yeast-based carrier that has been previously inactivated. This is accomplished by immersing the dead yeast cells with porous structure in an antimicrobial suspension and applying high vacuum pressure to allow the agents to diffuse inside the yeast cells. Typical antimicrobial agents encapsulated in the yeast carriers have been reviewed, including chlorine-based biocides, antimicrobial essential oils, and photosensitizers. Benefiting from the existence of the inactive yeast carrier, the antimicrobial efficiencies and functional durability of the encapsulated antimicrobial agents, such as chlorine-based agents, essential oils, and photosensitizers, are significantly improved compared with the unencapsulated ones.

Safe, rapid, and easy electro-orientation-based viability assay using a disposable insulating envelope within non-spherical yeast cells

Rapid and easy assays for fungal viability and susceptibility to antifungal drugs are important for controlling fungal infections and diseases. We developed an improved electro-orientation (EO) viability assay, in which opposite EO directions for living and dead non-spherical yeast cells in alternating current (AC) electric fields are observed under a light microscope. An envelope-type cell injection device was constructed with two 5-μm ultrathin insulating polyimide films to avoid direct cell–electrode contact via cross-contamination. The envelope, within a 1 µL cell sample, was sandwiched between a pair of indium-tin-oxide plate electrodes. After use, the disposable envelope within the cells could be peeled off and discarded, providing reusability of the electrodes while preventing biohazards. Furthermore, cell samples were prepared within 10 s by simply diluting the cell culture medium with distilled water to reduce the extracellular conductivity to 3 mS/m, without centrifugation. This resulted in almost no time lag between sampling and assessment. The antifungal efficacy of nystatin was evaluated by applying an AC voltage of 7 V at 10 MHz, for 5 s, using the envelope device. The improved EO method enabled safe, rapid, and easy viability assays with a single-use envelope and simplified sample preparation.

Effect of ageing on lees on the quality of white and rosé wines from Iași vineyard

Ageing of wines on lees (autolysis) involves keeping wines in contact with dead yeast cells for several months/years to intensify the transfer of compounds between yeast cells and wine. During yeast autolysis, release of different compounds has been shown to have a positive influence on organoleptic characteristics of wine as these compounds, including lipids, mannoproteins, peptides, proteins, amino acids, and glucans, are breakdown products of yeasts and can impact on volatile profile of wine. The aim of this study was to evaluate the quality of white and rosé wines aged in contact with lees for 2 months, using 12 commercial maturation products. The studied wines were produced in Iasi vineyard, vintage 2020, from Sauvignon blanc and Busuioacă de Bohotin grapes variety. Thus, 26 samples were obtained (V1 SB-V13 SB; V1 BB – V13 BB). The effect of ageing on lees was assessed by analysing some main aroma compounds, performing an organoleptic analysis and quantifying color changes (CIEL ab parameters). The first impression that the consumer receives from wine is color and to some extent it can influence the taste. In terms of color parameters, an increase in color intensity was evident for all samples after the lees ageing period. Sensorial analysis coupled with statistical analysis tests showed a definite correlation between the maturation products used and their composition vs. certain sensorial indices. The treated wines boasted a smoother sensorial profile, with enhancement of mouth feel and persistence (V2, 3, 11 SB and V2, 3, 11 BB).

A Self-Powered Dielectrophoretic Microparticle Manipulation Platform Based on a Triboelectric Nanogenerator.

Lab-on-a-chip systems aim to integrate laboratory operations on a miniaturized device with broad application prospects in the field of point-of-care testing. However, bulky peripheral power resources, such as high-voltage supplies, function generators, and amplifiers, hamper the commercialization of the system. In this work, a portable, self-powered microparticle manipulation platform based on triboelectrically driven dielectrophoresis (DEP) is reported. A rotary freestanding triboelectric nanogenerator (RF-TENG) and rectifier/filter circuit supply a high-voltage direct-current signal to form a non-uniform electric field within the microchannel, realizing controllable actuation of the microparticles through DEP. The operating mechanism of this platform and the control performance of the moving particles are systematically studied and analyzed. Randomly distributed particles converge in a row after passing through the serpentine channel and various particles are separated owing to the different DEP forces. Ultimately, the high-efficiency separation of live and dead yeast cells is achieved using this platform. RF-TENG as the power source for lab-on-a-chip exhibits better safety and portability than traditional high-voltage power sources. This study presents a promising solution for the commercialization of lab-on-a-chip.

Safety evaluation of the use of the non-genetically modified Hamamotoa singularis strain YIT 10047 as a source of β-galactosidase.

This assessment addresses the enzyme β-galactosidase which is not separated from the yeast cells used for its production. The β-galactosidase (β-D-galactoside galactohydrolase, EC 3.2.1.23) is produced with the non-genetically modified Hamamotoa singularis (formerly Sporobolomyces singularis) strain YIT 10047 by Yakult Pharmaceutical Industry Co., Ltd. The yeast cell suspension contains both live and dead yeast cells. It is intended to be used in the production of galacto-oligosaccharides (GOS). The final GOS products are free of viable cells of the H. singularis. Dietary exposure to the food enzyme total organic solids (TOS) was estimated to be up to 0.683mg TOS/kg body weight (bw) per day in European populations. Genotoxicity tests of the cell suspension did not indicate a safety concern. The systemic toxicity was assessed by means of a repeated dose 90-day oral toxicity study in rats. The Panelidentified a no observed adverse effect level of 296.25mg TOS/kg bw per day, the highest dose tested. This results in a margin of exposure above 434. A search for the similarity of the amino acid sequence of the β-galactosidase to known allergens was made and no matches were found. The Panelconsidered that, under the intended conditions of use, the risk of allergic reactions by dietary exposure cannot be excluded, but the likelihood for this to occur is low. Based on the data provided, the Panelconcluded that this yeast suspension used as a source of β-galactosidase does not give rise to safety concerns under the intended conditions of use.

Alternating-current nonlinear electrokinetics in microfluidic insulator-decorated bipolar electrochemistry

We proposed herein a unique method of insulator-decorated bipolar electrochemistry (IDBE), for realizing large-scale separation of bioparticles in microchannels driven by AC dielectrophoresis (DEP). In IDBE, a pair of planar driving electrodes is placed at the bottom of channel sidewalls, between which an array of the rectangular floating electrode (FE) strips without external Ohmic contact are evenly spaced along transversal direction, and a series of insulating dielectric blocks are periodically deposited above all the inter-electrode gaps and in full contact with the channel bottom surface. By creating local field maximum and minimum at multiple sites, IDBE extends well the actuating range of DEP force field from the immediate vicinity of electrode tips in traditional bipolar electrochemistry to current fluid bulk. Considering DEP force plays the dominant role around 1 MHz, we utilize Lagrange particle tracing algorithm to calculate motion trajectories of incoming samples for testing the feasibility of microchip in continuous separation of live and dead yeast cells. By applying suitable voltage parameters, highly efficient DEP sorting is theoretically achievable under a moderate inlet flow rate, where most of the viable yeasts are trapped by positive-DEP to sharp dielectric edges, while all the incoming nonviable yeasts are repelled by negative-DEP to the top surface of both FE and insulating block to form multiple thin beams co-flowing into the channel outlet. The microfluidic device exploiting insulators on bipolar FE effectively expands the actuating range of nonlinear electrodynamics and provides invaluable guidelines for developing flexible electrokinetic frameworks in modern microfluidic systems.

Label-free viability assay using in-line holographic video microscopy

Total holographic characterization (THC) is presented here as an efficient, automated, label-free method of accurately identifying cell viability. THC is a single-particle characterization technology that determines the size and index of refraction of individual particles using the Lorenz–Mie theory of light scattering. Although assessment of cell viability is a challenge in many applications, including biologics manufacturing, traditional approaches often include unreliable labeling with dyes and/or time consuming methods of manually counting cells. In this work we measured the viability of Saccharomyces cerevisiae yeast in the presence of various concentrations of isopropanol as a function of time. All THC measurements were performed in the native environment of the sample with no dilution or addition of labels. Holographic measurements were made with an in-line holographic microscope using a 40times objective lens with plane wave illumination. We compared our results with THC to manual counting of living and dead cells as distinguished with trypan blue dye. Our findings demonstrate that THC can effectively distinguish living and dead yeast cells by the index of refraction of individual cells.

Silver Nanoparticles: A Promising Antifungal Agent against the Growth and Biofilm Formation of the Emergent Candida auris.

Candida auris is a globally-emerging pathogen that is correlated to nosocomial infections and high mortality rates, causing major outbreaks in hospitals and serious public health concerns worldwide. This study investigated the antifungal activity of silver nanoparticles (AgNPs) on clinical isolates of C. auris. A total of eight clinical isolates were collected from blood, urine, ear swab, and groin. C. auris was confirmed by MALDI-TOF MS, and gene sequencing. All isolates confirmed as C. auris were subjected to antimicrobial agents, including amphotericin B, fluconazole, caspofungin, voriconazole, micafungin, and flucytosine. A serial dilution of a silver nanoparticles solution was prepared to test antifungal susceptibility testing under planktonic conditions. Moreover, an antibiofilm activity assay was determined using a colony-forming assay and a cell viability assay by a live–dead yeast kit. Significant antifungal and antibiofilm activity of AgNPs was detected against all isolates; MIC was <6.25 μg/mL, the range of MFC was from 6.25 to 12.5 μg/mL for all isolates, and the highest value of IC50 was 3.2 μg/mL. Silver nanomaterials could represent a possible antimicrobial agent to prevent outbreaks caused by C. auris infections.

Synthesis of silver nanoclusters in colloidal scaffold for biolabeling and antimicrobial applications

A robust method to prepare silver nanoclusters (AgNCs) inside a methacrylic acid-ethyl acrylate (MAA-EA) nanogel is proposed, where AgNCs were produced within the nanogel scaffold via UV-photoreduction. The impact of UV irradiation time on the formation of AgNCs and their application in biolabeling and antimicrobial properties were examined. The AgNCs formation is described by two stages; (1) Agn (n = 2–8) nanoclusters formation between 0 and 25 min, and (2) larger silver nanoparticles (AgNPs) formed via aggregation inside the nanogel. The antimicrobial performance depended on the size and concentration of silver ions (Ag+). A maximum inhibitory concentration (MIC) of 1.1 ppm was observed for antimicrobial test with yeast, and a MIC of 11 and 22 ppm was recorded for Escherichia. coli and Staphylococcus aureus respectively. Combining with the green illumination property of AgNCs (emitted at 525 nm) with dead yeast, it could be used for biolabeling. By tuning the size through photoirradiation, the nanogel templated AgNCs is a promising candidate for antimicrobial and biolabeling applications.

Boundary Reflection Derivation Method for Intracellular Structure Change Based on GHz Electrical Impedance Spectroscopy

Boundary reflection derivation method has been proposed in order to clarify intracellular structure change among the cell wall, membrane, and cytoplasm in the frequency range from 1 MHz to 3 GHz. This method is composed of three steps, which are 1) dielectric properties extraction of dispersed medium $\varepsilon _{\mathrm {dis}}^{\ast }$ and yeast cells $\varepsilon _{\mathrm {cell}}^{\ast }$ ; 2) dielectric properties fitting of cell wall $\varepsilon _{\mathrm {wall}}^{\ast }$ , membrane $\varepsilon _{\mathrm {mem}}^{\ast }$ , cytoplasm $\varepsilon _{\mathrm {cyto}}^{\ast }$ , and intracellular components $\varepsilon _{\mathrm {IC}}^{\ast }$ by a multishelled sphere model; and 3) reflection coefficients calculation at boundaries between cell wall and membrane $\Gamma _{\text {wm}}^{\ast }$ , and between membrane and cytoplasm $\Gamma _{\text {mc}}^{\ast }$ . With this method, $\Gamma _{\text {wm}}^{\ast }$ and $\Gamma _{\text {mc}}^{\ast }$ in living (LC) and dead (DC) yeast cell solutions with various volume concentrations are calculated from experimental impedances. $\Gamma _{\text {wm}}^{\ast \text {DC}}$ shows a difference as compared with $\Gamma _{\text {wm}}^{\ast \text {LC}}$ in GHz range. $\Gamma _{\text {wm}}^{\ast \text {LC}}$ and $\Gamma _{\text {mc}}^{\ast \text {LC}}$ illustrate electromagnetic waves penetrate yeast cell membrane and cytoplasm in GHz range nevertheless they are reflected in MHz range.

Chronic Diseases Associated with Malassezia Yeast.

Malassezia are a lipid-dependent basidiomycetous yeast of the normal skin microbiome, although Malassezia DNA has been recently detected in other body sites and has been associated with certain chronic human diseases. This new perspective raises many questions. Are these yeasts truly present in the investigated body site or were they contaminated by other body sites, adjacent or not? Does this DNA contamination come from living or dead yeast? If these yeasts are alive, do they belong to the resident mycobiota or are they transient colonizers which are not permanently established within these niches? Finally, are these yeasts associated with certain chronic diseases or not? In an attempt to shed light on this knowledge gap, we critically reviewed the 31 published studies focusing on the association of Malassezia spp. with chronic human diseases, including psoriasis, atopic dermatitis (AD), chronic rhinosinusitis (CRS), asthma, cystic fibrosis (CF), HIV infection, inflammatory bowel disease (IBD), colorectal cancer (CRC), and neurodegenerative diseases.