The Antarctic yeast Candida sake: Understanding cold metabolism impact on wine

Differences in the management of intracellular redox state between wine yeast species dictate their fermentation performances and metabolite production

The maintenance of the balance between oxidised and reduced redox cofactors is essential for the functioning of many cellular processes in all living organisms. While the electron transport chain plays a key role in maintaining this balance under respiratory conditions, its inactivity in the absence of oxygen poses a challenge that yeasts such as Saccharomyces cerevisiae overcome through the production of various metabolic end-products during alcoholic fermentation. In this study, we investigated the diversity occurring between wine yeast species in their management of redox balance and its consequences on the fermentation performances and the formation of metabolites. To this aim, we quantified the changes in NAD(H) and NADP(H) concentrations and redox status throughout the fermentation of 6 wine yeast species. While the availability of NADP and NADPH remained balanced and stable throughout the process for all the strains, important differences between species were observed in the dynamics of NAD and NADH intracellular pools. A comparative analysis of these data with the fermentation capacity and metabolic profiles of the strains revealed that Saccharomyces cerevisiae, Torulaspora delbrueckii and Lachancea thermotolerans strains were able to reoxidise NADH to NAD throughout the fermentation, mainly by the formation of glycerol. These species exhibited good fermentation capacities. Conversely, Starmerella bacillaris and Metschnikowia pulcherrima species were unable to regenerate NAD as early as one third of sugars were consumed, explaining at least in part their poor growth and fermentation performances. The Kluyveromyces marxianus strain exhibited a specific behaviour, by maintaining similar levels of NAD and NADH throughout the process. This balance between oxidised and reduced redox cofactors ensured the consumption of a large part of sugars by this species, despite a low fermentation rate. In addition, the dynamics of redox cofactors affected the production of by-products by the various strains either directly or indirectly, through the formation of precursors. Major examples are the increased formation of glycerol by S. bacillaris and M. pulcherrima strains, as a way of trying to reoxidise NADH, and the greater capacity to produce acetate and derived metabolites of yeasts capable of maintaining their redox balance. Overall, this study provided new insight into the contribution of the management of redox status to the orientation of yeast metabolism during fermentation. This information should be taken into account when developing strategies for more efficient and effective fermentation.

Antarctic Soil Yeasts with Fermentative Capacity and Potential for the Wine Industry

Low fermentation temperatures are usually employed to obtain high-quality wines. This is especially interesting for white wine production since it prevents the loss of volatile compounds and a browning appearance; however, available fermentative yeasts do not usually tolerate low temperatures. Therefore, an interesting place to find new yeasts with cryotolerance is the Antarctic continent. From soil samples collected in Antarctica, 125 yeasts were isolated, of which 25 exhibited fermentative activity at 10 °C. After a fingerprinting assay, we classified the candidates into nine isotypes and sequenced internal transcribed spacer regions for their identification. These yeasts were identified as part of the Mrakia genus. Sugar and alcohol tolerance tests showed that some of these Antarctic soil yeasts were able to grow up to 9% alcohol, and 25% sugar was reached; however, they exhibited longer latency periods compared to the control Saccharomyces cerevisiae. The optimal growing temperature for the isolated Antarctic yeasts was between 10 °C and 15 °C. A comprehensive analysis of the results obtained showed that the isolates 10M3-1, 4M3-6, and 4B1-35 could be good candidates for fermentation purposes due to their alcohol, sugar tolerance, and growth features. Our results prove that it is possible to isolate fermentative yeasts from Antarctic soil with promising characteristics for their potential use in the wine production industry.

Impact of Candida railenensis during fermentation on the aromatic profile of Vidal blanc icewine

Mixed culture fermentation with non-Saccharomyces yeasts and Saccharomyces cerevisiae as multi-starters has more advantages than spontaneous fermentation, and wine products with distinctive and pleasant aromas can fulfill the diverse demands of consumers. This study was carried out to illuminate the effect of sequential inoculation of indigenous Candida railenensis and S. cerevisiae on alcoholic fermentation behavior and chemical and aromatic characteristics of Vidal blanc icewine. During the mixed culture fermentation, C. railenensis was present in the initial and middle stages but was absent after 14 days. The results of basic chemical parameters showed that the glycerol content in the mixed culture-fermented icewine was higher than that of the pure fermented icewine, but the acetic acid content was the opposite. In terms of volatile aroma compounds, C. railenensis in the mixed culture fermentation reduced some metabolites such as lower alcohols, 1-hexanol, 3-methylthiopropanol, and their unpleasant notes and increased the production of some desired volatile aroma compounds such as benzaldehyde, β-damascenone, 2-furanmethanol, and 5-methyl furfural associated with rose, honey, nut, and caramel characteristics. Furthermore, C. railenensis also changed the sensory performance of icewine by participating in the fermentation of S. cerevisiae. These findings suggest that C. railenensis with positive enological properties has the ability to be used in icewine production, which has never been reported before.

Towards the Development of Microbial Ecotoxicology Testing Using Chlorpyrifos Contaminated Sediments and Marine Yeast Isolates as a Model

Chlorpyrifos (CP), a widely used pesticide, and its metabolite 3,5,6-trichloro-2-pyridinol (3,5,6-TCP), are xenobiotic compounds detected in many biomes, notably in marine sediments, all over the world. These compounds are posing a serious environmental and health problem given their toxicity to wildlife and possible exposure effects to human neurodevelopment. Microorganisms at CP-impacted environments could harbor metabolic capabilities that can be used as indicators of the biological effects of the contaminant and could encode selected functions reactive against contaminants. Those features could be used for microbial ecotoxicology applications by collectively using analytical, enzymatic, microbiological and toxicological techniques in order to assess the biological effects of pollutants and other environmental/climatic stressors in ecosystems. The objective of this study was to assess the variability in the metabolic responses of yeast isolates from CP-contaminated marine sediments as potential biological indicators for microbial ecotoxicology testing. Sediment samples from a South Caribbean tropical shore (Cartagena Bay, Colombia) were collected, and deoxyribonucleic acid (DNA) was recovered from lyophilized aliquots. The DGGE (Denaturing Gradient Gel Electrophoresis) technique targeting fungal Internal Transcribed Spacer (ITS) showed the great diversity of fungal types. Simultaneously, yeast strains were isolated from the freshly collected sediment samples. Physiological characterization including API 20C and antibiosis tests, growth patterns at salt concentrations (2/4/10/25%), temperatures (4/25/37/45 °C), esterase activity assay and resistance tests to CP/TCP toxicity resulted in 10 isolated yeast strains, identified as Candida spp. (6), Cryptococcus spp. (3). and Rhodotorula spp. (1), showing promising characteristics to be used as a test for yeast-based ecotoxicity indicators. The patterns of carbohydrate assimilation, low antibiosis, presence of esterases/lipases, growth in a wide range of temperatures and salt concentrations, and tolerance to minimal inhibitory concentrations of CP and TCP are factors useful for testing environmental samples.

Temporal changes in gastrointestinal fungi and the risk of autoimmunity during early childhood: the TEDDY study

Fungal infections are a major health problem that often begin in the gastrointestinal tract. Gut microbe interactions in early childhood are critical for proper immune responses, yet there is little known about the development of the fungal population from infancy into childhood. Here, as part of the TEDDY (The Environmental Determinants of Diabetes in the Young) study, we examine stool samples of 888 children from 3 to 48 months and find considerable differences between fungi and bacteria. The metagenomic relative abundance of fungi was extremely low but increased while weaning from milk and formula. Overall fungal diversity remained constant over time, in contrast with the increase in bacterial diversity. Fungal profiles had high temporal variation, but there was less variation from month-to-month in an individual than among different children of the same age. Fungal composition varied with geography, diet, and the use of probiotics. Multiple Candida spp. were at higher relative abundance in children than adults, while Malassezia and certain food-associated fungi were lower in children. There were only subtle fungal differences associated with the subset of children that developed islet autoimmunity or type 1 diabetes. Having proper fungal exposures may be crucial for children to establish appropriate responses to fungi and limit the risk of infection: the data here suggests those gastrointestinal exposures are limited and variable.

Yeasts Inhabiting Extreme Environments and Their Biotechnological Applications

Yeasts are microscopic fungi inhabiting all Earth environments, including those inhospitable for most life forms, considered extreme environments. According to their habitats, yeasts could be extremotolerant or extremophiles. Some are polyextremophiles, depending on their growth capacity, tolerance, and survival in the face of their habitat’s physical and chemical constitution. The extreme yeasts are relevant for the industrial production of value-added compounds, such as biofuels, lipids, carotenoids, recombinant proteins, enzymes, among others. This review calls attention to the importance of yeasts inhabiting extreme environments, including metabolic and adaptive aspects to tolerate conditions of cold, heat, water availability, pH, salinity, osmolarity, UV radiation, and metal toxicity, which are relevant for biotechnological applications. We explore the habitats of extreme yeasts, highlighting key species, physiology, adaptations, and molecular identification. Finally, we summarize several findings related to the industrially-important extremophilic yeasts and describe current trends in biotechnological applications that will impact the bioeconomy.

Substrate, temperature, and geographical patterns among nearly 2000 natural yeast isolates

Yeasts have broad importance as industrially and clinically relevant microbes and as powerful models for fundamental research, but we are only beginning to understand the roles yeasts play in natural ecosystems. Yeast ecology is often more difficult to study compared to other, more abundant microbes, but growing collections of natural yeast isolates are beginning to shed light on fundamental ecological questions. Here, we used environmental sampling and isolation to assemble a dataset of 1962 isolates collected from throughout the contiguous United States of America (USA) and Alaska, which were then used to uncover geographic patterns, along with substrate and temperature associations among yeast taxa. We found some taxa, including the common yeasts Torulaspora delbrueckii and Saccharomyces paradoxus, to be repeatedly isolated from multiple sampled regions of the USA, and we classify these as broadly distributed cosmopolitan yeasts. A number of yeast taxon-substrate associations were identified, some of which were novel and some of which support previously reported associations. Further, we found a strong effect of isolation temperature on the phyla of yeasts recovered, as well as for many species. We speculate that substrate and isolation temperature associations reflect the ecological diversity of and niche partitioning by yeast taxa.

A review of fruit juice authenticity assessments: Targeted and untargeted analyses

Fruit juices are becoming more and more popular in the whole world. However, the increasing fruit juice fraud cases are undermining the healthy development of fruit juice industry. Fruit juice authenticity represents an important food quality and safety parameter. Many techniques have been applied in fruit juices authenticity assessment. The purpose of this review is to provide a research overview of the targeted and untargeted analyses of fruit authentication, and a method selection guide for fruit juice authenticity assessment. Targeted markers, such as stable isotopes, phenolics, carbohydrates, organic acids, volatile components, DNAs, amino acids and proteins, as well as carotenoids, will be discussed. And untargeted techniques, including liquid/gas chromatography-mass spectrometer, nuclear magnetic resonance, infrared spectroscopy, inductively-coupled plasma-mass spectrometry/optical emission spectrometer, fluorescence spectra, electronic sensors and others, will be reviewed. The emerging untargeted for novel targeted marker analysis will be also summarized.

The Effect of Non-Saccharomyces and Saccharomyces Non-Cerevisiae Yeasts on Ethanol and Glycerol Levels in Wine

Non-Saccharomyces and Saccharomyces non-cerevisiae studies have increased in recent years due to an interest in uninoculated fermentations, consumer preferences, wine technology, and the effect of climate change on the chemical composition of grapes, juice, and wine. The use of these yeasts to reduce alcohol levels in wines has garnered the attention of researchers and winemakers alike. This review critically analyses recent studies concerning the impact of non-Saccharomyces and Saccharomyces non-cerevisiae on two important parameters in wine: ethanol and glycerol. The influence they have in sequential, co-fermentations, and solo fermentations on ethanol and glycerol content is examined. This review highlights the need for further studies concerning inoculum rates, aeration techniques (amount and flow rate), and the length of time before Saccharomyces cerevisiae sequential inoculation occurs. Challenges include the application of such sequential inoculations in commercial wineries during harvest time.

Cryopreservation and the Freeze-Thaw Stress Response in Yeast

The ability of yeast to survive freezing and thawing is most frequently considered in the context of cryopreservation, a practical step in both industrial and research applications of these organisms. However, it also relates to an evolved ability to withstand freeze-thaw stress that is integrated with a larger network of survival responses. These responses vary between different strains and species of yeast according to the environments to which they are adapted, and the basis of this adaptation appears to be both conditioned and genetic in origin. This review article briefly touches upon common yeast cryopreservation methods and describes in detail what is known about the biochemical and genetic determinants of cell viability following freeze-thaw stress. While we focus on the budding yeast Saccharomyces cerevisiae, in which the freeze-thaw stress response is best understood, we also highlight the emerging diversity of yeast freeze-thaw responses as a manifestation of biodiversity among these organisms.

Impact of fermentation conditions on the diversity of white colony-forming yeast and analysis of metabolite changes by white colony-forming yeast in kimchi

The presence of white colony-forming yeast (WCFY) on kimchi surfaces indicates a reduction in kimchi quality. This study aimed to investigate the effect of different fermentation temperatures (4, 10, and 20 °C) and packaging conditions (open or closed) on WCFY diversity, and the changes of metabolite by the difference of WCFY diversity. Community analysis using high-throughput DNA sequencing revealed that Kazachstania servazzii and K. barnettii were most prevalent in kimchi fermented under closed packaging condition at 4, 10, and 20 °C. In open packaging condition, four species of Candida sake, K. servazzii, K. barnettii, and Tausonia pullulans were the predominant yeast species at 4 °C, and four species of C. sake, K. servazzii, K. barnettii, and Debaryomyces hancenii were predominantly detected at 10 °C. The diversity of the WCFY community was higher under the open rather than the closed packaging condition. However, at all fermentation temperatures, non-volatile metabolite production by the different WCFY communities did not significantly differ between open and closed packaging conditions, whereas glycerol levels in kimchi samples harboring WCFY increased relative to the control (0 day). These results indicate that fermentation temperature and air exposure can alter WCFY diversity on kimchi surface, however, non-volatile metabolite profiles in kimchi soup are not significantly affected by the difference of WCFY diversity caused by packaging conditions. This study furthers the current understanding of the growth of undesirable WCFY in kimchi.

A Rapid Method for Selecting Non-Saccharomyces Strains with a Low Ethanol Yield

The alcohol content in wine has increased due to external factors in recent decades. In recent reports, some non-Saccharomyces yeast species have been confirmed to reduce ethanol during the alcoholic fermentation process. Thus, an efficient screening of non-Saccharomyces yeasts with low ethanol yield is required due to the broad diversity of these yeasts. In this study, we proposed a rapid method for selecting strains with a low ethanol yield from forty-five non-Saccharomyces yeasts belonging to eighteen species. Single fermentations were carried out for this rapid selection. Then, sequential fermentations in synthetic and natural must were conducted with the selected strains to confirm their capacity to reduce ethanol compared with that of Saccharomyces cerevisiae. The results showed that ten non-Saccharomyces strains were able to reduce the ethanol content, namely, Hanseniaspora uvarum (2), Issatchenkia terricola (1), Metschnikowia pulcherrima (2), Lachancea thermotolerans (1), Saccharomycodes ludwigii (1), Torulaspora delbrueckii (2), and Zygosaccharomyces bailii (1). Compared with S. cerevisiae, the ethanol reduction of the selected strains ranged from 0.29 to 1.39% (v/v). Sequential inoculations of M. pulcherrima (Mp51 and Mp FA) and S. cerevisiae reduced the highest concentration of ethanol by 1.17 to 1.39% (v/v) in synthetic or natural must. Second, sequential fermentations with Z. bailii (Zb43) and T. delbrueckii (Td Pt) performed in natural must yielded ethanol reductions of 1.02 and 0.84% (v/v), respectively.

Metabolites analysis for cold-resistant yeast (Wickerhamomyces anomalus) strains own antioxidant activity on cold stored fish mince

The effect of eight cold-resistant yeast strains (J3, J7, J8, J9, J12, J15, J18, and J25) of Wickerhamomyces anomalus on the lipid oxidation of cold stored fish mince (4 °C) were investigated. And the metabolites of these yeast were determined with gas chromatography-mass spectrometry. These strains could effectively inhibit the increase of hydroperoxides value (p < 0.05), and the inhibiting rate was positively correlated with the content of isolongifolene, xylitol, turanose, thymol-glucoside, and uridine. Especially, the J3, J7, J8, J9, J12, and J18 could eliminate a large part of thiobarbituric acid reactive substances (TBARS) (p < 0.05), the eliminating rate was proportionate to the aldehyde dehydrogenase activity. Several bacteriostatic metabolites were detected: thymol-glucoside, 2-phenylethanol, cedro, and 2,4-bis (1,1-dimethylethyl) phenol. In addition, W. anomalus produced many metabolites with fruit and floral notes. In conclusion, cold-resistant W. anomalus strains own antioxidant activity were potential new bio-preservatives in the cold storage of muscle products.

Microbiological strategies to produce beer and wine with reduced ethanol concentration

Changes in consumer preferences, government policies and environmental conditions have driven research efforts towards producing alcoholic beverages with reduced alcohol content, namely wine and beer. While the strategies available to accomplish this goal vary for wine and beer, a common approach relies on the use of yeast strains which are less efficient at producing ethanol. Here we discuss current research on the isolation and/or generation of yeast strains able to produce beer or wine with reduced ethanol concentration. Particular consideration is given to the impact of 'low-ethanol' yeasts on volatile composition and sensory profile of beer and wine.

Glycerol metabolism genes in Aureobasidium pullulans and Aureobasidium subglaciale

Intracellular glycerol accumulation is one of the main fungal adaptations to osmotic and also cold stress. We investigated the management of glycerol metabolism in polyextremotolerant black yeasts Aureobasidium pullulans and Aureobasidium subglaciale. We show that increased salinity (5 % and 10 %; w/v), but not cold (10 °C) trigger intracellular glycerol accumulation. The transcriptional response of the genes involved in glycerol synthesis, degradation and import, to increased salinity, low temperature or a combination of both was analysed with real-time PCR. Each of the two species contains an NAD⁺-dependent glycerol-3-phosphate dehydrogenase, a glycerol-3-phosphate phosphatase, a mitochondrial glycerol-3-phosphate dehydrogenase, two copies of a glycerol kinase, and more than ten copies of major facilitator superfamily transporters similar to glycerol proton symporters. Similarly to glycerol accumulation itself, transcriptional response to hypersaline stress was larger compared to low temperature stress and was more consistent in A. pullulans compared to A. subglaciale, reflecting the different stress tolerance and ecological strategy of each species.