Identification of yeast species from orange fruit and juice by RFLP and sequence analysis of the 5.8S rRNA gene and the two internal transcribed spacers

Hanensula anomala isolated from the Berkeley Pit, Butte, MT, is a metal-specific extremophile

A yeast-like extremophile organism, Hansenula anomala, has been isolated from the superfund site the Berkeley Pit Lake in Butte, Montana. Studies demonstrate H. anomala growth in some of the known Berkeley Pit Lake solutes. Microbial growth dynamics under controlled conditions were compared of H. anomala for multiple metal concentrations. Each solute/metal was tested separately at previously reported concentrations on the geochemistry of the Berkeley Pit lake in the first 0.2 m in spring (pH 2.5). H. anomala grew well with sulfur (S), MgSO4, CaSO4, potassium chloride (KCl), and NaSO4 and was inhibited with FeSO4, MnSO4, CuSO4, AlSO4, or ZnSO4. With the addition of elemental S, growth was observed for FeSO4 indicating minimal growth rescue. PCR amplification of genomic DNA from the organism using known ribosomal primers indicates the strain to be ATCC8168 (CBS 5759). From this data, it can be concluded that H. anomala ATCC8168 from the Berkeley Pit is an extremophile that exhibits metal-specific growth.IMPORTANCELaboratory growth studies of a strain of Hansenula anomala from the Berkeley Pit have found the organism to be metal specific indicating some unique metabolism possibilities. These studies show that this strain is metal-dependent and provides information about the adaptable tolerance of organisms in superfund sites as well as giving a basis for future bioremediation development utilizing H. anomala.

Roles of Endophytic Fungi Isolated from Mangifera indica L. in Promoting Plant Growth

Endophytic fungi have been shown to synthesize bioactive secondary metabolites, some of which promote plant growth through various mechanisms. In our previous study, endophytic fungi were isolated from mango trees (Mangifera indica L.). The present study examined fifty endophytic fungal isolates for mineral solubilization activity, ammonia production, and siderophore production. It was shown that these isolates could produce phytohormones indole-3-acetic acid and gibberellic acid, as well as inhibit plant pathogens, specifically Colletotrichum gloeosporioides and Lasiodiplodia theobromae. The results showed that all the isolated fungal endophytes exhibited various activities. Based on the findings, two fungal endophytes-Aureobasidium pullulans CY.OS 13 and Aspergillus tamarii CY.OS 144-were selected for dual inoculation in chili plants under pot-scale conditions to investigate their potential to improve growth-related traits such as seed germination, shoot and root length, biomass, and chlorophyll content. Seed treated with A. pullulans CY.OS 13 and/or A. tamarii CY.OS 144 showed a significant (p < 0.05) increase in seed germination and growth parameters of chili plants grown under pot-scale conditions. Particularly, chili plants whose seeds were injected with a combination of the two selected endophytic fungi showed the highest plant development traits. Therefore, the selected endophytic fungi have the potential to be used as biofertilizers, especially when combined. They could eventually replace chemical fertilizers because they are environmentally friendly, beneficial to humans, and can even promote sustainable agriculture.

Identification of microorganisms from fermented biowaste and the potential for wastewater treatment

Food loss or waste is a far-reaching problem and has indeed become a worrying issue that is growing at an alarming rate. Fruits and vegetables are lost or wasted at the highest rate among the composition of food waste. Furthermore, the world is progressing toward sustainable development; hence, an efficient approach to valorise fruit and vegetable waste (FVW) is necessary. A simple phenotypic characterisation of microbiota isolated from the fermented FVW was conducted, and its effectiveness toward wastewater treatment was investigated. Presumptive identification suggested that yeast is dominant in this study, accounting for 85% of total isolates. At the genus level, the enriched medium's microbial community consists of Saccharomyces, Bacillus and Candida. Ammonium in the wastewater can enhance certain bacteria to grow, such as lactic acid bacteria, resulting in decreased NH₄⁺ concentration at the end of the treatment to 0.5 mg/L. In addition, the fermented biowaste could reduce PO₄^3- by 90% after the duration of treatment. Overall, FVW is a valuable microbial resource, and the microbial population enables a reduction in organic matter such as NH₄⁺ and PO₄^3-. This study helps explore the function and improve the effectiveness of utilising biowaste by understanding the microorganisms responsible for producing eco-enzyme.

Molecular and Physiological Diversity of Indigenous Yeasts Isolated from Spontaneously Fermented Wine Wort from Ilfov County, Romania

(1) Background: Wine yeast research offers the possibility of isolating new strains with distinct metabolic properties due to the geographical location of the vineyard and the processes used in winemaking. Our study deals with the isolation and identification of six yeasts from spontaneously fermented wine wort from Romania and their characterization as new potential starter culture for traditional beverages, for food industry or biomedicine. (2) Materials and methods: The isolates were identified using conventional taxonomy tests, phenotypic phylogeny analysis (Biolog YT), MALDI-TOF mass spectrometry, PCR-RFLP, and sequencing of the ITS1-5,8S-ITS2 rDNA region. The capacity of the yeasts to grow under thermal, ionic, and osmotic stress was determined. The safe status was confirmed by testing virulence and pathogenicity factors. Assays were performed in order to evaluate the growth inhibition of Candida strains and determine the antimicrobial mechanism of action. (3) Results and discussions: The yeast isolates were identified as belonging to the Metschinikowia, Hanseniaspora, Torulaspora, Pichia, and Saccharomyces genera. All the isolates were able to develop under the tested stress conditions and were confirmed as safe. With the exception of S. cerevisiae CMGB-MS1-1, all the isolates showed good antimicrobial activity based on competition for iron ions or production of killer toxins. (4) Conclusions: The results revealed the resistance of our yeasts to environmental conditions related to industrial and biomedical applications and their high potential as starter cultures and biocontrol agents, respectively.

Mutualism between Gut-Borne Yeasts and Their Host, Thaumatotibia leucotreta, and Potential Usefulness in Pest Management

Thaumatotibia leucotreta is endemic to southern Africa and is highly significant for various fruit industries, including the South African citrus industry, due to its classification as a phytosanitary pest. Mutualistic associations between C. pomonella, closely related to T. leucotreta, and yeasts have previously been described and reported to reduce larval mortality and enhance larval development. Here, we determined which yeast species occur naturally in the gut of T. leucotreta larvae and investigated whether any of the isolated yeast species affect their behaviour and development. Navel oranges infested with T. leucotreta larvae were collected from geographically distinct provinces in South Africa, and the larvae were processed for analysis of naturally occurring associated yeasts. Six yeast species were isolated and identified from the guts of these T. leucotreta larvae via PCR amplification and sequencing of the ITS region of rDNA and D1/D2 domain of large ribosomal subunit. Larval development and attraction assays were conducted, and T. leucotreta larvae that fed on Navel oranges inoculated with yeast had accelerated developmental periods and reduced mortality rates. Neonate T. leucotreta were also attracted to YPD broth cultures inoculated with yeast for feeding. Oviposition preference assays were conducted with adult T. leucotreta females. Navel oranges inoculated with yeast were shown to influence the oviposition preference of adult females. Yeasts harbour the potential for use in biocontrol, especially when combined with other well-established control methods. This study provides a platform for future research into incorporating yeast with current biological control agents as a novel option for controlling T. leucotreta in the field.

Yeasts Associated with Various Amazonian Native Fruits

Yeasts, commonly present on the surface of fruits, are of industrial interest for the production of enzymes, flavorings, and bioactive compounds, and have many other scientific uses. The Amazonian rainforest may be a good source of new species or strains of yeasts, but their presence on Amazonian fruits is unknown. The aim of this study was to identify and characterize yeasts isolated from Amazonian native fruits using molecular and phenotypic methods. In total, 81 yeast isolates were obtained from 10 fruits species. Rep-PCR showed 29 strain profiles. Using a combination of restriction-fragment length polymorphism (RFLP) of the 5.8S-ITS region and D1/D2 sequencing of the 26S rRNA gene, 16 species were identified belonging to genera Candida, Debaryomyces, Hanseniaspora, Kodamaea, Martiniozyma, and Meyerozyma. The most dominant species were Candida tropicalis, Debaryomyces hansenii, Hanseniaspora opuntiae, and Hanseniaspora thailandica. H. opuntiae and H. thailandica showed the highest number of the strain profiles. Phenotypic profiles were variable between species, and even among strains. Screening for hydrolases showed lipolytic activity in only one isolate, while proteolytic, cellulolytic and amylolytic capabilities were not detected. Yeast presence among fruits varied, with cidra (Citrus medica) and ungurahui (Oenocarpus bataua) having the highest number of species associated. This investigation broadens the understanding and possible biotechnological uses of yeast strains obtained from Amazonian native fruits.

Yeasts, commonly present on the surface of fruits, are of industrial interest for the production of enzymes, flavorings, and bioactive compounds, and have many other scientific uses. The Amazonian rainforest may be a good source of new species or strains of yeasts, but their presence on Amazonian fruits is unknown. The aim of this study was to identify and characterize yeasts isolated from Amazonian native fruits using molecular and phenotypic methods. In total, 81 yeast isolates were obtained from 10 fruits species. Rep-PCR showed 29 strain profiles. Using a combination of restriction-fragment length polymorphism (RFLP) of the 5.8S-ITS region and D1/D2 sequencing of the 26S rRNA gene, 16 species were identified belonging to genera Candida, Debaryomyces, Hanseniaspora, Kodamaea, Martiniozyma, and Meyerozyma. The most dominant species were Candida tropicalis, Debaryomyces hansenii, Hanseniaspora opuntiae, and Hanseniaspora thailandica. H. opuntiae and H. thailandica showed the highest number of the strain profiles. Phenotypic profiles were variable between species, and even among strains. Screening for hydrolases showed lipolytic activity in only one isolate, while proteolytic, cellulolytic and amylolytic capabilities were not detected. Yeast presence among fruits varied, with cidra (Citrus medica) and ungurahui (Oenocarpus bataua) having the highest number of species associated. This investigation broadens the understanding and possible biotechnological uses of yeast strains obtained from Amazonian native fruits.

Molecular identification and performance evaluation of wild yeasts from different Ethiopian fermented products

Different types of yeasts and lactic acid bacteria dominate in spontaneously fermented products (food, beverages, and condiments) that are commonly consumed in Ethiopia. The aim of this study was to identify efficient fermentative yeasts from fermented foods, fermented beverages, honey and molasses using genotypic methods. Out of the 70 samples tested, 180 distinct wild yeast isolates were recovered. A total of 23 isolates were selected for genomic analysis based on their basis of biomass yield, fermentation capacity, and leavening performance. The nucleotide sequence analysis of the internal transcribed spacer ITS-5.8S rDNA region revealed that the indigenous yeast isolates had close relatedness to Saccharomyces cerevisiae, Candida humilis, Kazachstania bulderi, Pichia fermentans and Pichia kudriavzevii with greater than 97% nucleotide similarity. The study shows a high diversity of indigenous wild yeasts in fermented products and that potent strains had higher biomass yield, good gas production and remarkable leavening capacity that indicates their inherent potential for use in the baking industry.

Occurrence and Molecular Identification of Wild Yeasts from Jimma Zone, South West Ethiopia

Yeasts are common inhabitants of most fruit trees' rhizospheres and phyllospheres. Wild yeasts are the major driving force behind several modern industrial biotechnologies. This study focused on determining the occurrence and frequency of wild yeasts associated with domestic and wild edible tree barks, fruits, and rhizosphere soil samples collected over two seasons (i.e., spring and summer) in South West Ethiopia. A total of 182 yeast strains were isolated from 120 samples. These strains belonged to 16 genera and 27 species as identified based on the sequence analysis of the D1/D2 domain of the large subunit (26S) ribosomal RNA gene. Candida blattae, Pichia kudriavzevii, Candida glabrata, Saccharomyces cerevisiae, and Candida humilis were the most dominant yeast species isolated from the bark samples. Only Pichia kudriavzevii was regularly detected from the bark, rhizosphere, fruit, and sugarcane samples. The retrieval of yeasts from bark samples was more frequent and diverse than that of soil, fruits, and sugarcane. The frequency of detection of yeasts during the spring was significantly higher than in the summer season. However, there was no significant seasonal variation in the frequency of detection of yeast species between the rhizosphere and phyllosphere samples.

Diversity and enzymatic profiles of indigenous yeasts isolated from three types of palm wines produced in Côte d'Ivoire

AIMS

To investigate the genotypic diversity and enzymatic activity of yeast flora isolated from spontaneous fermenting saps of various palm trees (Borassus aethiopum, Raphia hookeri, Elaeis guineensis) tapped for palm wines.

METHODS AND RESULTS

PCR-restriction fragment length polymorphism of ITS-5.8S rDNA combined to 26S rRNA gene and/or the partial ACT1 gene sequencing were applied for yeast characterization, and their enzymatic profiles assessed by using API ZYM kits. Thirteen genera and 23 species were identified, with the highest diversity (14 species) in raffia wine. Saccharomyces cerevisiae was dominant and common to all palm wines. Some potentially pathogenic yeasts were also isolated. The majority of tested strains displayed high amylo-peptidase, phosphatase, β-glucosidase and α-glucosidase activities and esterase activity.

CONCLUSIONS

Diverse yeast species colonized palm wines, among which some were related to a specific type of wine and the majority of them have the ability to digest starch, sugar, protein or lipid.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is a first step in understanding the significance of indigenous yeast flora of palm wines from Côte d'Ivoire. This knowledge is important as a tool for establishing new indigenous yeast collection; which could be used for the product quality improvement and as enzyme sources for biotechnological purposes.

Yeasts and bacteria associated with kocho, an Ethiopian fermented food produced from enset (Ensete ventricosum)

Enset (Ensete ventricosum) is the basis of the staple food consumed by about 20% of the Ethiopian population. Kocho is one of the food products generated from enset by spontaneous fermentation of decorticated and pulverized pseudostem and corm sections. We isolated culturable microbes associated with kocho from different stages of fermentation. Twelve yeast species, six lactic acid bacteria (LABs) species and eleven species of aerobic bacteria were identified by sequencing ITS/D1D2 regions of 26S rDNA of yeasts and 16S rDNA of bacteria, respectively. More yeast species were identified in fresh (fermented for 2–5 days) kocho, compared to long-term (7–12 months) fermented kocho, while we observed an opposite trend for LABs. In fresh kocho, the most frequently isolated yeast species were Pichia exigua, Galactomyces geotrichum, and Pichia fermentans. From mid-term (3–4 months) kocho most frequently Candida cabralensis, G. geotrichum, and Candida ethanolica were isolated. In the long-term fermentations, the most frequently isolated yeast was Saturnispora silva. Lactobacillus plantarum was the most frequently isolated LAB in both fresh and mid-term kocho. In long-term fermented kocho, Acetobacter pasteurianus and L. plantarum were most frequently isolated. L. plantarum was consistently isolated from all the three stages of fermentation. Aerobic bacteria in fresh kocho were mostly gram-negative, with Raoultella planticola and Pantoea agglomerans being the most frequently isolated species. In long-term fermented kocho, mainly gram-positive, spore-forming bacteria of the genus Bacillus were found, among them also species of the Bacillus cereus group, Bacillus anthracis and Bacillus thurigiensis.

Diversity of Yeasts and Molds by Culture-Dependent and Culture-Independent Methods for Mycobiome Surveillance of Traditionally Prepared Dried Starters for the Production of Indian Alcoholic Beverages

Marcha, thiat, dawdim, hamei, humao, khekhrii, chowan, and phut are traditionally prepared dried starters used for production of various ethnic alcoholic beverages in North East states of India. The surveillance of mycobiome associated with these starters have been revealed by culture-dependent methods using phenotypic and molecular tools. We identified Wickerhamomyces anomalus, Pichia anomala, Saccharomycopsis fibuligera, Pichia terricola, Pichia kudriavzevii, and Candida glabrata by ITS-PCR. The diversity of yeasts and molds in all 40 samples was also investigated by culture-independent method using PCR-DGGE analysis. The average distributions of yeasts showed Saccharomyces cerevisiae (16.5%), Saccharomycopsis fibuligera (15.3%), Wickerhamomyces anomalus (11.3%), S. malanga (11.7%), Kluyveromyces marxianus (5.3%), Meyerozyma sp. (2.7%), Candida glabrata (2.7%), and many strains below 2%. About 12 strains of molds were also identified based on PCR-DGGE analysis which included Aspergillus penicillioides (5.0%), Rhizopus oryzae (3.3%), and sub-phylum: Mucoromycotina (2.1%). Different techniques used in this paper revealed the diversity and differences of mycobiome species in starter cultures of India which may be referred as baseline data for further research.

Genetic Polymorphism in Wine Yeasts: Mechanisms and Methods for Its Detection

The processes of yeast selection for using as wine fermentation starters have revealed a great phenotypic diversity both at interspecific and intraspecific level, which is explained by a corresponding genetic variation among different yeast isolates. Thus, the mechanisms involved in promoting these genetic changes are the main engine generating yeast biodiversity. Currently, an important task to understand biodiversity, population structure and evolutionary history of wine yeasts is the study of the molecular mechanisms involved in yeast adaptation to wine fermentation, and on remodeling the genomic features of wine yeast, unconsciously selected since the advent of winemaking. Moreover, the availability of rapid and simple molecular techniques that show genetic polymorphisms at species and strain levels have enabled the study of yeast diversity during wine fermentation. This review will summarize the mechanisms involved in generating genetic polymorphisms in yeasts, the molecular methods used to unveil genetic variation, and the utility of these polymorphisms to differentiate strains, populations, and species in order to infer the evolutionary history and the adaptive evolution of wine yeasts, and to identify their influence on their biotechnological and sensorial properties.

Comparison of DNA-based techniques for differentiation of production strains of ale and lager brewing yeast

AIMS

Brewing yeasts are classified into two species-Saccharomyces pastorianus and Saccharomyces cerevisiae. Most of the brewing yeast strains are natural interspecies hybrids typically polyploids and their identification is thus often difficult giving heterogenous results according to the method used. We performed genetic characterization of a set of the brewing yeast strains coming from several yeast culture collections by combination of various DNA-based techniques. The aim of this study was to select a method for species-specific identification of yeast and discrimination of yeast strains according to their technological classification.

METHODS AND RESULTS

A group of 40 yeast strains were characterized using PCR-RFLP analysis of ITS-5·8S, NTS, HIS4 and COX2 genes, multiplex PCR, RAPD-PCR of genomic DNA, mtDNA-RFLP and electrophoretic karyotyping. Reliable differentiation of yeast to the species level was achieved by PCR-RFLP of HIS4 gene. Numerical analysis of the obtained RAPD-fingerprints and karyotype revealed species-specific clustering corresponding with the technological classification of the strains. Taxonomic position and partial hybrid nature of strains were verified by multiplex PCR. Differentiation among species using the PCR-RFLP of ITS-5·8S and NTS region was shown to be unreliable. Karyotyping and RFLP of mitochondrial DNA evinced small inaccuracies in strain categorization.

CONCLUSIONS

PCR-RFLP of HIS4 gene and RAPD-PCR of genomic DNA are reliable and suitable methods for fast identification of yeast strains. RAPD-PCR with primer 21 is a fast and reliable method applicable for differentiation of brewing yeasts with only 35% similarity of fingerprint profile between the two main technological groups (ale and lager) of brewing strains.

SIGNIFICANCE AND IMPACT OF THE STUDY

It was proved that PCR-RFLP method of HIS4 gene enables precise discrimination among three technologically important Saccharomyces species. Differentiation of brewing yeast to the strain level can be achieved using the RAPD-PCR technique.

Inactivation of spoiling microorganisms in apple juice by a combination of essential oils’ constituents and physical treatments

A combination of different hurdles, such as mild heat (54 ℃ for 10 min) or pulsed electric field (25 pulses; 25 kV/cm; 3.35 kJ/cm per pulse) treatments and essential oils constituents (carvacrol, citral, and (+)-limonene), to reduce spoiling bacteria and yeasts in apple juice was evaluated. For this purpose, the heat and pulsed electric field resistances of five strains of Leuconostoc spp. and five Saccharomyces spp. strains were assayed, achieving different inactivation levels for each treatment and strain. For instance, Leuconostoc fallax 74, the most heat-resistant strain, was the second-most sensitive strain to pulsed electric field. The most resistant strains were exposed to combined processes of heat or pulsed electric field and 0.2 µl/ml essential oils constituents. The combination of heat and essential oils constituents proved to be synergistic against both microorganisms in apple juice. The most effective was the combination of mild heat and carvacrol, which caused the inactivation of 99% of L. fallax 74 and 99.99% of Saccharomyces cerevisiae CECT 1172 cells. Therefore, this study shows the great potential of carvacrol, citral, and (+)-limonene in combined treatments with mild heat to achieve a higher degree of inactivation of spoiling microorganisms in apple juice, and thus, to extend its shelf life.

Saccharomyces eubayanus and Saccharomyces uvarum associated with the fermentation of Araucaria araucana seeds in Patagonia

Mudai is a traditional fermented beverage, made from the seeds of the Araucaria araucana tree by Mapuche communities. The main goal of the present study was to identify and characterize the yeast microbiota responsible of Mudai fermentation as well as from A. araucana seeds and bark from different locations in Northern Patagonia. Only Hanseniaspora uvarum and a commercial bakery strain of Saccharomyces cerevisiae were isolated from Mudai and all Saccharomyces isolates recovered from A. araucana seed and bark samples belonged to the cryotolerant species Saccharomyces eubayanus and Saccharomyces uvarum. These two species were already reported in Nothofagus trees from Patagonia; however, this is the first time that they were isolated from A. araucana, which extends their ecological distribution. The presence of these species in A. araucana seeds and bark samples, led us to postulate a potential role for them as the original yeasts responsible for the elaboration of Mudai before the introduction of commercial S. cerevisiae cultures. The molecular and genetic characterization of the S. uvarum and S. eubayanus isolates and their comparison with European S. uvarum strains and S. eubayanus hybrids (S. bayanus and S. pastorianus), allowed their ecology and evolution us to be examined.

Sequencing-based analysis of the bacterial and fungal composition of kefir grains and milks from multiple sources

Kefir is a fermented milk-based beverage to which a number of health-promoting properties have been attributed. The microbes responsible for the fermentation of milk to produce kefir consist of a complex association of bacteria and yeasts, bound within a polysaccharide matrix, known as the kefir grain. The consistency of this microbial population, and that present in the resultant beverage, has been the subject of a number of previous, almost exclusively culture-based, studies which have indicated differences depending on geographical location and culture conditions. However, culture-based identification studies are limited by virtue of only detecting species with the ability to grow on the specific medium used and thus culture-independent, molecular-based techniques offer the potential for a more comprehensive analysis of such communities. Here we describe a detailed investigation of the microbial population, both bacterial and fungal, of kefir, using high-throughput sequencing to analyse 25 kefir milks and associated grains sourced from 8 geographically distinct regions. This is the first occasion that this technology has been employed to investigate the fungal component of these populations or to reveal the microbial composition of such an extensive number of kefir grains or milks. As a result several genera and species not previously identified in kefir were revealed. Our analysis shows that the bacterial populations in kefir are dominated by 2 phyla, the Firmicutes and the Proteobacteria. It was also established that the fungal populations of kefir were dominated by the genera Kazachstania, Kluyveromyces and Naumovozyma, but that a variable sub-dominant population also exists.

Yeast community associated with the solid state fermentation of traditional Chinese Maotai-flavor liquor

Yeasts are the most important group of microorganisms contributing to liquor quality in the solid-state fermentation process of Chinese Maotai-flavor liquor. There occurred a complex yeast community structure during this process, including stages of Daqu (the starter) making, stacking fermentation on the ground and liquor fermentation in the pits. In the Daqu making stage, few yeast strains accumulated. However, the stacking fermentation stage accumulated nine yeast species with different physio-biochemical characteristics. But only four species kept dominant until liquor fermentation, which were Zygosaccharomyces bailii, Saccharomyces cerevisiae, Pichia membranifaciens, and Schizosaccharomyces pombe, implying their important functions in liquor making. The four species tended to inhabit in different locations of the stack and pits during stacking and liquor fermentation, due to the condition heterogeneity of the solid-state fermentation, including the different fermentation temperature profiles and oxygen density in different locations. Moreover, yeast population was much larger in the upper layer than that in the middle and bottom layers in liquor fermentation, which was in accordance with the profile of reducing sugar consumption and ethanol production. This was a systematical investigation of yeast community structure dynamics in the Maotai-flavor liquor fermentation process. It would be of help to understand the fermentative mechanism in solid-state fermentation for Maotai-flavor liquor.

Saccharomyces unisporus: Biotechnological Potential and Present Status

 The yeast species of the Saccharomyces genus have a long history of traditional applications and beneficial effects. Among these presence of the Saccharomyces unisporus has been documented in various dairy products and has become a subject of interest and great importance. S. unisporus has shown a significant role in the ripening of cheese and production of fermented milk products such as kefir and koumiss. The absence of pseudohyphae during the life cycle of S. unisporus is an indication of nonpathogenicity. Significance has been laid on the presence of S. unisporus in food-grade products and a close proximity of S. unisporus to S. florentinus and both of these species are accepted by the International Dairy Federation and the European Food and Feed Cultures Association for food and feed applications. Since over the years, S. unisporus has already become a part of various dairy products, S. unisporus can be considered as a potential candidate for generally regarded as safe status. S. unisporus has the capacity to convert ketoisophorone to levodione, which is an important pharmaceutical precursor. S. unisporus are considered as the potential producers of farnesol which eventually controls filamentation of pathogenic microorganisms. Apart from that, S. unisporus produces certain omega unsaturated fatty acids which combat diseases. Henceforth, the areas which S. unisporus can be possibly exploited for its useful intermediates are the enzymes and fatty acids it produces. In this context, this review attempts to describe and discuss the ubiquity of S. unisporus in food products, cellular composition, regulatory pathways, and its synthesis of fatty acids and enzymes.

Epidemiology of Rhodotorula: an emerging pathogen

This is an updated paper focusing on the general epidemiological aspects of Rhodotorula in humans, animals, and the environment. Previously considered nonpathogenic, Rhodotorula species have emerged as opportunistic pathogens that have the ability to colonise and infect susceptible patients. Rhodotorula species are ubiquitous saprophytic yeasts that can be recovered from many environmental sources. Several authors describe the isolation of this fungus from different ecosystems, including sites with unfavourable conditions. Compared to R. mucilaginosa, R. glutinis and R. minuta are less frequently isolated from natural environments. Among the few references to the pathogenicity of Rhodotorula spp. in animals, there are several reports of an outbreak of skin infections in chickens and sea animals and lung infections and otitis in sheep and cattle. Most of the cases of infection due to Rhodotorula in humans were fungemia associated with central venous catheter (CVC) use. The most common underlying diseases included solid and haematologic malignancies in patients who were receiving corticosteroids and cytotoxic drugs, the presence of CVC, and the use of broad-spectrum antibiotics. Unlike fungemia, some of the other localised infections caused by Rhodotorula, including meningeal, skin, ocular, peritoneal, and prosthetic joint infections, are not necessarily linked to the use of CVCs or immunosuppression.

Role of social wasps in Saccharomyces cerevisiae ecology and evolution

Saccharomyces cerevisiae is one of the most important model organisms and has been a valuable asset to human civilization. However, despite its extensive use in the last 9,000 y, the existence of a seasonal cycle outside human-made environments has not yet been described. We demonstrate the role of social wasps as vector and natural reservoir of S. cerevisiae during all seasons. We provide experimental evidence that queens of social wasps overwintering as adults (Vespa crabro and Polistes spp.) can harbor yeast cells from autumn to spring and transmit them to their progeny. This result is mirrored by field surveys of the genetic variability of natural strains of yeast. Microsatellites and sequences of a selected set of loci able to recapitulate the yeast strain's evolutionary history were used to compare 17 environmental wasp isolates with a collection of strains from grapes from the same region and more than 230 strains representing worldwide yeast variation. The wasp isolates fall into subclusters representing the overall ecological and industrial yeast diversity of their geographic origin. Our findings indicate that wasps are a key environmental niche for the evolution of natural S. cerevisiae populations, the dispersion of yeast cells in the environment, and the maintenance of their diversity. The close relatedness of several wasp isolates with grape and wine isolates reflects the crucial role of human activities on yeast population structure, through clonal expansion and selection of specific strains during the biotransformation of fermented foods, followed by dispersal mediated by insects and other animals.

Evaluation of ITS PCR and RFLP for Differentiation and Identification of Brewing Yeast and Brewery 'Wild' Yeast Contaminants

A reference library of ITS PCR/RFLP profiles was collated and augmented to evaluate its potential for routine identification of domestic brewing yeast and known ‘wild’ yeast contaminants associated with wort, beer and brewing processes. This library contains information on band sizes generated by restriction digestion of the ribosomal RNA‐encoding DNA (rDNA) internal transcribed spacer (ITS) region consisting of the 5.8 rRNA gene and two flanking regions (ITS1 and ITS2) with the endonucleases CfoI, HaeIII, HinfI and includes strains from 39 non‐Saccharomyces yeast species as well as for brewing and non‐brewing strains of Saccharomyces. The efficacy of the technique was assessed by isolation of 59 wild yeasts from industrial fermentation vessels and conditioning tanks and by matching their ITS amplicon sizes and RFLP profiles with those of the constructed library. Five separate, non‐introduced yeast taxa were putatively identified. These included Pichia species, which were associated with conditioning tanks and Saccharomyces species isolated from fermentation vessels. Strains of the lager yeast S. pastorianus could be reliably identified as belonging to either the Saaz or Frohberg hybrid group by restriction digestion of the ITS amplicon with the enzyme HaeIII. Frohberg group strains could be further sub‐grouped depending on restriction profiles generated with HinfI.

Isolation and characterization of an acrylamide-degrading yeast Rhodotorula sp. strain MBH23 KCTC 11960BP

As well as for chemical and environmental reasons, acrylamide is widely used in many industrial applications. Due to its carcinogenicity and toxicity, its discharge into the environment causes adverse effects on humans and ecology alike. In this study, a novel acrylamide-degrading yeast has been isolated. The isolate was identified as Rhodotorula sp. strain MBH23 using ITS rRNA analysis. The results showed that the best carbon source for growth was glucose at 1.0% (w/v). The optimum acrylamide concentration, being a nitrogen source for cellular growth, was at 500 mg l(-1). The highest tolerable concentration of acrylamide was 1500 mg l(-1) whereas growth was completely inhibited at 2000 mg l(-1). At 500 mg l(-1), the strain MBH completely degraded acrylamide on day 5. Acrylic acid as a metabolite was detected in the media. Strain MBH23 grew well between pH 6.0 and 8.0 and between 27 and 30 °C. Amides such as 2-chloroacetamide, methacrylamide, nicotinamide, acrylamide, acetamide, and propionamide supported growth. Toxic heavy metals such as mercury, chromium, and cadmium inhibited growth on acrylamide.

Identification and characterization of bioemulsifier-producing yeasts isolated from effluents of a dairy industry

New bioemulsifier-producing yeasts were isolated from the biological wastewater treatment plant of a dairy industry. Of the 31 bioemulsifier-producing strains, 12 showed emulsifying activity after 2months of incubation, with E(24) values ranging from 7% to 78%. However, only Trichosporon loubieri CLV20, Geotrichum sp. CLOA40, and T. montevideense CLOA70 exhibited high emulsion-stabilizing capacity, with E(24) values of 78%, 67%, and 66%, respectively. These isolates were shown to induce a strong emulsion stabilizing activity rather than the reduction of the interfacial tension. These strains exhibited similar growth rates in the exponential growth phase, with a clear acceleration after 24h and stabilization of the activity after 144h. Emulsification and stability properties of the bioemulsifiers were compared to those of commercial surfactants after the addition of NaCl and exposure to temperature of 100 degrees C. The compounds produced by the isolates appeared to be lipid-polysaccharide complexes. Gas chromatograph analysis of the lipidic fraction of the bioemulsifiers from CLV20, CLOA40, and CLOA70 shows the prevalence of (9Z,12Z)-octadeca-9,12-dienoic acid, in concentrations of 42.8%, 25.9%, and 49.8%, respectively. The carbohydrate composition, as determined by GC-MS of their alditol acetate derivatives, showed a predominance of mannose, galactose, xylose and arabinose.

In vitro evaluation of the antimicrobial activity of eugenol, limonene, and citrus extract against bacteria and yeasts, representative of the spoiling microflora of fruit juices

This article reports on the investigation on the bioactivity of eugenol, limonene, and citrus extract against three bacteria (Lactobacillus plantarum, Lactobacillus brevis, and Bacillus coagulans) and three yeasts (Saccharomyces bayanus, Pichia membranifaciens, and Rhodotorula bacarum), representing the spoilage microflora of fruit juices. The experiments were performed with laboratory media by using a microdilution method. Data were fitted using the Gompertz equation, and the kinetic parameters were used to evaluate the MIC and the dose-dependent effect (at suboptimal doses for each essential oil). Citrus extract was the most effective essential oil, and the results suggested the following susceptibility hierarchy, from the most sensitive microorganism to the most resistant one (values in parentheses represent MICs): S. bayanus (2 ppm) > R. bacarum (3 ppm) > P. membranifaciens (5 ppm) > B. coagulans (cells, 20 ppm) > L. brevis (40 ppm) > L. plantarum (>40 ppm).

Species-specific variation in efficacy of yeast genomic DNA isolation techniques assessed using amplified fragment length polymorphism

Methods for isolating genomic DNA from yeasts are optimized for strains of Saccharomyces cerevisiae. The DNeasy tissue kit proved to be effective with 65 additional yeast species, providing 0.1 to 4.7 microg DNA/ml culture with sufficient purity to give reproducible amplified fragment length polymorphism (AFLP) profiles, but was unsuccessful with 13 other species. Two alternative yeast DNA purification kits, MasterPure and Y-DER, were effective with 6 of these and 2 additional species, leaving only 9 species that remained recalcitrant to yielding sufficient amounts of DNA with the required purity.

Lactic acid bacteria and yeasts associated with gowé production from sorghum in Bénin

AIMS

To identify the dominant micro-organisms involved in the production of gowé, a fermented beverage, and to select the most appropriate species for starter culture development.

METHODS AND RESULTS

Samples of sorghum gowé produced twice at three different production sites were taken at different fermentation times. DNA amplification by internal transcribed spacer-polymerase chain reaction of 288 lactic acid bacteria (LAB) isolates and 16S rRNA gene sequencing of selected strains revealed that the dominant LAB responsible for gowé fermentation were Lactobacillus fermentum, Weissella confusa, Lactobacillus mucosae, Pediococcus acidilactici, Pediococcus pentosaceus and Weissella kimchii. DNA from 200 strains of yeasts was amplified and the D1/D2 domain of the 26S rRNA gene was sequenced for selected isolates, revealing that the yeasts species were Kluyveromyces marxianus, Pichia anomala, Candida krusei and Candida tropicalis.

CONCLUSIONS

Gowé processing is characterized by a mixed fermentation dominated by Lact. fermentum, W. confusa and Ped. acidilactici for the LAB and by K. marxianus, P. anomala and C. krusei for the yeasts.

SIGNIFICANCE AND IMPACT OF THE STUDY

The diversity of the LAB and yeasts identified offers new opportunities for technology upgrading and products development in gowé production. The identified species can be used as possible starter for a controlled fermentation of gowé.