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In a model experiment, the transformation of microbial complexes of cultivated saprotrophic bacteria and yeasts during freezing-thawing was studied in various natural substrates that are used to create soil constructions for urban landscaping and for growing herbaceous plants. The number of saprotrophic bacteria and yeasts depended both on the type of substrate and on temperature changes during freezing-thawing. At the stage of freezing of peat and soil (arable horizon) to 0 and –5°C and at the subsequent stage of thawing to 0°C, a significant increase in yeast number was registered. The maximum number of yeasts in soil and peat was 5.1 log (CFU/g). In contrast to the number of yeasts, number of saprotrophic bacteria in soil and peat was characterized by a sharp decrease when the substrate temperature was negative and peaked at 19–22 and 10°C, respectively. The maximum bacterial number in soil and peat was 7.5 and 8.0 log (CFU/g), respectively. In sand, number of both saprotrophic bacteria and yeasts did not depend on the temperature and was 5.0 log (CFU/g) for bacteria and 3.4 log(CFU/g) for yeasts at all stages of the freezing-thawing cycles. In total, 15 saprotrophic bacterial species and 29 yeast species were isolated from different components of soil constructions. At the maximum temperature of freezing in the cycles (–5°C), three bacterial species with psychrophilic properties (Flavobacterium psychrophilum) and the ability to form endospores resistant to various adverse effects (Bacillus subtilis, B. megaterium) were isolated from soil and peat. Among the yeasts isolated from soil and peat at negative temperature and also having psychrophilic properties were Candida sake, Rhodotorula glutinis, Rh. mucilaginosa, and Solicoccozyma terricola. Bacteria with psychrophilic properties, F. psychrophilum and Pseudomonas fluorescens, as well as two species of bacilli, Bacillus subtilis and B. megaterium were revealed in sand at negative temperatures. Only one yeast species, Debaryomyces hansenii, capable of surviving stress conditions in the form of ascospores, was isolated from sand at –5°C. The effect of short-term temperature drops on the microbial communities’ number and diversity dynamics in soil constructions in a model experiment showed that specialized soil constructions were able to “tolerate” short-term temperature stress drops typical of the spring and autumn period, restoring the number of initial populations after cessation of the negative impacts. This also indicates development of the soil constructions in the process of functioning, rather than their rapid degradation.

Drosophila melanogaster fruit flies are an important model for studying the multifaceted interactions between a multicellular organism and its microbiome. The nature of these interactions is largely determined by the regular changes in abundance and composition of the microbiome that occur during the host’s life. The currently available data on age- and life cycle stage-related changes in the Drosophila microbiome relate mainly to its bacterial component, while little is known about such changes in the equally important yeast component. The present work describes the quantitative and qualitative composition of the yeast component of the D. melanogaster microbiome in three laboratory lines, reared under different conditions, at four developmental stages: late larvae and adults aged 1, 7, and 14 days after eclosion. In all three lines, the total yeast abundance changed similarly with the age of insects, with the highest and lowest yeast counts in 7- and 1-day adults, respectively. In the fly lines reared on moderately unfavorable substrates supplemented with 2 and 4% NaCl, the abundance and species diversity of yeasts at all four developmental stages was higher than in the flies reared on a standard (favorable) food substrate. Our results indicate the inconstancy of the yeast component of the D. melanogaster microbiome and its regular changes with the insect’s age, which must be taken into account when studying the relationships between symbiotic yeasts and their hosts.

Yeast number and species diversity in urban soils characterized by various intensities of anthropogenic impact in the southern cities of Russia (Krasnodar, Maykop, Simferopol, and Sochi) was investigated. The soils of botanical gardens and the reference soils in the vicinities of cities were used for comparison to reveal the degree of anthropogenic impact. The maximum yeast number was found in a layer of 0–20 cm in the urban soils of Sochi and Simferopol, where it was 5.7 ± 0.2 and 5.4 ± 0.01 log (CFU/g), respectively. The minimum number of yeasts, 2.0 ± 0.1 log (CFU/g), was characteristic of a 60–80-cm layer in the soils in the vicinities of all cities. The number of yeasts was shown to depend primarily on the depth and type of soil and to a lesser extent on location. A total of 20 yeast species were isolated from the studied soils: 10 ascomycetes and 10 basidiomycetes. All basidiomycete yeasts isolated from urban soils and control soils were typical representatives of pedobiont and epiphytic yeast complexes. In the soils of the major tourist cities of Sochi and Simferopol, a high relative abundance of ascomycete species Candida sake and Meyerozyma guilliermondii was found, which fundamentally distinguished the studied soils from the ones of Krasnodar and Maykop. The cities of Sochi and Simferopol are characterized by a higher anthropogenic load compared to Krasnodar and Maykop, which is associated not only with their high population, but also with a significant tourist load. Detection in urban soils of C. sake and M. guilliermondii which, according to some data, are clinically significant, was therefore consequential.

Relationship between symbiotic yeast and Diptera insects are studied mainly on fruit flies (Drosophilidae). Evolutionary experiments showed that changes in the composition of the yeast microbiota vectored by flies in their gut and on the body surface contributes to the adaptation of laboratory Drosophila populations to the high-salt growth medium. Although saline substrates are not commonly used by Drosophilidae in nature, species adapted to such substrates are known in other families of Diptera. Yeast communities associated with these species are studied insufficiently. This is the first report on the yeast communities associated with two Diptera species living near the White Sea, Paracoenia fumosa (Stenhammar, 1844) (Ephydridae) and Fucellia fucorum (Fallen, 1819) (Anthomyiidae). Their larvae develop in the coastal saline lagoons and in algae driven ashore. The P. fumosa yeast microbiota includes opportunistic species Pichia kluyveri Bedford ex Kudryavtsev, 1960 and P. kudriavzevii Boidin, Pignal, Besson, 1965 and is characterized by its highly variable abundance (the number of colony-forming units varies widely in different individuals). F. fucorum is characterized by a more stable yeast community, including species common in White Sea algae and coastal waters (Debaryomyces hansenii (Zopf) Lodder, Kreger-van Rij, 1952, Metschnikowia zobellii (van Uden, Castelo-Branco) van Uden, 1962, and M. bicuspidata (Metschnikoff) Kamienski, 1899). These two species of littoral flies shared no common yeast species. Moreover, none of the yeast species found in the littoral flies was detected in the evolutionary experiment on the adaptation of Drosophila to the high-salt growth medium (the similarity is limited only to the Pichia genus level). Contrasting differences in the yeast microbiome of two ecologically similar littoral species of Diptera may indicate, on the one hand, specificity, and, on the other, evolutionary plasticity of the relationship between salt-tolerant flies and yeast.

Yeast abundance and diversity were studied in the soils (topsoil) of Moscow city: urban soils under lawn vegetation and close to the areas of household waste disposal, as well as in zonal soddy-podzolic soils (retisols) in parks (Losiny Ostrov and Izmailovo). The numbers of soil yeasts were similar in all studied urban biocenoses (on average ~3.5 × 103 CFU/g). From all studied soils, 54 yeast species were isolated. The highest yeast diversity was found in the soils adjacent to the areas of household waste storage. Soils from different urban sites were found to have different ratios of ascomycetous and basidiomycetous yeasts: basidiomycetes predominated in urban soils under lawn vegetation, while in the areas close to the waste disposal sites their share was considerably lower. The differences between the studied urban soils were also found in the structure of soil yeast complexes. In urban soils with high anthropogenic impact, the isolation frequency of clinically important yeast species (Candida parapsilosis, C. tropicalis, Diutina catenulata, and Pichia kudriavzevii) was as high as 35% of all studied samples, while its share in the community was 17%. The factors responsible for development of specific features of yeast communities in various urban soils are discussed in the paper.

Yeast abundance and species diversity in the lichens collected at the Kindo Peninsula (Karelia) were studied. A total of 14 lichen species analyzed belonged to the genera Bryoria, Cladonia, Hypogymnia, Icmadophila, Nephroma, Peltigera, and Ramalina. Abundance of cultured yeasts in lichens was intermediate between soil and phyllosphere. The average yeast number on lichens was ~2.5 × 103 CFU/g, while it exceeded 8 × 103 CFU/g on plants and reached only 1 × 103 CFU/g in soil. Yeast population of different parts of Cladonia lichens was found to vary significantly in abundance, species diversity, and community structure. The highest yeast abundance and diversity were revealed in the growth zone. Fifteen yeast species were isolated from lichens, including 6 basidiomycetous and 9 ascomycetous ones. Unlike soils and plants, yeast population of lichens consisted mainly of ascomycetous species, with predominance of Candida sphagnicola and anamorphous yeasts of the genus Dothiora. These results show that yeasts from different taxonomic and ecological groups are a necessary component of lichens; conditions favoring the preservation and development of specific yeast communities differing from the typical soil and phyllosphere yeast complexes are formed in the lichens of northern taiga forests.

Abundance and taxonomic structure of yeast communities on the surface and in the tissues of various plants of the Nikitsky Botanical Garden was studied. A total of 22 yeast species were isolated, including rare and new species. Yeast numbers on the studied plant substrates were varied within a broad range (8 × 102‒2.5 × 107 CFU/g), reaching the maximum in Verbascum thapsus flowers, on the surface and inside the fruits of Rubus sp. and Ficus carica. Epiphytic and endophytic yeast communities of Ficus carica fruits were studied in dynamics, from fruit formation until their complete maturation and senescence. Specific properties of the yeast communities of the Nikitsky Botanical Garden plants and the features of the yeast communities from fig fruits are discussed in the paper.

The current state of scientific researches in lichen microbiology was reviewed. Analysis of the literature revealed the main areas and fundamental issues which refer to investigation of microbial consortia in lichen bodies. Special attention was focused on analysis of the prokaryotic community which plays a structural and functional role and is involved in metabolism and regulation of activity of the lichen symbiosis as a whole. In the review, for the first time the information on the yeast community, of which some members do not occur presently in other environmental substrates, was summarized. The data on the protozoa inhabiting lichen thalli were also provided. The reviewed literature enabled us to consider the growing and decaying thallus as a complex ecosystem with specific levels of regulation of abundance, taxonomic diversity, and activity of the members of five kingdoms: fungi, plants, protozoa, eubacteria, and archaea.

Yeast abundance and species diversity of endophytic complexes in galls (cecidia) formed on the leaves of Salix fragilis, Salix caprea, Quercus robur, Tilia cordata, and Ulmus laevis and the epiphytic yeast communities of undamaged leaves of these plants were studied. Dynamics of yeast abundance in the galls was significantly different from that of the epiphytic yeast communities. Maximum numbers of endophytic yeast cells in the galls (up to 104 CFU/g) were comparable to abundance of epiphytic yeasts. A total of 14 species of endophytic yeasts were isolated from galls of different plants. Ascomycetous yeasts were found to predominate in the insect galls on willows and oak, while basidiomycetous yeasts dominated in mite galls on linden and elm, as well as on plant leaves. These results indicate that gall formation may be considered not only as a bidirectional pathological process of the interaction between plants and invertebrates, but also as a process in which the endophytic microbial population of the galls plays an important role.

Yeast abundance and species diversity on the surface and in inner tissues of Malus domestica and Pyrus communis fruits under high anthropogenic impact in the city of Moscow (Russia) were studied. Results demonstrated that abundance of epiphytic yeasts on the fruits increased gradually, reaching the maximum of 3.2 × 10⁴ CFU/g on mature fruits. During summer, abundance of endophytes did not change significantly (variation near 2.5 × 10³ CFU/g) until complete maturation, while in September their numbers increased to 104 CFU/g. Basidiomycetous yeasts (Filobasidium wieringae, F. magnum, Rhodotorula glutinis, and Rhodosporidiobolus colostri) predominated on the fruit surface. Ascomycetous species were the most diverse group inside the fruits, which quantitatively increased through maturation. It was found that the share of opportunistic species Candida parapsilosis in internal tissues was significant during the entire period of fruit formation and development under anthropogenic impact in the city. Specific properties of epiphytic and endophytic yeast communities developing in natural ecological niches under synanthropic conditions and anthropogenic impact are discussed.

High performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) was applied to the comprehensive analysis of the ability of yeast strains to synthesize a plant hormone indole-3-acetic acid (IAA). A total of 124 strains (37 species) of yeasts isolated from various regions and substrates were studied. Testing of IAA production showed that 92% strains were capable of IAA synthesis. The results indicated that, in general, ascomycetous yeasts were more active auxin producers than basidiomycetous ones. Geographically, strains from tropical regions were the most active IAA producers. Analysis of the substrate variability of the strains showed higher auxin production (on average) by the yeasts isolated from plants compared to the soil isolates, indicating a specific regulatory role of the plant yeast population.

Yeast abundance and species diversity in the latex of rubber tree Hevea brasiliensis (Willd. ex Juss.) Mull. Arg., on its green leaves, and in soil below the plant were studied. The yeasts present in the fresh latex in numbers of up to 5.5 log(CFU/g) were almost exclusively represented by the species Candida heveicola. This species was previously isolated from Hevea latex in China. In the course of natural modification of the latex (turned from liquid to solid form), yeast diversity increased, while yeast abundance decreased. The yeasts in thickened and solidified latex were represented by typical epiphytic and ubiquitous species: Kodamea ohmeri, Debaryomyces hansenii, Rhodotorula mucilaginosa, and synanthropic species Candida parapsilosis and Cutaneotrichosporon arboriformis. The role of yeasts in latex modification at the initial stages of succession and their probable role in development of antifungal activity in the latex are discussed.

Yeast abundance and species diversity in the colonies of Formica aquilonia ants in birch-pine forbs forest, Novosibirsk oblast, Russia, was studied. The average yeast number in the anthill material was 10³-10⁴CFU/g, reaching 10⁵ CFU/g in the hatching chambers. Typical litter species (Trichosporon monilfiforme and Cystofilobasidium capitatum) were predominant in soil and litter around the anthills. Apart from these species, ascomycete species of the family Debaryomycetaceae, Debaryomyces hansenii and Schwanniomyces vanrijiae, were predominant in the anthill material. Yeast population of the ants consisted exclusively of the members of these two species. Thus, highly specific yeast communities formed in the colonies of Formica aquilonia ants differ from the communities of surrounding soil. These differences are an instance of environment-forming activity of the ants.

Yeast abundance and diversity in a mixed forest sod-podzol soil under Impatiens parviflora DC plants was studied in comparison with unimpaired aboriginal herbaceous plants typical of the Mid-Russian secondary, after-forest meadow. The study was carried out throughout the vegetation period. Standard microbiological plating techniques revealed 36 yeast species. Typical pedobiotic (Cryptococcus podzolicus, Wickerhamomyces anomalus) and eurybiotic yeast species (Rhodotorula mucilaginosa) predominated in both biotopes. The relative abundance of the autochthonous soil yeast species Cryptococcus podzolicus was higher in the soil under aboriginal herbs than under Impatiens parviflora. Sites with aboriginal vegetation were also characterized by high abundance of the pedogamous species Schwanniomyces castelli and Torulaspora delbrueckii. The share of yeastlike Trichosporon fungi with high hydrolytic activity was considerably higher under adventitious plants Impatiens parviflora, as well as in the previously studied soil under Heracleum sosnowskyi.

Long-term studies of yeast species diversity in the vineyards of the Republic of Dagestan using various isolation techniques and various substrates in the vertical tier dynamics revealed 38 species. The most diverse species complex including -80% of the isolated species was formed on the berries. A list of 160 yeast species isolated from grapes, spontaneously fermented fresh juice, and other vineyard substrates was compiled using the results of the present work and the literature data on yeast occurrence. Analysis of generalized data revealed considerable similarity in the taxonomic composition of yeasts from different countries and continents and made it possible to shift from the genus to the species characterization of the grape-associated yeast community.

Long-term microbiological investigation of the pollen of silver birch (Betula pendula) in the Moscow and Moscow oblast areas revealed that almost one-third of the analyzed samples contained the fungus identified by morphological, cultural, and molecular genetic techniques as Quambalaria cyanescens (de Hoog & G.A. de Vries) Z.W. de Beer, Begerow & R. Bauer. This species was previously known mostly as a symbiont of tropical plants of the genera Eucalyptus and Corymbia and have not been isolated in Russia. We revealed a close association between Quambalaria cyanescens and silver birch. The micromycete was regularly detected in pollen samples, as well as on the inside and outside of the aments, and on the surface of leaves and branches. It was never isolated from other plant species in the investigated area. The data on the morphological and cultural characteristics of the fungus, its cell ultrastructure, and occurrence are presented, as well as the phylogenetic analysis of the isolated strains.

Dynamics of abundance and diversity of epiphytic yeasts in entomophilic flowers of 28 species of meadow, forest, and cultivated plants throughout their blooming period was determined. The number of yeasts in the flowers was shown to increase gradually during the vegetation period, and reached the maximum during summer-autumn. The total abundance and ratio of the yeast species in the flowers depended entirely on the blooming time, rather than on the taxonomic position of the plants. Three stages of development of the entomophilic yeast complexes during the vegetation period may be discerned: predominance of eurybiont nonspecific species (Cryptococcus albidus, Debaryomyces hansenii) in spring, mass development of specific nectar-associated yeasts (Metschnikowia reukaufii) in summer, and their substitution by widespread epiphytic species (Rhodotorula mucilaginosa, Cryptococcus magnus) in autumn.

The fungus Fusarium sp. isolated from saline soil was identified by the ITS1-5.8S-ITS2 and the D1/D2 domains of LSU RNA as a member of the Fusarium incarnatum-equiseti species group. Its growth patterns on media with different NaCl concentrations indicated its adaptation as halotolerance. The mechanisms of halotolerance included accumulation of arabitol (a five-atom noncyclic polyol), a decreased sterols/phospholipids ratio, elevated level of phosphatidic acids in the phospholipids, and increased unsaturation of phospholipids, which was especially pronounced in the idiophase. The mechanisms of halotolerance of the mycelial fungus Fusarium sp. are discussed in comparison with yeasts and yeastlike fungi.

A fungus was isolated from aviation fuel and identified as Monascus floridanus P.F. Cannon & E.L. Barnard (FR827895) according to its morphological and genetic properties. The isolate has some properties that are unusual for the type strain, including a prominent stripe on one of the sides of the ascospores and occurrence, along with the known Basipetospora-type thallic conidia, of the phialophora-like spore formation. The isolated strain Monascus floridanus, like the known kerosene fungus Hormoconis resinae (Lindau) Arx & G.A. de Vries, is capable of active growth in aviation fuel.

Yeasts are a traditional model for investigation of eukaryotic genetics. Yeasts are also a convenient model for developing the principles of phylogenetic classification and the species concept due to the com� paratively small size of the group and the previously accumulated knowledge on both the phenotypic and molecular biological characteristics of yeast species. The main criteria for classification of yeast species have initially been morphological, with subsequent investigation of their physiological characteristics. The present stage, while considering all accumulated knowledge, is based on the application of molecular biological techniques, primarily, the analysis of con� servative rDNA regions. Until recently, the reference point for establishing the criterion of a phylogenetic species in yeasts has been the percentage of differences in the ribosomal genes, more specifically, in the D1/D2 domains of the 26S (LSU) rDNA [1]. Quite recently, another rDNA region, ITS, was chosen as such a universal barcode marker for the whole king� dom of Fungi [2]. However, a large amount of data indicates that in some cases, including yeasts, inde� pendent application of these two regions is not always applicable, so it is necessary to use them jointly [3]. Moreover, the level of differences in the ribosomal genes for differentiation between yeast species is being discussed [4]. It is impossible to solve this problem without taking into account all the possible deviations from the type strains, which are stored in collections as “standard” strains. The discovery of genetically diver� gent strains makes it possible to specify the phyloge� netic boundaries of the species, and also contributes to development of the understanding that a phylogenetic species is not something discrete; slight deviations are always possible, and their level is to be studied in the future. In 2012, in the course of the investigation of the yeasts associated with the Pleistocene bison (steppe bison) mummy found recently in permafrost in the lower reach of Anyui River (Chukotka, Russia), the strain Candida saitoana VKPM Y�3988 was isolated, which had substantially divergent rDNA nucleotide sequences, as well as certain specific phenotypic fea� tures. The strain was isolated from the wool sampled from the surface of the carcass. Its identification was carried out by analyzing the nucleotide sequences of

Several rare species and varieties of psychrophilic yeasts were isolated from the Sphagnum mosses and paludal vascular plants of Moscow oblast. Based on their 26S rDNA D1/D2 nucleotide sequences, they were assigned to the species Sterigmatosporidium polymorphum, Rhodotorula psychrophenolica, and Aureobasidium pullulans var. subglaciale. Thus, a new habitat of S. polymorphum was found and yeasts known previously only for the Alpine environments and the Arctic region have been isolated in the central regions of Russia for the first time.

Significant differences were revealed in the taxonomic structure of the epiphytic yeast communities formed on Sphagnum mosses and on the leaves of vascular plants. On mosses, low abundance of red yeasts was found (the most typical epiphytes on vascular plant leaves), along with a relatively high content and diversity of nonpigmented dimorphic basidiomycetes related to the order Leucosporidiales. The species composition of epiphytic yeasts from mosses is different from that of both forest and meadow grasses and of the parts of vascular plants submerged in the turf. The specific composition of the Sphagnum mosses yeast community is probably determined by the biochemical characteristics of this environment, rather than by the hydrothermal regime in the turf.