[Endophytic yeast fungi in plant storage tissues].

It was found that plant storage tissues (fleshy sugar-containing fruits, subsurface metamorphically altered plant organs (storage roots, tubers, etc.), and starch-containing seed lobes) nearly always contain yeasts that are able to actively reproduce in these tissues causing no visible damage. Within storage tissues, yeast cells were detected both in the intercellular space and inside plant cells. In the tissues of fleshy fruits, endophytic yeasts are represented by the same species as epiphytic ones; cryptococci of the order Filobasidiales and ascomycetes belonging to the genera Hanseniaspora and Metschnikowia are predominant. In subsurface plant organs, red pigmented basidiomycetous yeasts of the genus Rhodotorula prevail. Selective growth of representatives of one species, Candida railenensis, is typical of starch-containing storage tissues of seeds. The results obtained change the established notion of the distributional patterns of yeast fungi in natural habitats and suggest that internal storage tissues of plants can be considered as a new interesting model for studies ofcoevolving plant-microbial associations.

[Spacial structure of epiphytic yeast communities on fruits of Sorbus aucuparia L].

The subject of this research is epiphytic yeast communities that form on the surface of Sorbus aucuparia. The object is to make quantitative assessment of the yeast communities' differentiation of the same but distant substratum. Results of the factor variance nidicolous analysis demonstrated that with increase in distances, there are increases in the variation of total number and relative abundance of the dominant yeast communities. The average similarity between groups of single fruits (Sorensen's Quotient of Similarity) regularly decreased with distance. The results demonstrate that the number and structure of separate yeast groups depend not only on ecological factors but also on proximity to other communities. Such aggregation in the distribution of the microorganisms' species caused by migration and colonial resettlement should be taken into account when analyzing their diversity in natural habitats.

[Influence of Lumbricus terrestris earthworms on the structure of the yeast community of forest litter].

The taxonomic structure of yeast communities was studied in forest litter and soil, as well as in substrates transformed by the activity of Lumbricus terrestris earthworms (tree waste from the hole mouths, the gut contents, and coproliths). The activity of L. terrestris has a weak effect on the total yeast abundance but results in substantial changes in their taxonomic composition. The share of ascomycetous yeasts is significantly higher in the substrates associated with the activity of earthworms. The teleomorphic ascomycetes Williopsis saturnus were isolated from the gut contents. The effect of earthworms on the composition of the yeast community in the process of forest litter destruction is more markedly pronounced than seasonal changes.

[Seasonal dynamic of the numbers of epiphytic yeasts].

The numbers of epiphytic yeasts on the leaves and flowers of 25 plant species throughout their vegetation period was determined. The numbers of yeasts on the leaves were found to change regularly throughout the year. The average dynamics for all of the plant species investigated included an increase in yeast numbers during spring and summer with the maximum in late autumn and early winter. The character of the yeasts' dynamics depends on the ecological characteristics of the plants and the duration of the ontogenesis of their leaves and flowers. Three types of dynamics of epiphytic yeasts were revealed: year-round with an increase in autumn-winter, year-round without visible changes, and seasonal with a terminal increase for annual plants.

[Massive isolation and identification of Saccharomyces paradoxus yeasts from plant phyllosphere].

Year-round studies of epiphytic yeast communities revealed that the number of ascosporogenous yeasts of the genus Saccharomyces inhabiting living and decaying leaves of some plants increased considerably in certain short periods (at the beginning of summer and in winter). Massive isolation of saccharomycetes was performed from 11 plant species; earlier, these yeasts had been revealed mainly in sugar-rich substrates. The isolates were identified as Saccharomyces paradoxus based on their physiological properties and the lengths of restriction fragments of 5.8S-ITS rDNA. Possible reasons for short-term increases in the number of saccharomycetes in plant phyllosphere are discussed.

[Massive isolation of anamorphous ascomycete yeasts Candida oleophila from plant phyllosphere].

Many years of research has confirmed a wide distribution of anamorphous ascomycete yeasts in the phyllosphere of diverse plants of the Moscow oblast. Based on the standard morphological and physiological criteria, on the results of restriction analysis of the 5.8S-ITS rDNA region, and on the sequencing of the D1D2 region of 26S rDNA, these yeasts were identified as Candida oleophila Montrocher. Previous isolation of this species has been rare, possibly due to its incorrect identification. This species, together with phytobiotic basidiomycete yeasts, was shown to be dominant in the yeast epiphytic communities on the surface parts of plants. The relative abundance of C. oleophila is highest on plant fruits and increases significantly by the end of the vegetation period. Wide occurrence of this yeast species on fruits and in the phyllosphere may be related to its ability to compete with rapidly growing phytopathogenic fungi.

[The ratio of fungi and bacteria in the biomass of different types of soil determined by selective inhibition].

Tundra, chernozem (virgin and arable), sod-podzolic (coniferous forest, meadow, and arable), and grey forest (larch forest) soils were used to separate the contributions of fungi and bacteria to substrate-induced respiration (SIR) with the help of antibiotics. For soils with a high content of organic matter (tundra and chernozem: 12 and 8%, respectively), the procedure of selective inhibition of SIR has been optimized. The optimized procedure includes the application of high concentrations of streptomycin (50-120 mg/g of soil) and cycloheximide (50-80 mg/g of soil) and decreasing the weight of the analyzed soil sample. Soils under study have shown the predominant contribution of fungi (63-82%) to the total SIR. The fungal-bacterial ratio in the soils of natural ecosystems (0-5 cm, without litter) was 4.32, 2.19, 1.5, and 1.5 for tundra soil, virgin chernozem, coniferous (sod-podzolic soil), and larch (grey forest soil) forests, respectively. The lower layers of sod-podzolic (5-10 cm) and grey forest (48-58 cm) soils showed a decrease in the fungal and increase in the bacterial component in the total SIR.

[Interrelationships between yeast fungi and collembolans in soil].

The possibility of feeding on green and newly fallen leaves of the small-leaved lime Tilia cordata was studied for the collembolans Protaphorura armata and Vertagopus pseudocinereus. Young leaves grown under sterile conditions and almost free of yeast fungi were established to be toxic to the collembolan V. pseudocinereus: feeding on them led to the death of the animals. Leaves grown under natural conditions were nontoxic: when used by the collembolans as feed, they provided for collembolan growth and fecundity. Feeding preferences of the collembolans in relation to the yeasts attributed to different ecomorphs-epiphytes, litter saprophytes, pedobionts, and saccharobionts-were studied. Of the 24 yeast strains isolated from plant green parts, litter, and soil and assigned to eight species, no strain was revealed that was not used by the collembolans. However, certain yeast strains were preferable for the collembolans. The population of the V. pseudocinereus collembolans feeding on the yeast Rhodotorula glutinis (nss 31-4) exceeded that grown on Cryptococcus terricola (2044) 1.5-fold. Thus, the collembolans have feeding preferences in relation to yeast fungi, as was shown earlier for mycelial micromycetes. The possible mechanisms of the feeding preferences of the collembolans in relation to yeasts are discussed.

[Geographical races of certain species of ascomycetous yeasts in the Moscow and Novosibirsk regions].

Strains of three species of the ascomycetous yeasts Hanseniaspora guilliermondii, Torulaspora delbrueckii, and Debaryomyces hansenii, isolated from the above-ground parts of plants in similar biocenoses of distant geographic regions (Moscow and Novosibirsk regions), have been investigated. The strains in each species were indistinguishable with respect to phenotypic features and general DNA characteristics as determined by restriction analysis. However, comparison of the strains using PCR analysis with nonspecific primers revealed considerable intraspecific variability. From their electrophoretic patterns, the strains of the three species studied were found to cluster in accordance with the region of isolation. This phenomenon is interpreted as an example of the existence of geographical races in the major eurytopic species of yeasts.

[The latitude-zonal and spatial-successional trends in the distribution of yeasts].

The distribution of yeasts in natural habitats is analyzed in the different nature zones of the former USSR (from tundra to desert) using the results of long-term research. Yeast community structure is changing in parallel to different stages of plant debris decay as well as to latitude-zonal gradient. These changes are not fluctuating but trend ones. As mineralization of plant debris proceeds the availability of sugars decreases and habitat become more extremal for yeasts which are typical saccharolytics. It causes decrease in species abundance and species diversity. At the same time in zonal gradient the most significant changes take place in the relative abundance of dominant species, genera or higher taxonomic groups. The thermotolerant species occurred more often in the southern regions while psychrophilic species dominate in the north. Soil yeast communities become more polytrophic in the north latitudes where mineralization of organic matter is rather low. Species inhabiting climatic pessimum areas usually form chlamidospores.

[Community structure of yeast fungi in forest biogeocenoses]. / Struktura soobshchestv drozhzhevykh gribov v lesnykh biogeotsenozakh.

The results of longstanding studies of yeasts inhabiting soil, plant surface, and plant residues in typical subboreal forests of the European part of Russia are summarized. The abundance and species diversity of yeast communities in the array of substrates corresponding to succession stages in plant residues decomposition are shown to steadily decline. Each stage is characterized by its specific set of dominating species. The yeast diversity in forest biogeocenoses is shown to surpass that in other geographic zones. This manifests itself in a greater number of species occurring in similar arrays of substrates, in the absence of conspicuous dominants on the biogeocenotic level, and in a higher differentiation of the yeast population with respect to its habitat type. The forest yeast populations are also characterized by high diversity of yeasts of ascomycetous affinity and of the anamorphic stages of Taphrinales and Tremellales, as well as by the presence of typical pedobiont species (except Lipomyces spp.).

[Seasonal dynamics in a yeast population on the Oxalis acetosella L. leaves]. / Sezonnaia dinamika drozhzhevogo naseleniia list'ev Oxalis acetosella L.

Analysis of an epiphytic yeast population on the leaves of the evergreen common wood sorrel Oxalis acetosella L. throughout a year showed that the density and the species composition of this population underwent regular seasonal changes. There were almost no yeasts on the young spring leaves. However, the yeast population on the mature leaves tended to increase in the autumn, reaching a maximum after the formation of continuous snow cover. Then the yeast population on the leaves tended to decrease, reaching a minimum in the spring. The species diversity of the yeasts was maximum in the autumn. The population of the epiphytic yeast species Cystofilobasidium capitatum, Rhodotorula fujisanensis, Leucosporium scottii, and Cryptococcus flavus peaked in the autumn. On the other hand, the population of the widespread epiphytic species Cryptococcus laurentii on the wood sorrel leaves peaked in January. The relative abundance of the red-pigmented phytobionts Rhodotorula glutinis and Sporobolomyces roseus virtually did not change throughout the year. The relative abundance of the euribiotic species Cryptococcus albidus showed irregular monthly variations. The data obtained show that the epiphytic microbial population of various plants can be comprehensively studied only by analyzing this population throughout the vegetative period of the plants.

[Groups and sources of yeasts in house dust]. / Gruppirovki drozhzhei v kvartirnoi pyli i istochniki ikh formirovaniia.

House dust contains bacteria, mycelial fungi, microarthropods, and yeasts. The house dust samples collected in 25 apartments in Moscow and the Moscow region were found to contain yeasts belonging to the genera Candida, Cryptococcus, Debaryomyces, Rhodotorula, Sporobolomyces, and Trichosporon. The most frequently encountered microorganisms were typical epiphytic yeasts, such as Cryptococcus diffluens and Rhodotorula mucilaginosa, which are capable of long-term preservation in an inactive state. The direct source of epiphytic yeasts occurring in the house dust might be the indoor plants, which were contaminated with these yeasts, albeit to a lesser degree than outdoor plants. Along with the typical epiphytic yeasts, the house dust contained the opportunistic yeast pathogens Candida catenulata, C. guillermondii, C. haemulonii, C. rugosa, and C. tropicalis, which are known as the causal agents of candidiasis. We failed to reveal any correlation between the abundance of particular yeast species in the house dust, residential characteristics, and the atopic dermatitis of the inhabitants.

[A new yeast species, Candida aurita sp. nov., from oligotrophic bogs of Western Siberia]. / Novyi vid drozhzhei Candida aurita sp. nov. iz oligotrofnykh bolot Zapadnoi Sibiri.

Five anamorphous yeast strains of ascomycetous affinity with a specific mode of budding were isolated from raised bog soils of Bakcharskoe Bog (Tomsk oblast). According to their morphological and physiological properties, these strains belong to the genus Candida but differ from all species described previously. The level of DNA-DNA homology with species similar in the assimilation spectrum was as low as 7%. Based on these data, the new species Candida aurita sp. nov. is described.

[Yeast biodiversity in hydromorphic soils with reference to grass-Sphagnum swamp in Western Siberia and the hammocky tundra region( Barrow, Alaska)]. / Bioraznoobrazie drozzhei v gidromorfnykh pochvakh na primere traviano-sfagnovogo bolota (zapadnaia Sibir') i kochkarnoi tundry (Barrow, Aliaska).

The microbiological analysis of 78 samples taken from a boreal bog in Western Siberia and from a tundra wetland soil in Alaska showed the presence of 23 yeast species belonging to the genera Bullera, Candida, Cryptococcus, Debaryomyces, Hanseniaspora, Metschnikowia, Mrakia, Pichia, Rhodotorula, Saccharomyces, Sporobolomyces, Torulaspora, and Trichosporon. Peat samples from the boreal bog were dominated by eurytopic anamorphic basidiomycetous species, such as Rhodotorula mucilaginosa and Sporobolomyces roseus, and by the ascomycetous yeasts Candida spp. and Debaryomyces hansenii. These samples also contained two rare ascomycetous species (Candida paludigena and Schizoblastosporion starkeyi-henricii), which so far have been found only in taiga wetland soils. The wetland Alaskan soil was dominated by one yeast species (Cryptococcus gilvescens), which is a typical inhabitant of tundra soils. Therefore, geographic factors may serve for a more reliable prediction of yeast diversity in soils than the physicochemical or ecotopic parameters of these soils.

[A new yeast species Candida anutae sp.nov. from the fruiting bodies of agaricus]. / Novyi vid drozhzhei Candida anutae sp.nov. iz plodovykh tel agarikovykh gribov.

Among the yeasts isolated from the fruiting bodies of different species of agarics picked in forests near Moscow and Turku (Finland) in 1995-1998, populations of an earlier unknown species, morphologically similar to Metschnikowia lunata but differing from it by physiological characteristics and the absence of asci with spores, were constantly found. Description of the new species is given within the genus Candida Berkhout.