A. M. Glushakova

Seasonal dynamics of the structure of epiphytic yeast communities

The seasonal dynamics of the species structure of epiphytic yeasts on the leaves and in the flowers of 25 plant species was studied throughout the period of their vegetation. It was shown that, on average for the vegetation period, the composition of epiphytic yeast communities was nonspecific. The same species of epiphytic yeasts dominated on different plant species, irrespective of their taxonomic identity and ecological peculiarities. However, different species of yeasts exhibited different types of seasonal dynamics of relative abundance. Therefore, a combination of the dynamics of yeast species and the ontogenetic cycles of plants creates a pattern of the dynamics of the epiphytic yeast population, which is unique for each plant species. The species diversity of yeasts on the leaves of a plant is determined by the duration of its ontogenetic cycle: the longer the vegetation of a plant, the higher the diversity of the epiphytic yeasts population. The greatest diversity of epiphytic yeasts was revealed on the leaves of perennial hygrophytes and mesophytes; the minimal diversity, on ephemeroids and annuals with a short ontogenetic cycle.

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 of coevolving plant-microbial associations.

Characterization of yeast groupings in the phyllosphere of Sphagnum mosses

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.

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 Moscow and 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.

Seasonal Dynamics in a Yeast Population on Leaves of the Common Wood Sorrel 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.

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.

The seasonal dynamics of yeast communities in the rhizosphere of soddy-podzolic soils

The annual dynamics of the number and taxonomic composition of yeast was studied in the rhizosphere of two plant species (Ajuga reptans L. and Taraxacum officinale Wigg.) in a forb-birch forest on soddy-podzolic soil. Eurybiont phyllobasidial cryptococci and red-pigmented phytobionts Rhodotorula glutinis were found to predominate in the phyllosphere of these plants, whereas the typical pedobionts Cryptococcus terricola and Cr. podzolicus occurred on the surface of roots and in the rhizosphere. The seasonal changes in the number and species composition of the yeast communities in the rhizosphere were more smooth as compared to those in the phyllosphere. In the period of active vegetation of the plants, the phytobiont yeasts develop over their whole surface, including the rhizoplane. Their number on the aboveground parts of the plants was significantly lower than that of the pedobiont forms. Thus, the above-and underground parts of the plants significantly differed in the composition of the dominant species of epiphytic yeasts.

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 RELP analysis of 5.8S-ITS. Possible reasons for short-term increases in the number of saccharomycetes in plant phyllosphere are discussed.

The yeast Candida railenensis in the fruits of English oak (Quercus robur L.)

The cotyledons of whole intact acorns were shown to contain yeasts; their number increased sharply before acorn germination. The yeasts in the cotyledons are mainly represented by one species, Candida railenensis, with the number in the germinating cotyledons reaching 107 CFU/g. After germination or exocarp destruction, the cotyledons were colonized by the usual epiphytic and litter yeasts Cryptococcus albidus, Rhodotorula glutinis, and Cystofilobasidium capitatum.

Groups and Sources of Yeasts in House Dust

House dust contains bacteria, mycelial fungi, microarthropods, and yeasts. 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 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 candidiases. 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.