Yeasts and yeast-like organisms associated with fruits and blossoms of different fruit trees.

Yeasts are common inhabitants of the phyllosphere, but our knowledge of their diversity in various plant organs is still limited. This study focused on the diversity of yeasts and yeast-like organisms associated with matured fruits and fully open blossoms of apple, plum, and pear trees, during 2 consecutive years at 3 localities in southwest Slovakia. The occurrence of yeasts and yeast-like organisms in fruit samples was 2½ times higher and the yeast community more diverse than that in blossom samples. Only 2 species (Aureobasidium pullulans and Metschnikowia pulcherrima) occurred regularly in the blossom samples, whereas Galactomyces candidus, Hanseniaspora guilliermondii, Hanseniaspora uvarum, M. pulcherrima, Pichia kluyveri, Pichia kudriavzevii, and Saccharomyces cerevisiae were the most frequently isolated species from the fruit samples. The ratio of the number of samples where only individual species were present to the number of samples where 2 or more species were found (consortium) was counted. The occurrence of individual species in comparison with consortia was much higher in blossom samples than in fruit samples. In the latter, consortia predominated. Aureobasidium pullulans, M. pulcherrima, and S. cerevisiae, isolated from both the fruits and blossoms, can be considered as resident yeast species of various fruit tree species cultivated in southwest Slovakia localities.

Influence of pesticides on yeasts colonizing leaves.

The effect of nine different pesticides on the growth of yeasts isolated from the leaves of fruit and forest trees was investigated. Four insecticides (with the active ingredients: thiacloprid, deltamethrin, lambdacyhalothrin, and thiamethoxam) and five fungicides (with the effective substances: bitertanol, kresoxim-methyl, mancozeb, trifloxystrobin, and cupric oxychloride) were tested. The concentrations of chemicals were those recommended by the manufacturers for the spraying of trees. The yeast strains isolated from the leaves of fruit trees were not sensitive to any of the insecticides. The majority of yeast strains isolated from the leaves of forest trees were either not sensitive or only to a small extent. While Rhodotorula mucilaginosa and Pichia anomala were not affected by any insecticide, the strains of Cryptococcus laurentii and Rhodotorula glutinis showed the highest sensitivity. The effects of fungicides on the growth of isolated yeasts were more substantial. The fungicide Dithane DG (mancozeb) completely inhibited the growth of all yeasts. All strains isolated from fruit tree leaves were more resistant to the tested fungicides than those isolated from the leaves of forest trees. The most resistant strains from the leaves of fruit trees belonged to the species Metschnikowia pulcherrima, Pichia anomala, and Saccharomyces cerevisiae, whereas Cryptococcus albidus and C. laurentii, originating from the leaves of forest trees, showed the highest sensitivity to fungicides.

Geotrichum bryndzae sp. nov., a novel asexual arthroconidial yeast species related to the genus Galactomyces.

Ten strains of an asexual arthroconidial yeast species were isolated from Bryndza, a traditional Slovak artisanal sheep cheese, which was manufactured from raw milk during a 4-month summer production period at two Slovakian sites (the northern RuZomberok and the central-southern Tisovec areas). Sequence comparison of the D1/D2 domains of the large-subunit rRNA gene revealed that this yeast represents a novel species of the genus Geotrichum, which contains anamorphs of the ascogenous genus Galactomyces, for which the name Geotrichum bryndzae sp. nov. is proposed (type culture CCY 16-2-1T=NRRL Y-48450T=CBS 11176T). The novel species is most closely related to Geotrichum silvicola NRRL Y-27641T, although yeasts with identical or very similar sequences have been found throughout the world.

Yeasts colonizing the leaf surfaces.

The yeasts were isolated from the leaf surfaces of ten species of trees. The study site was a forest park (Zelezná Studnicka) of the Small Carpathians mountain range. One hundred and thirty seven yeast strains belonging to 13 genera were isolated from 320 samples of leaves and needles. Seventeen yeast species were isolated, but only seven occurred regularly: Aureobasidium pullulans, Cryptococcus laurentii, Pichia anomala, Metschnikowia pulcherrima, Saccharomyces sp., Lachancea thermotolerans, and Rhodotorula glutinis. The remaining species were isolated from the leaves and needles of three or less tree species. A. pullulans, Cr. laurentii, and P. anomala were the most frequently found species and they occurred on leaves and needles of all ten tree species. Saccharomyces sp. occurred in leaf samples collected from eight kinds of trees. M. pulcherrima and L. thermotolerans were found in samples collected from six species of trees. Both these species occurred almost always on the leaves of deciduous trees. Rh. glutinis was the most frequently isolated carotenoids producing species. We have found out that the ascomycetous and basidiomycetous species were present in the leaf samples in approximately equal frequency, contrary to the soil samples taken from this forest park, where the ascomycetous species were found rarely.

Killer activity of yeasts isolated from natural environments against some medically important Candida species.

Twenty-five yeast cultures, mainly of human origin, belonging to four pathogenic yeast species--Candida albicans, Candida krusei, Candida parapsilosis, and Candida tropicalis were tested for their sensitivity to ten basidiomycetous and eleven ascomycetous yeast species isolated from the water and soil environments and from tree leaves. The best killer activity among basidiomycetous species was exhibited by Rhodotorula glutinis, and R. mucilaginosa. The other carotenoid producing species Cystofilobasidium capitatum, Sporobolomyces salmonicolor, and S. roseus were active only against about 40% of the tested strains and exhibited weak activity. The broadest killer activity among ascomycetous yeasts was shown by the strains Pichia anomala and Metschnikowia pulcherrima. The species Debaryomyces castellii, Debaryomyces hansenii, Hanseniaspora guilliermondii, Pichia membranifaciens, and Williopsis californica did not show any killer activity. The best killer activity exhibited the strains isolated from leafy material. The lowest activity pattern was found among strains originating from soil environment.

One-pot synthesis of 2-C-glycosylated benzimidazoles from the corresponding methanal dimethyl acetals.

A series of 2-glycosyl-benzimidazoles with alpha-d-arabinopyranosyl, beta-d-galactopyranosyl, beta-d-glucopyranosyl, beta-d-mannopyranosyl, and beta-l-rhamnopyranosyl configurations were obtained in 52-73% yields from the corresponding C-glycosylmethanal dimethyl acetals and o-phenylenediamine under catalysis with hydrogen chloride or a strongly acidic cation-exchange resin. Intermediate benzimidazolines were spontaneously oxidized by air to produce the final products in the one-pot procedure. The prepared compounds did not show any inhibitory effect on the growth of 12 strains of five different species of pathogenic yeasts.

Metal tolerance of yeasts isolated from water, soil and plant environments.

The tolerance of seventy yeast strains belonging to 15 species, isolated from water and soil environments as well as from tree leaves, to four heavy metals--copper, zinc, nickel and cadmium were studied. We have found that the interspecific and intraspecific variations in metal tolerance among studied strains were considerable. The highest interspecific variations were observed toward copper and cadmium. The strains of the species Sporobolomyces salmonicolor, Cryptococcus albidus, Cystofilobasidium capitatum, Saccharomyces cerevisiae, and Candida maltosa belonged to the most sensitive ones. In general ascomycetous yeasts were more tolerant to heavy metals than basidiomycetous ones. The differences among strains that came from various natural sources were also found. The most sensitive yeast population originated from untilled soil whereas the most tolerant population was isolated from tree leaves.

Biotransformation of lignin polymers derived from beech wood pulping by Sporobolomyces roseus isolated from leafy material.

The ability of the yeast, Sporobolomyces roseus, isolated from leafy material, to modify lignin derived from beechwood pulping was examined by FTIR and 13C NMR spectroscopy, which revealed oxidative cleavage of the Calpha-Cbeta linkages between lignin units. Using veratryl alcohol as a model substrate confirmed that Sp. roseus could oxidize veratryl alcohol into veratric acid. This yeast might be suitable for the pretreatment of lignocellulosic materials and/or for biotransformation of technical lignins.

The diversity of yeasts in the agricultural soil.

One hundred and eleven yeast strains were isolated from 60 agricultural soil samples. The samples were taken from four various fields located in the southwest of Slovakia. Cryptococcus laurentii, Candida maltosa, Metschnikowia pulcherrima, and Sporobolomyces salmonicolor were the predominant species in the samples collected from all four types of fields. These species represented 78.4-86.6% of the total yeast counts.The results obtained enabled comparisons to be made between forest and agricultural soil yeast population. We have found out that the yeast population in tilled soils was significantly reduced. The number of yeasts in the tilled soils ranged from 40 to 6.8 x 10(3) CFU/g soil and the average number reached approximately 1.12 x 10(3). This number is more than ten times lower in comparison with the forest soils.

Effects of pesticides on yeasts isolated from agricultural soil.

The effect of six various pesticides on the growth of yeasts isolated from agricultural soil was investigated. Two herbicides (with the effective substances lactofen and metazachlor), two fungicides (with the effective substances fluquinconazole and prochloraz), and two insecticides (with the effective substances cypermethrin + chlorpyrifos and triazamate) were tested. It is evident that there are considerable differences in inhibition effects of studied pesticides. The fungicide with the effective substance prochloraz inhibited the growth of majority of yeast strains. The insecticide triazamate at concentration 0.6 mM restricted or inhibited growth of all tested strains. The strains of the genus Cryptococcus were the most sensitive to pesticides, while the strains of the species Cystofilobasidium capitatum, Debaryomyces occidentalis var. occidentalis, and Trichosporon cutaneum were the most resistant.

Biotransformation of waste lignin products by the soil-inhabiting yeast Trichosporon pullulans.

In this study the biotransformation of lignin by-products of beechwood pulping with a soil-inhabiting yeast strain of Trichosporon pullulans was examined. The structural and molecular changes in the lignin during a cultivation process were determined by 13C NMR spectroscopy and gel permeation chromatography analysis, which confirmed the ability of the yeast strain tested to biodegrade lignin. Enzymatic analysis showed the presence of lignin peroxidase and Mn(II) peroxidase in the culture supernatant. The ligninolytic activity of both enzymes increased under carbon-depleted conditions. This observation is particularly important in the biodegradation of recalcitrant lignins in soil.