Emília Breierová

Biosorption of Cadmium Ions by Different Yeast Species

Toxicity and accumulation of Cd2+ in yeasts were studied in eight different yeast species. The adaptation to toxic concentration of this metal was dependent on the production of extracellular yeast glycoproteins. The highest concentration of Cd2+ ions in the growth medium was tolerated by a Hansenula anomala, strain while the lowest tolerance was found by the strain of species Saccharomyces cerevisiae. Extracellular glycoproteins of Hansenula anomala absorbed nearly 90% of the total content of Cd2+ ions bound by yeast cells, while extracellular glycoproteins of Saccharomyces cerevisiae bound only 6% of the total amount of cadmium. This difference is caused by the variable composition of the saccharide moiety in the extracellular glycoproteins. The composition of extracellular glycoproteins changed during the adaptation of the yeast cells to the presence of Cd2+ ions.

Malassezia pachydermatis: properties and storage.

Summary. Five strains of Malassezia pachydermatis isolated from small animals in Bratislava were subcultured, maintained under sterile paraffin oil and preserved in liquid nitrogen. Morphological and physiological characteristics as well as the analysis of long chain fatty acids of the cell mass were determined. The results showed that the maintenance in liquid nitrogen is the most satisfactory method of preservation of pure cultures of Malassezia pachydermatis.

Cryoprotective effects of yeast extracellular polysaccharides and glycoproteins

Eighteen yeast strains were tested for their ability to survive the freeze-thaw process while being cryoprotected. Cryoprotection was accomplished by combining penetrating and nonpenetrating cryoagents. Four nonpenetrating (two extracellular polysaccharides of yeast and two extracellular glycoproteins of yeast) and two penetrating agents were used together with the nutritive-rich medium. Eight different mixtures were tested. The highest survival rate was obtained with glycoproteins of Rhodosporidium toruloides together with DMSO and nutritive-rich medium.

Enhanced antioxidant formula based on a selenium-supplemented carotenoid-producing yeast biomass.

Carotenoid‐producing yeast species such as Rhodotorula glutinis and Sporobolomyces roseus efficiently accumulated selenium from the growth medium. It was observed that incorporation of selenium into yeast cells during the growth inhibited production of β‐carotenoid and other carotenoid precursors (torularhodin and torulene). The yeasts with high content of the carotenoid pigments and selenium may be used for the preparation of a new type of antioxidant formula that could be directly applied for various human and animal diets. We have demonstrated that such a formula can only be produced by separate processes of the cultivation of red yeasts and a subsequent sorption of selenium into the cells.

Effect of cultivation and storage pH on the production of multiple forms of polygalacturonase by Aspergillus niger

SummaryThe production of multiple forms of extracellular polygalacturonase by Aspergillus niger is directly dependent on the pH of maintenance media. The pH of cultivation medium as well as the carbon-source are only secondary factors with limited influence on this production.

Storage of Candida albicans, C. tropicalis and related species in liquid nitrogen.

Storage in liquid nitrogen of a collection ofC. albicans, C. tropicalis and related species checked by numerical and classical taxonomy is described. Strains stored for 3 years in liquid nitrogen were thawed and their survival was tested. After adaptation and regeneration, their fermentation and assimilation spectra, production of chlamydospores and pseudomycelia, appearance and radial growth rate of giant colonies were investigated and compared with the properties of cultures stored under paraffin oil. It follows from the results obtained that two different media —with an increased content of a nitrogen source and with an increased carbon source content —should be used for the post-heating adaptation and regeneration of yeast cells. In some strains it is useful to store them at 4 °C for additional time intervals in order to increase survival of the cells. The above strains can be successfully stored in liquid nitrogen.

Effect of Salt Stress on the Production and Properties of Extracellular Polysaccharides Produced by Cryptococcus laurentii

The composition, main structural features and molecular properties of exopolysaccharides (EP) produced by Cryptococcus laurentii var. laurentii CCY 17-3-16 under optimal (EPo) and NaCl-stress conditions (EPs) as well as their subfractions isolated by gel chromatography were studied using chemical, FT-IR and NMR spectroscopy methods. The results showed that under stress conditions the yeast produced EP with a lower content of protein and phosphorus. In comparison to EPo, the EPs exhibited a substantially larger proportion of high molecular mass populations. NMR analysis of EPs revealed a higher degree of branching with single xylose side chains of the heteromannan components. The increase of the molecular mass and degree of branching of the macromolecular chains of the heteromannan components might in part be related to the function of EPs to protect the yeast cells from water loss and maintain growth conditions under the salt stress.

Production of Enriched Biomass by Carotenogenic Yeasts - Application of Whole-Cell Yeast Biomass to Production of Pigments and Other Lipid Compounds

Yeasts are easily grown unicellular eukaryotes. They are ubiquitous microorganisms, occuring in soil, fresh and marine water, animals, on plants and also in foods. The environment presents for yeast a source of nutrients and forms space for their growth and metabolism. On the other hand, yeast cells are continuously exposed to a myriad of changes in environmental conditions. These conditions determine the metabolic activity, growth and survival of yeasts. Basic knowledge of the effect of environmental factors on yeast is important for understanding the ecology and biodiversity of yeasts as well as for control the yeast physiology in order to enhance the exploitation of yeasts or to inhibit or stop their harmful and deleterious activity. The overproduction of some metabolites as part of cell stress response can be of interest to the biotechnology. For instance carotenogenic yeasts are well known producers of biotechnologically significant carotenoid pigments astaxanthin, ┚-carotene, torulen, torularhodin and under stress conditions this carotenoid accumulation was reported to be increased. Knowledge of molecular mechanism of the carotenoid production stimulation can then lead to improvement of such biotechnological process. Red yeasts are able to accumulate not only carotenoids, but also ergosterol, unsaturated fatty acids, Coenzyme Q10 and other, which can contribute to the biomass enrichment. The use of this stressed biomass in feed industry could have positive effect not only in animal and fish feeds because of high content of physiologically active substances, but it could influence nutritional value and organoleptic properties of final products for human nutrition. Yeast biomass, mainly in the form of Saccharomyces cerevisiae, represents the largest bulk production of any single-celled microorganism throughout the world. In addition to use of

Production and biochemical characterization of polygalacturonases produced byAureobasidium pullulans from forest soil

The production of individual form of extracellular polygalacturonase byAureobasidium pullulans from forest soil was found to depend on the pH of cultivation medium as well as on the nitrogen source in the precultivation or cultivation medium. Polygalacturonases were purified and characterized. The pH optima of polygalacturonases produced in the first phases of cultivation (24 or 48 h) and after 10 days as well as their molecular masses, isoelectric points, action pattern and ability to cleave polymeric and oligomeric substrates were different. Generally, polygalacturonases with random action pattern (EC 3.2.1.15) were produced only in the first phases of cultivation in acidic medium. The function of these enzymes for A.pullulans in the colonization of plant material rather than in the destruction of plant was hypothesized in physiological conditions. Exopolygalacturonases (EC 3.2.1.67) with terminal action pattern were produced in later phases of growth. Oligogalacturonate hydrolase as well as strongly basic polygalacturonase with unusual action pattern on substrates were found.

Production of extracellular polymers by yeast-like generaDipodascus andDipodascopsis under NaCl stress

Changes in the production and basal characteristics of extracellular polymeric compounds were analyzed in eight yeast-like fungi of the generaDipodascus andDipodascopsis in media with and without the addition of NaCl. In the presence of higher concentration of NaCl (8%) the strains produced extracellular polymers (EP) of relatively lower molar mass. Stress EP contained a higher percentage of glutamic acid, mannose and galactose than normal EP. The production of these compounds is probably part of the adaptation mechanism and extracellular protection against disbalanced growth.