K. Pavlova

Production of an exopolysaccharide by Antarctic yeast

Psychrophilic Antarctic yeasts produce polysaccharides in different concentrations. According to morphological, cultural, physiological and biochemical characteristics, the best producer strain was identified as Cryptococcus flavus A51. The highest values for viscosity (59.1 mPa s) and crude polysaccharide productivity (5.75 g/L) were obtained in a medium containing 5 % sucrose and 0.25 % (NH4)2SO4, at 24 °C for 6 d. The chemical composition and sugar constituents of the crude exopolysaccharide were determined (92.5 % saccharides, 3.34 % protein, and 4.16 % ash). The monosaccharide composition of the exopolysaccharide obtained from C. flavus strain AL51 was established (55.1 % mannose, 26.1 % glucose, 9.60 % xylose, 1.90 % galactose). The microbial biopolymer has a high molar mass and homogeneity: 82 % of it had M 1.01 MDa.

Production and chemical characterization of an exopolysaccharide synthesized by psychrophilic yeast strain Sporobolomyces salmonicolor AL1 isolated from Livingston Island, Antarctica

The exopolysaccharide (EPS) production by psychrophilic Antarctic yeast Sporobolomyces salmonicolor AL1 reached the maximum yield in medium containing sucrose (50 g/L) and diammonium sulfate (2.5 g/L) after a 5-d fermentation (5.64 g/L) at 22 °C, the dynamic viscosity of the culture broth reaching (after 5 d) 15.4 mPa s. EPS showed a mannan-like structure and high molar mass, and did not affect cellular viability and proliferation of murine macrophages. It exhibited also a protective effect against the toxic activity of Avarol.

Emulsifying power of mannan and glucomannan produced by yeasts

Subject of study was the colloid chemical properties of the biopolymers mannan, synthesized from strain Rhodotorula acheniorum MC, and glucomannan, synthesized from strain Sporobolomyces salmonicolor AL1. Their emulsifying capacity was studied in model systems of aqueous solutions in concentrations from 0.5% to 2.5% with regard to the aqueous phase. Emulsions of the direct type (oil/water) with 50% oil content were obtained. A disperse system with 2.5% glucomannan had 100% intact emulsion in the centrifugation test, while for the system with mannan, this indicator was 72%. Lab cream emulsions were obtained with glucomannan and with the emulsifiers Rofetan N/NS and Arlacel 165 used in the cosmetics industry. It has been established that under standard testing conditions, cream‐like emulsions with 2.0% glucomannan have stability indicators comparable to these of 5.0% rofetan N/NS and 5.0% Arlacel 165. The samples with different concentrations of glucomannan showed a pseudo‐plastic behaviour, as the highest viscosity was shown by the emulsion with 2.0% stored at 45°C. The newly synthesized exopolysaccharides had a distinct emulsifying power and can be applied in the cosmetic and food industries.

Phytase from antarctic yeast strain Cryptococcus laurentii AL27

Cryptococcus laurentii strain AL27 demonstrating significant potential for intracellular phytase production was selected by 2-step screening of Antarctic yeasts. The strain showed increased phytase activity in a culture medium with 40 g/L sucrose, KH2PO4 providing 5 mg/L phosphorus, and cultivation temperature of 24 °C, which relates it to psychrotrophic microorganisms. The enzyme kinetic characteristics according to sodium phytate were Km = 0.98 mmol/L, vlim = 33.3 μmol g−1 min−1. The enzyme had maximum activity at 40 °C and acted within a wide pH range: from 2.0 to 5.5, which is of positive significance for its direct inclusion into the feed of monogastric animals.

Studies of Antarctic yeast for β-glucosidase production

Moss and lichen samples from the region of the Bulgarian base on Livingston Island, Antarctica were examined for the presence of yeasts. Six pure cultures were obtained. They were screened for β-glucosidase production and two of them were selected. These were identified as Cryptococcus albidus AL2 and C. albidus AL3, according to their morphology, reproductive behaviour, and growth at different temperatures, salt concentrations, nutritional characteristics and various biochemical tests. These strains were examined for biosynthesis of β-glucosidase on different carbon sources under aerobic conditions. High exocellular and endocellular activities were obtained when they were grown on cellobiose, methyl-β-D-glucopyranoside and salicin. The time course of growth and β-glucosidase production of the yeast was examined by cultivation in a medium with cellobiose under aerobic conditions at temperatures 18 and 24 °C for 96 h. Cryptococcus albidus AL2 and C. albidus AL3 synthesized exocellular enzyme, respectively 58.33 and 55.83 U/ml and endocellular enzyme 137.75 and 205.34 U/ml at 24 °C for 72 h of the cultivation.

Biomass Production by Antarctic Yeast Strains: An investigation on the Lipid Composition

ABSTRACT Psychrophilic yeast strains Rhodotorula glutinis AL107, Sporobolomyces roseus AL108, Cryptococcus albidus AL55, Cryptococcus laurentii AL56 and Cryptococcus laurentii AL58 isolated from soil sample taken from the region of the Bulgarien base on Livingston Island, Antarctica, were studied. The biomass production was followed after cultivation of the yeasts in a medium with pH 5.3 at 15°C for 120 h. The biomass concentration by psychrophilic yeast strains was: R. glutinis AL107-6.05 g/l, S. roseus AL108-5.78 g/l, Cr. albidus AL55, Cr. laurentii AL56 and Cr. laurentii AL58-6.52 g/l, 6.84 g/l and 6.24 g/l, respectively. The extracted and separated lipids from the samples were supplied to analysis and the compositions of fatty acids, phospholipids, sterols as well as tocopherols were determined. Unsaturated fatty acids, mainly oleic (58.6–63.5%) and of saturated palmitic (18.2–24.5%), predominated in triacylglycerols. Sterols (0.1–0.3%) were valued in the dry yeast biomass. The content of phospholipids, mainly phosphatidylcholine, phosphatidylinositole and phosphatidylethanolamine was found to be in the range of 0.2–1.6%. The quantity of tocopherols was 0–26.3 mg/kg. All of tocopherol classes were established.

Effect of Different Carbon Sources on Biosynthesis of Exopolysaccharide from Antarctic Strain Cryptococcus Laurentii AL62

ABSTRACT Isolate AL62 isolated from Antarctic soil was identified as Cryptococcus laurentii AL62 based on its morphological, cultural and physiological properties and was selected as an active producer of exopolysaccharide. Different carbon sources (pentoses, hexoses and oligosaccharides) were investigated for biosynthesis of biopolymer and sucrose was chosen as the most suitable and available carbon source. The time course of exopolysaccharide synthesis, biomass and pH on different sucrose concentration (30, 40, 50 g/L) were studied. The heteropolysaccharide was composed of the following monosaccharides: xylose, 45.2%; mannose, 33.6%; glucose, 18.4%. It was characterized by polydispersity of the polymer molecule, 60% of it having molecular mass of 8000 Da.

Effect of Different Factors on Biosynthesis of Exopolysaccharide from Antarctic Yeast

ABSTRACT Psychrophilic yeast Isolate 100, was selected as a producer of exopolysaccharide. A laboratory scheme was created for obtaining of the biopolymer. Biotechnological and physicochemical factors influencing its biosynthesis were investigated. It was determined that inocolum quantity from 6–10%, cultivated for 48 hours at 22° C, is suitable for maximum synthesis. The exopolysaccharide that was synthessed in the culture liquid was thermostable at 50°C to 70°C and it degrades at 80°C. The quantity of the sedimentary polymer, that was synthesis on environment with arabinose and mannose from Isolate 100, after incubation in ethanol at 4°C for 120 hours staying at the time of 120 hours in ethanol at 4 °C, was increased with 40%. The influence of the temperature over drying of the exopolysaccharide at 65°C and 105 °C was studied. At the low temperature of drying the polymer contained near 20% humidity. The effect of the experimental conditions (temperature, time, concentration of 2%, 3%, 4%, 5%) on the apparent viscosity values of the cultural liquid was studied. It was found to reveal a behaviour of non-Newtonian liquid. The power law equation of Oswald- de Waale describing the change of the apparent viscosity was derived.

Functional Characteristics of an Exopolysaccharide from Antarctic Yeast Strain Cryptococcus Laurentii AL62

ABSTRACT A heterogeneous exopolysaccharide (EPS) containing having xylose, mannose, and glucose as monosaccharide components was produced by the Antarctic yeast strain Cryptococcus laurentii AL62 with the use of sucrose as a good and reliable carbon source. The water solubility and the surface activity of the biopolymer were studied. The emulsifying and stabilising capacity of oil/water emulsions was evaluated at different concentrations of EPS independently or in combination with plant and microbial polysaccharides (guar gum, cellulose gum, xanthan gum, and Na-alginate). A synergistic effect was shown in relation to the emulsifying and stabilising properties.

Production of Polymers and Other Compounds of Industrial Importance by Cold-Adapted Yeasts

Cold-adapted yeasts from Antarctica, still new and understudied microorganisms, attract considerable interest with their biotechnological potential to synthesise exopolysaccharides (EPS) and other biologically active substances. Yeasts of various genera, species, and strains have been selected as producers of EPS built of residual monosaccharides, the most common ones being mannose and glucose. The physicochemical and rheological properties of the EPS make them suitable for use as emulsifiers and stabilisers in cosmetics. An Antarctic strain produces an EPS with good emulsifying properties; also, its biomass contains biologically active substances that have photoprotective and antioxidant activities. Both products are included in cosmetic compositions designed to enhance the cellular metabolism of the skin and protect it against environmental damage. This chapter reviews the production, characteristics, and application of EPS and metabolites synthesised by cold-adapted Antarctic yeasts.