Oxidative stress and antioxidant response in a thermotolerant yeast

Abstract Stress tolerance is a key attribute that must be considered when using yeast cells for industrial applications. High temperature is one factor that can cause stress in yeast. High environmental temperature in particular may exert a natural selection pressure to evolve yeasts into thermotolerant strains. In the present study, three yeasts (Saccharomyces cerevisiae, MC4, and Kluyveromyces marxianus, OFF1 and SLP1) isolated from hot environments were exposed to increased temperatures and were then compared with a laboratory yeast strain. Their resistance to high temperature, oxidative stress, and antioxidant response were evaluated, along with the fatty acid composition of their cell membranes. The SLP1 strain showed a higher specific growth rate, biomass yield, and biomass volumetric productivity while also showing lower duplication time, reactive oxygen species (ROS) production, and lipid peroxidation. In addition, the SLP1 strain demonstrated more catalase activity after temperature was increased, and this strain also showed membranes enriched in saturated fatty acids. It is concluded that the SLP1 yeast strain is a thermotolerant yeast with less oxidative stress and a greater antioxidant response. Therefore, this strain could be used for fermentation at high temperatures.

Hypocholesterolemic effects of Kluyveromyces marxianus M3 isolated from Tibetan mushrooms on diet-induced hypercholesterolemia in rat

To investigate the effects of Kluyveromyces marxianus M3 isolated from Tibetan mushrooms on diet-induced hypercholesterolemia in rats, female Wistar rats were fed a high-cholesterol diet (HCD) for 28 d to generate hyperlipidemic models. Hyperlipidemic rats were assigned to four groups, which were individually treated with three different dosages of K. marxianus M3+HCD or physiological saline+HCD via oral gavage for 28 d. The total cholesterol (TC), triglycerides (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C) levels in the serum and liver of the rats were measured using commercially available enzyme kits. In addition, the liver morphology was also examined using hematoxylin and eosin staining and optical microscopy. According to our results, the serum and liver TC, TG, LDL-C levels and atherogenic index (AI) were significantly decreased in rats orally administered K. marxianus M3 (p <0.01), and the HDL-C levels and anti atherogenic index (AAI) were significantly increased (p <0.01) compared to the control group. Moreover, K. marxianus M3 treatment also reduced the build-up of lipid droplets in the liver and exhibited normal hepatocytes, suggesting a protective effect of K. marxianus M3 in hyperlipidemic rats.

Producao e propriedades de beta-galactosidade de Kluyveromyces fragilis NRRL Y-2415 / Production and properties of the Kluyveromyces fragilis NRRL Y-2415 beta-galactosidase

Permeado de soro de queijo e soro de proteinado por acidificacao podem ser utilizados como meio de crescimento de Kluyveromyces fragilis NRRL Y-2415 para obtencao de beta-galactosidase. A suplementacao destes meios com 0,1//de (NH4)2SO4 e 0,05//de KH2PO4 aumenta as producoes de massa celular seca e beta-galactosidase. A extracao da enzima das celulas de levedura feita por autolise em tampao fosfato e 2//de cloroformio foi mais rapida do que quando se substituiu o cloroformio por 2//de tolueno, sendo a atividade obtida funcao da concentracao celular na suspensao. Esta enzima tem pH otimo entre 6,6 e 6,8; a sua estabilidade com respeito a pH de pre-incubacao por uma hora e baixa, o que indica que durante o processo de sua obtencao deve-se trabalhar na faixa otima de pH e temperaturas baixas. Quanto a temperatura de atividade maxima, nao ha diferenca em trabalhar a 30 graus centigrados e a 37 graus centigrados; a 50 graus centigrados a enzima e totalmente inativada. Uma alternativa para pre-purificar esta enzima e utilizar membranas. Usando membrana de 0,08 micro, foi possivel obter o extrato enzimatico livre de fragmentos celulares; com outra de 15.000 Daltons, foi possivel aumentar sua concentracao, obtendo-se no final extrato com 2.500 unidade internacionais de ortonitrofenil beta-D-galactopiranosideo por mL