Induction of flocculation in Pediococcus damnosusby different yeast strains

The induction of flocculation of Pediococcus damnosus by a proteineous factor, purified from the yeast culture supernatant, was strongly dependent on the yeast strain used. The measurement of flocculation inducing activity can be used to examine the affinity of yeast strains toward eventual bacterial contaminants or to evaluate the stability of cocultures in mixed culture fermentations.     

Effect of vitamin A treatment on superoxide dismutase-deficient yeast strains

Vitamin A (Vit A) is widely suggested to be protective against oxidative stress. However, different studies have been demonstrated the pro-oxidant effects of retinoids in several experimental models. In this work, we used the yeast Saccharomyces cerevisiae as a model organism to study the Vit A effects on superoxide dismutase (SOD)-deficient yeast strains. We report here that Vit A (10, 20 and 40 mg/ml) decreases the survival of exponentially growing yeast cells, especially in strains deficient in CuZnSOD (sod1Δ) and CuZnSOD/MnSOD (sod1Δsod2Δ). We also observed the protective effect of vitamin E against the Vit A-induced toxicity. Possible adaptation effects induced by sub-lethal oxidative stress were monitored by pre-, co- and post-treatment with the oxidative agent paraquat. The enzymatic activities of catalase (CAT) and glutathione peroxidase (GPx), and the total glutathione content were determined after Vit A treatment. Our results showed that CuZnSOD represents an important defence against Vit A-generated oxidative damage. In SOD-deficient strains, the main defence against Vit A-produced reactive oxygen species (ROS) is GPx. However, the induction of GPx activity is not sufficient to prevent the Vit A-induced cell death in these mutants in exponential phase growth.     

Regioselective hydrolysis of acetates in the presence of different yeast strains

The model compound, hexane-1,2-diol diacetate, was hydrolyzed in the presence of supernatant obtained after cultivation of 4 yeast strains: Pichia jadinii, Rhodotorula glutinis and Yarrowia lipolytica KKP 379 and Saccharomyces cerevisiae 102 to evaluate the type of catalysis. The regioselectivity of extracellular enzymes as a function of hydrolysis towards primary and secondary acetic acid ester groups was monitored. The enzymes secreted by P. jadinii, R. glutinis and Y. lipolytica KKP 379 exhibited high regioselectivity towards primary position, while those from S. cerevisiae showed practically no discrimination between the ester groups.     

Investigation of different yeast strains for the detoxification of ochratoxin A

High concentrations of ochratoxin A (OTA) in feed lead to growth depression in animals. It has been reported that binders can be used for deactivating aflatoxins but not for other mycotoxins without negatively influencing the animals health. In this study a strain from the genus ofTrichosporon with the ability to cleave ochratoxin A very selectively into phenylalanine and the non-toxic ochratoxin α (OTα) could be isolated. This strain was selected from a pool of OTA detoxifying microorganism by carrying out several investigations.Trichosporon sp. nov. can be fermented and stabilized. In a feeding trial with broilers lyophilizedTrichosporon-cells could compensate performance losses caused by OTA. Presented at the 25^th Mykotoxin Workshop in Giessen, Germany, May 19–21, 2003     

The effect of caffeine on survival of UV-irradiated diploid yeast strains of different sensitivities

The action of caffeine post-treatment after UV exposure in three strains of diploid yeast has been studied. The addition of the drug to the plating medium reduced survival in all cases. Higher colony-forming abilities were found in all strains when the UV dose had been split into two fractions with an interval of about 6 h. Caffeine added to the incubation medium between dose fractions did not interfere with this process in the wild type but suppressed split-dose sparing completely in two sensitive strans.     

Xylitol production from rice straw hemicellulose hydrolysate using different yeast strains

Thirty different yeast strains belonging to four different genera (Candida, Debaryomyces, Hansenula and Pichia) were evaluated for xylitol production in rice straw hemicellulose hydrolysate under two aeration levels. Candida guillier-mondii FTI-20037, C. mogii NRRL Y-17032, C. parapsilosis IZ-1710 and C. veronae IZ-945 produced xylitol from rice straw hemicellulose hydrolysate with high yields (>60%). The best performance was by C. mogii, which yielded 0.65 g xylitol/g at 0.40 g/l.h over 75 h. This revised version was published online in November 2006 with corrections to the Cover Date.     

DNA alkylation by mustard gas in yeast strains of different repair capacity

Reaction of the toxic and mutagenic alkylating agent mustard gas with DNA of the yeast Saccharomyces cerevisiae was analyzed qualitatively and quantitatively. Within the dose range tested (2 X 10(-5)-2 X 10(-3) M) DNA in vivo is alkylated dose-proportionally. DNA alkylation and relative distribution of purine derivatives are not influenced by the cell's sensitivity towards the mutagen. At LD37 (4.4 X 10(-4) M) the wild type contains 44 300 purine derivatives: 9200 3-alkyladenines (20%), 29600 7-alkylguanines (67%) and 5500 diguaninyl derivates (13%) per genome. In sensitive strains the number of derivates per genome at LD37 is reduced according to the dose reduction factor. Alkylation at the position O6 of guanine by mustard gas cannot be shown, the method's limit of detection being 0.3% amongst purine derivates.     

The oxygen effect in haploid and diploid yeast strains of different sensitivities

The extent of the oxygen effect for cell survival was studied in diploid and haploid wild-type yeast and in mutants beloning to the rad2, rad6 and rad50 epistatic group. In haploids, reduced oxygen enhancement ratios were found in rad52, rad6 and rad18. The latter two also showed some influence of the mating type. In diploids the oxygen effect was decreased in rad2, rad52 and rad18.     

不同酿酒酵母(Schromycese cerovisea)对黄酒挥发性香气物质的影响

研究不同酵母菌株对黄酒挥发性香气物质形成的影响,采用4种不同酿酒酵母(黄酒活性干酵母、工业生产用黄酒酵母HJ-1,HJ-2、耐高温活性干酵母(NGW))菌株进行实验室黄酒酿造试验,采用固相微萃取-气质联用技术测定了发酵后四种黄酒中挥发性香气物质含量,检测出与酵母相关的27种挥发性成分.研究结果表明不同酵母菌株酿制黄酒样品挥发性香气物质存在明显的差别.其中,HJ-2菌株β-苯乙醇,总酯含量较高,香气较为纯正;NGW活性干酵母挥发性酸含量较高;黄酒活性干酵母挥发性酯含量较低.本研究发现通过选用不同酵母菌株能够有效的调节黄酒生产风味物质的形成.     

Activity of different ''killer'' yeasts on strains of yeast species undesirable in the food industry

Killer strains of the genera Saccharomyces, Hansenula and Kluyveromyces were tested for killing activity against yeasts that cause trouble in the food industry (in the genera Zygosaccharomyces, Kloeckera, Saccharomycodes and Schizosaccharomyces). Saccharomyces strains killed only Zygosaccharomyces rouxii strains, while non-Saccharomyces strains showed a wider anti-yeast spectrum. The Kluyveromyces phaffii killer strain was of particular interest because of its killer action against Kloeckera apiculata, Saccharomycodes ludwigii and Zygosaccharomyces rouxii.     

Toxicity of mercaptoethanol to mutant strains of the yeast Pichia methanolica growing on different carbon sources

Addition of beta-mercaptoethanol at a concentration of 2-3 mM to media containing methanol, glucose, or yeast extract caused a 50% inhibition of the growth of wild-type yeast Pichia methanolica; mercaptoethanol at a concentration of 0.7 to 25 mM inhibited the growth of the mutant strain ecr1. The mutation mth1 of P. methanolica repressed its ability to consume methanol and was accompanied by the loss of alcohol oxidase (EC 1.1.3.13) activity. beta-Mercaptoethanol restored the ability of mth1 mutant cells to grow on methanol and stimulated their growth under derepression conditions. The growth effect of beta-mercaptoethanol during derepression was accompanied by partial restoration of alcohol oxidase activity.     

甾醇C-22去饱和酶高表达对酵母细胞麦角甾醇合成的影响

通过PCR扩增克隆到酵母菌甾醇C-22去饱和酶基因(ERG5)的编码序列及其终止子序列,以大肠杆菌-酿酒酵母穿梭质粒YEp352为载体,以磷酸甘油酸激酶基因PGK1启动子为上游调控元件构建了酵母菌表达质粒pYPE5。以铜离子螯合蛋白基因CUP1替换ERG5基因内部序列获得ERG5破坏菌株YSE5,其中麦角甾醇的合成被阻断,而积累了甾醇中间体Ergosta-5,7-dien-3β-ol。表达质粒pYPE5转化破坏菌株后使细胞恢复了合成麦角甾醇的能力。说明表达质粒上的ERG5基因得到了功能性的表达。将表达质粒pYPE5转化酿酒酵母单倍体菌株YS58,通过营养缺陷互补筛选到重组菌株YS58(pYPE5)。对重组菌株、破坏菌株和互补菌株细胞甾醇组分和含量进行测定,发现重组菌株和互补菌株的麦角甾醇和总甾醇含量明显低于对照菌YS58(YEp352)。测定不同培养时间细胞的麦角甾醇含量,发现重组菌株的麦角甾醇含量始终低于对照菌YS58(YEp352)。可见,ERG5在酵母中的高表达导致细胞麦角甾醇含量降低。     

The same configuration of Ty elements promotes different types and frequencies of rearrangements in different yeast strains

Summary We examined Ty-mediated genomic rearrangements in three related mitotically dividing haploid yeast strains having the same configuration of Ty elements in the CYC1-sup4 interval of chromosome X. Surprisingly, quite different types and frequencies of rearrangements were found in the three strains. In one strain we found only Ty-mediated deletions, which occurred with a frequency of about 1×10^-6. Another strain yielded similar deletions, but approximately one-third of these were accompanied by adjacent Ty-mediated inversions. A third strain was found to have an extremely high rate of inversion/reinversion between two of the three Ty elements. This rate was conservatively estimated to be 1.4±0.2×10^-2 per cell per generation, which is at least 2 orders of magnitude higher than previously reported values for Ty-mediated rearrangements. These data provide evidence that local regions of the genome can, in some cases, be much more fluid than had been previously believed.     

Effect of ethanol,temperature and pH on the stability of killer yeast strains

The effects of temperature, pH and ethanol on the stability of killer wine yeasts were studied. Laboratory and collection strains as well as the strains prepared by the protoplast-fusion technique were used and a decline of killing activity was observed in the complete medium and in grape juice. The relationship between the loss of killer properties in fusant strains and the stability of the original donor strain was established. The negative effect of the ethanol addition on the killer character of the strains used and the possibilities of its stabilization are discussed.