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PubMed1997

Biodiversity of yeasts from Illinois maize.

Microflora in wound sites of preharvest maize (including bacteria, yeasts, and filamentous fungi) may play a role in attracting insects to maize plants and may also interact with growth and mycotoxin production by filamentous fungi. As little data are available about the yeasts occurring on maize from the U.S. corn belt, samples of milled maize from experimental plantings at the University of Illinois River Valley Sand Field were analyzed. Yeast counts showed slight yearly fluctuation and varied between 3.60 and 5.88 (log cfu/g maize). The majority of the yeasts were Candida guilliermondii (approximately 55%), Candida zeylanoides (24%), Candida shehatae (11%), and Debaryomyces hansenii (3%). Also present were Trichosporon cutaneum, Cryptococcus albidus var. aerius, and Pichia membranifaciens. The occurrence of killer yeasts was also evaluated. Killer yeasts were detected in maize for the first time and were identified as Trichosporon cutaneum and Candid zeylanoides. These were able to kill some representative yeasts isolated from maize, including Candida guilliermondii, Candida shehatae, and Cryptococcus albidus var. aerius. Other maize yeasts (Candida zeylanoides, Debaryomyces hansenii, Pichia membranifaciens) were not affected. The majority of yeasts found on maize were unable to ferment its major sugars, i.e., sucrose and maltose. Some (e.g., Candida zeylanoides) were not even able to assimilate these sugars. The importance of these properties in relation to insect attraction to preharvest ears of maize is discussed.

Yeasts↗
PubMed1993

Salivary yeasts, saliva, and oral mucosa in the elderly.

Yeasts are commensals in the oral cavity and may not cause disease unless there are predisposing host factors, such as other disease, or when medication is being taken. The elderly are at increased risk of yeast infection. In this paper, prevalence of salivary yeasts in a group of 368 inhabitants of Helsinki aged 76, 81, and 86 years is reported. Salivary yeasts were counted by the Oricult-N dip-slide method, salivary secretion rate and buffering capacity were measured, type of dentition was noted, and signs of yeast infection and the occurrence of subjective symptoms were determined. There was no growth of yeasts in 25% of the subjects. From one to 20 colonies/slide were observed in 21%, 21-50 colonies in 21%, and over 50 colonies (a high count) in 33%. Subjects with low salivary flow rates and low buffering capacities had significantly higher yeast counts than did subjects with normal salivary flow rates and buffering capacities. High yeast counts were found in 19% of subjects with natural teeth. The corresponding percentages in those wearing partial or complete dentures were 32 and 41, respectively. High salivary yeast counts were associated with oral mucosal lesions but not with subjective complaints of oral symptoms.

Aged↗
PubMed2000

Performance of yeast-baited traps with Triatoma sordida, Triatoma brasiliensis, Triatoma pseudomaculata, and Panstrongylus megistus in laboratory assays.

The effectiveness of a trap for triatomines baited with yeast cultures has been previously demonstrated for Triatoma infestans in laboratory assays. We report here results from laboratory assays testing yeast traps for Triatoma sordida, Triatoma brasiliensis, Triatoma pseudomaculata, and Panstrongylus megistus. All assays were conducted in an open experimental arena 100 cm x 100 cm, with two traps placed at opposite sides of the arena. One of the traps contained a yeast culture, and the other trap contained a saccharose solution as a control. Two series of experiments were done, one without a refuge for the insects and one with a refuge. The results obtained clearly demonstrated that the yeast-baited traps were effective in the laboratory in capturing both T. sordida and P. megistus. For T. sordida, yeast-baited traps captured significantly more bugs than did the control traps (t test P value = 0.03). For P. megistus, when a refuge was provided during the assay, yeast-baited traps also captured significantly more bugs than did the control traps (t test P value = 0.006). In the experiments with T. brasiliensis and T. pseudomaculata, both traps captured some insects, but the yeast traps captured many fewer bugs than was true with the T. sordida and P. megistus bugs. These results indicate that, in the laboratory, yeast traps can capture considerable numbers of T. sordida and P. megistus in one night. We discuss the potential use of yeast traps for detecting and capturing both triatomine species.

Animals↗
PubMed1988

Influence of addition of yeast culture supplement to diets of lactating cows on ruminal fermentation and microbial populations.

Six ruminally fistulated Holstein cows were utilized in a randomized block design to examine effects of yeast culture supplement on ruminal metabolism and apparent digestibility. Cows were fed a diet of 40% corn silage and 60% concentrate (DM basis). Treatments were control (supplement without yeast cells) and yeast culture supplement. Treatment periods were 6 wk. Ruminal pH, ammonia, molar proportions of acetate and isovalerate, and acetate: propionate ratio were lower and molar proportions of propionate and valerate higher in cows receiving yeast. The concentration of anaerobic bacteria tended to be higher and cellulolytic bacteria concentrations were greater in cows fed yeast than in cows receiving control diet. Supplemental yeast did not affect molar proportions of isobutyrate or butyrate, total VFA, or viable yeast concentrations in ruminal fluid. Ruminal liquid dilution rate and total tract apparent digestibilities were not different between treatments. Rate of disappearance of cellulose in vitro was lower in cows receiving yeast. Less variation in ammonia concentrations and microbial numbers suggest that ruminal fermentation was more stable in cows receiving yeast culture supplement.

Animals↗
PubMed2004

Survey of yeasts for antagonistic activity against Salmonella Poona in cantaloupe juice and wounds in rinds coinfected with phytopathogenic molds.

Application of yeasts as biocontrol agents to prevent mold decay of fruits and vegetables has been described. We examined 10 yeasts for potential antagonistic activity against survival and growth of Salmonella Poona in cantaloupe juice and decay by Cladosporium cladosporioides and Geotrichum candidum in wounds on cantaloupe rind. Cantaloupe juice was inoculated using five schemes: Salmonella Poona only (1.10 log CFU/ml), high (3.93 to 5.21 log CFU/ml) or low populations (1.79 to 3.26 log CFU/ml) of yeasts only, and Salmonella Poona combined with high or low populations of yeasts. High initial populations of Debaryomyces hansenii, Pichia guilliermondii, and Pseudozyma sp. were antagonistic to Salmonella Poona in cantaloupe juice stored at 20 degrees C for 48 h. Wounds in cantaloupe rinds were inoculated with yeast and mold or yeast, mold, and Salmonella Poona, and cantaloupes were stored at 4 degrees C for 14 days or 20 degrees C for 7 days. The pH of rind tissue inoculated with C. cladosporioides and yeasts increased significantly (P < or = 0.05) at 20 degrees C. Wounds that were inoculated with P. guilliermondii, together with C. cladosporioides or G. candidum, did not show mold growth at 4 and 20 degrees C. Populations of Salmonella Poona (6.40, 7.26, and 7.98 log CFU per sample) were lower in wounds coinoculated with G. candidum and three of the test yeasts (D. hansenii, P. guilliermondii, and Cryptococcus albidus, respectively) compared to coinoculation with G. candidum or the other seven yeasts. Candida oleophila and Rhodotorula glutinis showed the most promise in reducing the population of Salmonella Poona in wounds in rinds of cantaloupes coinoculated with G. candidum and stored at 4 degrees C.

Colony Count, Microbial↗
PubMed2004

Distinct immunologic properties of Penicillium marneffei yeasts obtained from different in vitro growth conditions.

A dimorphic fungus Penicillium marneffei is a causative agent of penicilliosis, a life-threatening disseminated disease in immunocompromised hosts predominantly found in southeast Asia and southern China. P. marneffei is the only known Penicillium that possesses a dimorphic characteristic. Since it is difficult to produce large amount of P. marneffei yeasts in vivo for experimentation purpose, yeast cells were produced in different in vitro conditions as alternatives. We interested in investigating the immunologic properties of yeast cells from different culture preparations. It was found that yeast cells obtained from brain heart infusion broth and Sabouraud dextrose broth did not resemble those resided in clinical specimens. A solution of 1% peptone, on the other hand, could induce a direct conidial transition into fission yeasts. Ability of yeast cells in each preparation to activate macrophages was determined by analyzing surface expression of CD40 and CD86 co-stimulatory molecules after two days of co-cultivation. Every P. marneffei yeast cell preparation demonstrated such ability. However, the ones from Sabouraud dextrose broth seemed to induce less phagocytosis. Additionally, although distinct antigenic profiles and lack of conformity in antigenic expression were observed among yeast cells from different culture conditions, most major immunogenic bands were present when Western analysis was performed using polyclonal antisera from penicilliosis patients. The results of the study raise attention on immunological and biochemical characteristics of P. marneffei yeasts if such preparations are to be used in future laboratory investigations.

Antigens, CD↗
PubMed1999

The development of bactericidal yeast strains by expressing the Pediococcus acidilactici pediocin gene (pedA) in Saccharomyces cerevisiae.

The excessive use of sulphur dioxide and other chemical preservatives in wine, beer and other fermented food and beverage products to prevent the growth of unwanted microbes holds various disadvantages for the quality of the end-products and is confronted by mounting consumer resistance. The objective of this study was to investigate the feasibility of controlling spoilage bacteria during yeast-based fermentations by engineering bactericidal strains of Saccharomyces cerevisiae. To test this novel concept, we have successfully expressed a bacteriocin gene in yeast. The pediocin operon of Pediococcus acidilactici PAC1.0 consists of four clustered genes, namely pedA (encoding a 62 amino acid precursor of the PA-1 pediocin), pedB (encoding an immunity factor), pedC (encoding a PA-1 transport protein) and pedD (encoding a protein involved in the transport and processing of PA-1). The pedA gene was inserted into a yeast expression/secretion cassette and introduced as a multicopy episomal plasmid into a laboratory strain (Y294) of S. cerevisiae. Northern blot analysis confirmed that the pedA structural gene in this construct (ADH1P-MFa1S-pedA-ADH1T, designated PED1), was efficiently expressed under the control of the yeast alcohol dehydrogenase I gene promoter (ADH1P) and terminator (ADH1T). Secretion of the PED1-encoded pediocin PA-1 was directed by the yeast mating pheromone alpha-factor's secretion signal (MFa1S). The presence of biologically active antimicrobial peptides produced by the yeast transformants was indicated by agar diffusion assays against sensitive indicator bacteria (e.g. Listeria monocytogenes B73). Protein analysis indicated the secreted heterologous peptide to be approximately 4.6 kDa, which conforms to the expected size. The heterologous peptide was present at relatively low levels in the yeast supernatant but pediocin activity was readily detected when intact yeast colonies were used in sensitive strain overlays. This study could lead to the development of bactericidal yeast strains where S. cerevisiae starter cultures not only conduct the fermentations in the wine, brewing and baking industries but also act as biological control agents to inhibit the growth of spoilage bacteria.

Bacteriocins↗
PubMed1996

Differential response to UV stress and DNA damage during the yeast replicative life span.

The yeast Saccharomyces cerevisiae is mortal. Before they die, individual yeasts bud repeatedly producing a finite number of progeny, which have the capacity for a full life span. A feature of aging in many species is the waning of resistance to stress. To determine whether this is the case in yeast, we have examined the survival (viability) of age-synchronized populations of yeasts of various ages, spanning youth, midlife, and old age, after irradiation with ultraviolet light (UV). Resistance to UV was biphasic. There was an increase through midlife, followed by a precipitous decline. For comparison, another mutagenic agent, ethyl methanesulfonate (EMS), was tested in the same way. The response was very different. A uniphase decrease in resistance to this DNA-alkylating agent was found with a plateau later in life. The results argue that the increase in resistance to UV with age is an active process and not simply a monotonic age change. RAS2 is among the genes that determine yeast longevity. This gene is preferentially expressed in young cells and has a life span-extending effect on yeasts. One known function of RAS2 is to mount a protective response to irradiation by UV, which occurs independently of DNA damage. The distinction between UV and EMS found here is consistent with the notion that resistance to UV plays a role in yeast longevity in a manner not related to DNA damage. Furthermore, it suggests that RAS2 may participate in this response. We have found that RAS2 expression and UV resistance coincide in middle-aged yeasts bolstering this possibility. These data and the eclipse in activity of several longevity determining genes at midlife in yeasts also raise the possibility that active life maintenance processes function through this period, after which the organism operates on any remaining reserves until death.

DNA Damage↗
PubMed2000

Determination of yeast glycogen content by individual cell spectroscopy using image analysis.

A rapid technique has been developed to determine the glycogen content of yeast on an individual cell basis using a combination of image analysis technology and staining of yeast cells with an I(2):KI solution. Changes in mean cellular glycogen content during alcoholic fermentation have been reported using this technique. The glycogen content of stored brewer's yeast is heterogeneous compared to freshly propagated yeast which have a more uniform distribution of glycogen. Analysis of the distribution of yeast glycogen during fermentation indicates that a fraction of yeast cells do not dissimilate glycogen. Therefore, conventional analysis of the mean glycogen content of yeast used to inoculate fermentations is of limited use, unless information regarding the proportion of cells which utilize glycogen is known. Analysis of the distribution of glycogen within a yeast population can serve as a useful indicator of yeast quality.

Aerobiosis↗
PubMed1989

[15N tracer kinetics of the utilization of yeast nitrogen].

The utilization of nitrogen from 15N-labeled Saccharomyces cerevisiae cells was studied in 6 infants by means of oral pulse labeling, comparing native and heat-treated yeast cells. The 15N dose used was 3 mg/kg. The body weight of the subjects varied between 5500 and 9400 g. The yeast cells were harvested from a culture medium which contained 15N ammonium chloride as the only source of nitrogen. The 15N-enrichment of the cells amounted to 95 atom-%. In the course of 48 h following the administration of the native yeast cells, 11% of the tracer dose were renally excreted. The corresponding value after labeling with heat-treated yeast cells was 17.9%. The cumulative renal excretion of the tracer tended to be faster as compared with pulse labeling of the native yeast cells. A paired comparison with labeled native and heated yeast cells in 3 subjects did not reveal any differences in the retention rate of 15N. When untreated 15N yeast cells were administered, 13.2% of the tracer dose were excreted in the urine and 10% respectively in the faeces. The retention was 76.8%. After single pulse labeling with 3 mg 15N/kg from heat-treated yeast cells the corresponding values were 19.4%, 4.4% and 76.2%, respectively. The kinetic of the renal 15N excretion points at the partial absorption of the yeast nitrogen from the colon.

Feces↗
PubMed2000

Antimicrobial and Biological Effects of Bomphos and Phomphos on Bacterial and Yeast Cells.

In this study, the antimicrobial effects of monophosphazenes such as SM, BOMPHOS, and PHOMPHOS were examined on bacterial and yeast strains. In addition, the biological effects of these compounds were tested on the Saccharomyces cerevisiae and Candida albicans cells. The SM has an antimicrobial effect on the bacterial and yeast strains within the range of 100 and 1500 µg. When the concentration was increased, the inhibition zone expanded on the growth media (P < 0.01; P < 0.001). Like SM, BOMPHOS molecule has antimicrobial activity on the bacterial and yeast cells. The most effective concentrations of BOMPHOS on the microorganisms were observed by 1500 µg (P < 0.001). The PHOMPHOS did not effect on the bacterial and yeast cells between 100 and 1000 range, but it has an antimicrobial effect in 1500 µg. In vitro media, the biological effects of these molecules were compared with vitamin E, melatonin, and fish oil on the yeast cells. In S. cerevisiae growth media, the cell densities were increased SM, BOMPHOS, and PHOMPHOS after 20, 30, and 45 h. The highest increase in the cell density were observed in media of BOMPHOS. In C. albicans growth media, the cell density was increased by melatonin after 20, 30, and 45 h, but were decreased by other supplemental groups. Lipid level of S. cerevisiae was reduced by administered 300 and 1000 µg vitamin E and fish oil (P < 0.01). In addition, the lipid level of the same yeast cell were diminished by the 1000 µg melatonin and 300 µg PHOMPHOS (P < 0.05, P < 0.01). The lipid level of C. albicans were increased by vitamin E and BOMPHOS and fish oil, but was decreased with PHOMPHOS (P < 0.01). In conclusion, while high concentration of PHOMPHOS has antimicrobial effects on the bacterial and yeast cells, the SM and BOMPHOS have antimicrobial effects in all the concentrations. PHOMPHOS decreased the lipid level of C. albicans, but BOMPHOS increased in the the same yeast cell. In addition, the antioxidants such as vitamin E, melatonin, and fish oils have affected on the lipid synthesis of yeast cells. Copyright 2000 Academic Press.

Journal Article↗
PubMed1996

Inhibition of yeast-to-mycelium conversion of Candida albicans by conjugated styryl ketones.

Candida albicans is a dimorphic pathogenic yeast capable of producing alternate morphological forms (yeast or mycelium) in response to environmental changes. The dimorphism of C. albicans plays an important role in the pathophysiology of this organism. The intracellular level of glutathione, which helps to maintain the oxidation-reduction potential of the cell, is decreased significantly during the yeast-to-mycelium conversion implicating the possible involvement of thiols in the yeast-to-mycelium transition. To evaluate the possible participation of sulphydryl group(s) containing component(s) in the yeast-to-mycelium transition of C. albicans, we examined the effect of a group of newly synthesized thiol-alkylators on the production of germ tubes from yeast cells. Several conjugated styryl ketones which are thiol-alkylators, and p-chloromercuriphenylsulphonate (a known nonpenetrating thiol-blocker) inhibited the yeast-to-mycelium conversion of C. albicans. The thiol-alkylators at 20 microM failed to inhibit four key enzymes (gamma-glutamyltranspeptidase, glutathione reductase, glutathione S-transferase and glutathione peroxidase) involved in glutathione utilization indicating that the inhibition of yeast-to-mycelium conversion is not mediated by the inhibition of glutathione metabolic enzymes. Moreover, these results suggest that a key thiol-blocker sensitive component(s) containing a critical sulphydryl group(s) is involved in the yeast-to-mycelium transition of C. albicans.

4-Chloromercuribenzenesulfonate↗
PubMed2006

Human dendritic cell interactions with whole recombinant yeast: implications for HIV-1 vaccine development.

Defects in number and function of dendritic cells (DCs) have been observed during HIV-1 infection, so therapeutic HIV-1 vaccine approaches that target or activate DCs may improve vaccine immunogenicity. To determine the potential of recombinant Saccharomyces cerevisiae yeast as an HIV-1 vaccine, we investigated interactions between yeast and human DCs. Yeast induced direct phenotypic maturation of monocyte-derived DCs (MDDCs) and enriched blood myeloid DCs (mDCs), but only indirectly matured blood plasmacytoid DCs (pDCs). Yeast-pulsed MDDCs and blood mDCs produced inflammatory cytokines and stimulated strong allo-reactive T cell proliferation. Both blood DC subsets internalized yeast, and when pulsed with yeast recombinant for HIV-1 Gag protein, both stimulated in vitro expansion of Gag-specific CD8+ memory T cells. These results suggest that S. cerevisiae yeast have potent adjuvant effects on human DCs. Furthermore, recombinant yeast-derived antigens are processed by human blood DCs for MHC class-I cross-presentation. These DC-targeting characteristics of yeast suggest that it may be an effective vaccine vector for induction of HIV-1-specific cellular immune responses.

AIDS Vaccines↗
PubMed1991

[1-14C]oleate-labeled autoclaved yeast: a membranous substrate for measuring phospholipase A2 activity in vitro.

Radiolabeled, autoclaved yeast were tested as a substrate for mammalian phospholipase A2 activity because the only other membranous substrate used for this purpose, autoclaved Escherichia coli, totally lacks a major mammalian phospholipid, phosphatidylcholine. Candida albicans were grown in the presence of [1-14C]oleate and then autoclaved. Sixty three percent of the incorporated label was in yeast phospholipid, and more than 95% of that was in the 2-acyl position. The distribution of label in the yeast phospholipids (phosphatidylcholine and -ethanolamine, -serine + -inositol, and phosphatidic acid corresponded closely to the chemical distribution of phosphorus in those phospholipids. Snake venom (Naja naja) and human synovial fluid phospholipase A2 hydrolyzed yeast phospholipid exclusively to release 14C-labeled fatty acid. When 50-60% of the yeast phospholipid was hydrolyzed, the radioactive fatty acids as determined by gas-liquid chromatographic analysis were predominantly oleate (45%) and linoleate (greater than 54%). Hydrolysis of yeast phospholipid by both enzymes was near-linear with protein and time under conditions of optimal pH (neutral-alkaline) and Ca2- (1-5 mM) previously reported for optimal hydrolysis of autoclaved E. coli phospholipid. N. naja phospholipase A2 showed less preference for phosphatidylethanolamine than -choline as liposomes or yeast phospholipid as compared to human synovial fluid phospholipase A2 which clearly preferred phosphatidylethanolamine to -choline as a liposome or yeast phospholipid. These results illustrate that radiolabeled phospholipids of autoclaved yeast, enriched in phosphatidylcholine, are readily hydrolyzed by snake venom and human nonpancreatic phospholipases A2 and may, therefore, be useful in the measurement of in vitro enzymatic activity.

Animals↗
PubMed1994

Subunit requirements for expression of functional sodium pumps in yeast cells.

Na+/K(+)-ATPase from animal cell membranes is known to consist of an alpha-subunit and a beta-subunit. Amino acids within the alpha-subunit have been shown to participate in the catalytic functions of the enzyme and in the binding of cardioactive steroids. Although the function of the beta-subunit is not known, expression of both alpha- and beta-subunits is required for the functional enzyme. A putative third subunit, the gamma-subunit, has been suggested to be a part of the functional Na+/K(+)-ATPase complex, based on experiments showing that both the catalytic alpha-subunit and a small peptide of M(r) = 11,000 can be labeled by a photoreactive ouabain analog. Although the primary structure for the putative gamma-subunit from rat and sheep was recently deduced from cDNA clones, participation of this small protein in the catalytic activity of the Na+/K(+)-ATPase has not been demonstrated. In experiments described here, the heterologous expression of Na+/K(+)-ATPase in yeast cells was used to investigate whether the gamma-subunit is an essential component of the Na+/K(+)-ATPase. Yeast cells do not contain an endogenous Na+/K(+)-ATPase. The alpha- and beta-subunits or the alpha-, beta- and the putative gamma-subunits of Na+/K(+)-ATPase were expressed in the yeast Saccharomyces cerevisiae and ouabain-sensitive ATPase, p-nitrophenylphosphatase, and 86Rb uptake activities were measured either in membranes prepared from transformed yeast cells, or in intact yeast cells. Nontransformed yeast cells or yeast cells transformed with the gamma-subunit alone served as controls. Northern analysis and Western blots demonstrated that yeast cells do not contain an endogenous peptide with significant sequence homology to the putative gamma-subunit. Yeast samples containing only Na+/K(+)-ATPase alpha and beta subunits were capable of ouabain-inhibitable enzymatic activity and 86Rb transport. No gamma-subunit-dependent differences in the measured enzymatic activities or transport properties were detected in the different samples. These observations establish that the alpha beta-subunit complex is the minimum structural unit required for all the ouabain-sensitive reactions of Na+/K(+)-ATPase.

DNA, Complementary↗
PubMed1995

The highly acidic C-terminal region of the yeast initiation factor subunit 2 alpha (eIF-2 alpha) contains casein kinase phosphorylation sites and is essential for maintaining normal regulation of GCN4.

Regulation of the effective activity of eukaryotic initiation factor 2 (eIF-2) in protein synthesis is known to involve phosphorylation of its alpha subunit. Two mammalian enzymes, the haem-controlled repressor (HCR) and the double-stranded RNA-activated inhibitor (dsI), phosphorylate Ser-51 of the alpha subunit, thereby inhibiting the exchange of bound nucleotides on, and thus the recycling of, eIF-2. In Saccharomyces cerevisiae, the equivalent serine seems to be phosphorylated by the GCN2 protein kinase, which is activated by amino acid starvation. However, in the present paper we show that this is not the only site of phosphorylation in yeast eIF-2 alpha. We report the preparation of recombinant yeast eIF-2 alpha from Escherichia coli and its use in in vitro phosphorylation studies. Mammalian HCR and dsI are shown to phosphorylate specifically Ser-51 of yeast eIF-2 alpha, whereas extracts from yeast cells do not. Instead, at least one of three serine residue in the acidic C-terminal region of this protein is phosphorylated by fractions of yeast possessing casein kinase activities 1 and 2. A triple Ser-->Ala mutant form of yeast eIF-2 alpha was found to be no longer phosphorylated by either of the yeast (or mammalian) casein kinase activities in vitro. Isoelectric focusing of yeast extracts confirmed that the mutated sites normally act as sites of phosphorylation in vivo. The same mutant was used to show that the three sites have no essential function under normal physiological conditions in yeast. In contrast, deletion of the 13 amino acid long C-terminal region of eIF-2 alpha, including the three phosphorylation sites, led to derepression of GCN4 in vivo. Thus removal of the short, highly acidic C-terminal region of eIF-2 alpha has the same regulatory effect on translational (re)initiation as phosphorylation of the Ser-51 residue of the wild-type protein. This result provides new insight into the role of eIF-2 alpha activity in the regulation of translational (re-) initiation.

Amino Acid Sequence↗
PubMed1983

Sedimentation behaviour of aminoacyl-tRNA synthetases from mixed lysates of yeast and rabbit liver.

The subcellular distribution of five aminoacyl-tRNA synthetases from yeast, including lysyl-, arginyl- and methionyl-tRNA synthetases known to exist as high-molecular-weight complexes in lysates from higher eukaryotes, was investigated. To minimize the risks of proteolysis, spheroplasts prepared from exponentially grown yeast cells were lysed in the presence of several proteinase inhibitors, under conditions which preserved the integrity of the proteinase-rich vacuoles. The vacuole-free supernatant was subjected to sucrose density gradient centrifugation. No evidence for multimolecular associations of these enzymes was found. In particular, phenylalanyl-tRNA synthetase activity was not associated with the ribosomes, whereas purified phenylalanyl-tRNA synthetase from sheep liver, added to the yeast lysate prior to centrifugation, was entirely recovered in the ribosomal fraction. A mixture of lysates from yeast and rabbit liver was also subjected to sucrose gradient centrifugation and assayed for methionyl- and arginyl-tRNA synthetase activities, under conditions which allowed discrimination between the enzymes originating from yeast and rabbit. The two enzymes from rabbit liver were found to sediment exclusively as high-molecular-weight complexes, in contrast to the corresponding enzymes from yeast, which displayed sedimentation properties characteristic of free enzymes. The preservation of the complexed forms of mammalian aminoacyl-tRNA synthetases upon mixing of yeast and rabbit liver extracts argues against the possibility that failure to observe complexed forms of these enzymes in yeast was due to uncontrolled proteolysis. Furthermore, this result denies the presence, in the crude extract from liver, of components capable of inducing artefactual aggregation of the yeast aminoacyl-tRNA synthetases, and thus indirectly argues against an artefactual origin of the multienzyme complexes encountered in lysates from mammalian cells.

Amino Acyl-tRNA Synthetases↗
PubMed2006

Lipase production by yeasts from extra virgin olive oil.

Newly produced olive oil has an opalescent appearance due to the presence of solid particles and micro-drops of vegetation water from the fruits. Some of our recent microbiological research has shown that a rich micro-flora is present in the suspended fraction of the freshly produced olive oil capable of improving the quality of the oil through the hydrolysis of the oleuropein. Present research however has, for the first time, demonstrated the presence of lipase-positive yeasts in some samples of extra virgin olive oil which can lower the quality of the oil through the hydrolysis of the triglycerides. The tests performed with yeasts of our collection, previously isolated from olive oil, demonstrated that two lipase-producing yeast strains named Saccharomyces cerevisiae 1525 and Williopsis californica 1639 were able to hydrolyse different specific synthetic substrates represented by p-nitrophenyl stearate, 4-nitrophenyl palmitate, tripalmitin and triolein as well as olive oil triglycerides. The lipase activity in S. cerevisiae 1525 was confined to the whole cells, whereas in W. californica 1639 it was also detected in the extracellular fraction. The enzyme activity in both yeasts was influenced by the ratio of the aqueous to the organic phase reaching its maximum value in S. cerevisiae 1525 when the water added to the olive oil was present in a ratio of 0.25% (v/v), whereas in W. californica 1639 the optimal ratio was 1% (v/v). Furthermore, the free fatty acids of olive oil proved to be good inducers of lipase activity in both yeasts. The microbiological analysis carried out on commercial extra virgin olive oil, produced in four different geographic areas, demonstrated that the presence of lipase-producing yeast varied from zero to 56% of the total yeasts detected, according to the source of oil samples. The discovery of lipase-positive yeasts in some extra virgin olive oils leads us to believe that yeasts are able to contribute in a positive or negative way towards the organological quality of the olive oil.

Candida↗