Absence Of Yeast Research Articles

Food Supplement in Daphnia similis and Ceriodaphnia dubia Cultures: Effects of Yeast and Feed Digestion

Over ten years the diet consisting of green algae (Pseudokirchneriella subcapitata) and a suspension of digested fish flake food plus yeast was employed in culturing daphnids, Daphnia similis and Ceriodaphnia dubia in the Aquatic Ecotoxicology Laboratory of CETESB (Companhia Ambiental do Estado de São Paulo, SP, Brazil). However, oscillations in the quality of cultures, with adverse effects on adult survival, were attributed to the addition of this complement. For this reason, experiments were conducted to evaluate the supplying of such mixture with the presence and absence of yeast and, later on, with and without digestion of fish flake food. The results showed that a diet including algae and the suspension of non digested (solubilized) fish flake food, permitted the attainment of the quality criteria for Daphnia similis and Ceriodaphnia dubia cultures, established in the respective standard procedures.

Effects of chemical additives and ensiling time on whole plant wheat silage microbial profiles inferred by phenotypic and 16S ribosomal DNA analyses

The objectives of this study were to test the effects of various chemical additives, and ensiling time periods on microbial profiles of whole plant wheat silage (WPWS). WPWS was harvested at dough maturation stage, and ensiled with sodium chloride (T), sodium bicarbonate (N), sucrose (S), or urea (U) at 1% dry matter (DM) (w/w). Each WPWS treatment (i.e. T, N, S, and U) was ensiled in 1dm(3) duplicate anaerobic jars for 7, 14, 28, 35, 42, 49, and 56days. The highest lactic acid concentration was detected for U (5.9% DM) compared to the control (0.5% DM) at day 56. Similarly, the highest ammonia concentration was observed for U (9.3% DM) compared to the control; T, N, and S treatments averaged 2.4% DM. A higher lactic acid bacteria (LAB) count was observed between days 14 and 56 for all treatments relative to control WPWS, which averaged 6.7 and 5.6 c.f.u./g of fresh material, respectively. The highest quality silage was observed for N and U treated WPWS, with an absence of yeasts and molds from days 7 to 49. Identification of bacterial isolates at days 7 and 56 from each individual silage treatment was performed based on phenotypic (biochemical tests), and molecular (16S rDNA partial gene sequence) methods. 16S rDNA sequence results identified U7 and N56 isolates as Enterococcus faecium, and demonstrated positive galactose, ribose, lactose, maltose, mannitol, mannose, sucrose, and trehalose fermenting characteristics. In addition, most isolates exhibited growth potential in 6.5% NaCl. Overall sequence alignment results supported phenotypic identification, and indicated that U and N treated WPWS were LAB (Enterococcus) dominant compared to the control (non-LAB).

Rationalizing translation attenuation in the network architecture of the unfolded protein response

Increased levels of unfolded proteins in the endoplasmic reticulum (ER) of all eukaryotes trigger the unfolded protein response (UPR). Lower eukaryotes solely use an ancient UPR mechanism, whereby they up-regulate ER-resident chaperones and other enzymatic activities to augment protein folding and enhance degradation of misfolded proteins. Metazoans have evolved an additional mechanism through which they attenuate translation of secretory pathway proteins by activating the ER protein kinase PERK. In mammalian professional secretory cells such as insulin-producing pancreatic beta-cells, PERK is highly abundant and crucial for proper functioning of the secretory pathway. Through a modeling approach, we propose explanations for why a translation attenuation (TA) mechanism may be critical for beta-cells, but is less important in nonsecretory cells and unnecessary in lower eukaryotes such as yeast. We compared the performance of a model UPR, both with and without a TA mechanism, by monitoring 2 variables: (i) the maximal increase in ER unfolded proteins during a response, and (ii) the accumulation of chaperones between 2 consecutive pulses of stress. We found that a TA mechanism is important for minimizing these 2 variables when the ER is repeatedly subjected to transient unfolded protein stresses and when it sustains a large flux of secretory pathway proteins which are both conditions encountered physiologically by pancreatic beta-cells. Low expression of PERK in nonsecretory cells, and its absence in yeast, can be rationalized by lower trafficking of secretory proteins through their ERs.

Archaeal Pus10 proteins can produce both pseudouridine 54 and 55 in tRNA

Pus10, a recently identified pseudouridine (Psi) synthase, does not belong to any of the five commonly identified families of Psi synthases. Pyrococcus furiosus Pus10 has been shown to produce Psi55 in tRNAs. However, in vitro studies have identified another mechanism for tRNA Psi55 production in Archaea, which uses Cbf5 and other core proteins of the H/ACA ribonucleoprotein complex, in a guide RNA-independent manner. Pus10 homologs have been observed in nearly all sequenced archaeal genomes and in some higher eukaryotes, but not in yeast and bacteria. This coincides with the presence of Psi54 in the tRNAs of Archaea and higher eukaryotes and its absence in yeast and bacteria. No tRNA Psi54 synthase has been reported so far. Here, using recombinant Methanocaldococcus jannaschii and P. furiosus Pus10, we show that these proteins can function as synthase for both tRNA Psi54 and Psi55. The two modifications seem to occur independently. Salt concentration dependent variations in these activities of both proteins are observed. The Psi54 synthase activity of M. jannaschii protein is robust, while the same activity of P. furiosus protein is weak. Probable reasons for these differences are discussed. Furthermore, unlike bacterial TruB and yeast Pus4, archaeal Pus10 does not require a U54 x A58 reverse Hoogstein base pair and pyrimidine at position 56 to convert tRNA U55 to Psi55. The homology of eukaryal Pus10 with archaeal Pus10 suggests that the former may also have a tRNA Psi54 synthase activity.

L(+)-Lactic acid production from starch by a novel amylolytic Lactococcus lactis subsp. lactis B84

A new Lactococcus lactis subsp. lactis B84, capable of utilizing starch as a sole carbon source and producing l(+)-lactate, was isolated from spontaneously fermented rye sourdough. Aiming at maximum lactic acid productivity, the components of the media and the cultivation conditions were varied. In MRS-starch medium (with absence of yeast and meat extracts), at 33 °C, agitation 200 rpm and pH 6.0 for 6 days complete starch hydrolysis occurred and 5.5 g l −1 lactic acid were produced from 18 g l −1 starch. The identification of strain B84 was based on genetic criteria. Amplified ribosomal DNA restriction analysis (ARDRA), PCR with species-specific primers and sequencing of the 16S rDNA proved its species affiliation. Four genes for enzymes, involved in starch degradation were detected in B84 genome: amyL, amyY, glgP and apu, coding cytoplasmic and extracellular α-amylases, glycogen phosphorylase and amylopullulanase, respectively. Reverse transcription PCR experiments showed that both genes, encoding α-amylases ( amyL and amyY) were expressed into mRNAs, whereas apu and glgP were not. Amylase activity assay was performed at different pH and temperatures. The cell-bond amylase proved to be the key enzyme, involved in the starch hydrolysis with maximum activity at 45 °C and pH 5.4.

Denture‐related stomatitis: identification of aetiological and predisposing factors – a large cohort

The aim of this study was to identify and characterize aetiological and predisposing factors in denture-related stomatitis (DRS), by means of a case-control, transversal study, in a large cohort of 140 persons wearing removable maxillary polymethylamethacrylate prostheses. Data were obtained by (1) a questionnaire that included the identification of the subject, demographic and social data, medical history and behaviour; (2) intra-oral examination; (3) evaluation of the prosthesis; (4) microbiological examination; (5) yeast identification and analyses using Epi-info and the chi-square test. Results showed significant associations between DRS and yeasts, gender, age and alcohol consumption. We also found a significant relationship between the presence of yeasts and hyposalivation and decreased salivary pH. We found a highly significant difference between groups with and without DRS concerning the presence or absence of yeasts, regardless of the sample origin. Most cases of DRS showed the presence of Candida albicans. The results confirm a highly significant difference between groups with and without DRS concerning the presence or absence of yeasts.

Eggs chips prepared by using different millet flours as binders and changes in product quality during storage

Whole liquid egg was homogenized and mixed with optimized quantities of refined wheat flour, rice flour, corn starch, spices, salt and millet flour, viz., pearl millet ( Pennisetum vulgare), barley ( Hordeum vulgare), or sorghum ( Sorghum vulgare). The dough was flattened in to 2–3 mm thick sheet, cut in to 2.5 × 3 cm strips and fried in refined sunflower oil to obtain ready-to-eat egg chips. The cooled chips were packed in metalised polyester bags, sealed with air or nitrogen-gas, and stored at ambient temperature (27 ± 2 °C) for 4 months. Inclusion of barley flour caused lowest fat content (14.9%) and water activity ( a w = 0.38). Decrease in pH (6.3–6.5 to 5.6–6.0), crispiness (11.3–15.4 to 7.8–13.1 N), sensory quality scores (6.8–8.8 to 5.2–7.9) and increase in a w (0.38–0.46 to 0.44–0.55), free fatty acids (FFA) (0.17–0.32 to 0.83–1.76 as % oleic), thiobarbituric acid (TBA) values (0.62–0.75 to 1.46–2.13 mg malonaldehyde/kg) were noticed in fried egg chips during storage at 27 ± 2 °C. Hunter colour values were marginally affected. Low standard plate counts (1.7–2.9 log cfu/g) and spore counts (1.2–1.6 log cfu/g) and absence of yeasts and moulds, colifoms, staphylococci and enterococci throughout the storage period ensured the microbiological safety of egg chips. All the products were sensorily acceptable during storage up to 4 months and barley egg chips, however, were judged superior by the panelists compared to chips containing pearl millet or sorghum flours.

Influence of aerobic and anaerobic conditions and yeasts on the reaction between (+)-catechin and glyoxylic acid

The reaction between (+)-catechin and glyoxylic acid in wine model solutions was studied under aerobic and anaerobic conditions in the presence and absence of yeasts with a view to determine their contributions to browning of white wine. Under aerobic conditions, the presence of yeasts reduced the production of colored products, the formation rate of which was similar to that observed under anaerobic conditions and in the absence of yeasts. These results reveal that yeasts and intermediate reaction products compete for oxygen. In the absence of oxygen, the production of colored compounds was even smaller in presence of yeasts, as a result of their ability to retain browning products as they form. Because the absence of oxygen not inhibited the formation of intermediate products resulting from oxidation reactions, an alternative oxidation pathway are proposed acting the glyoxylic acid as oxidant. In the usual concentrations of catechin in white wines, the studied reaction of (+)-catechin-glyoxylic acid can contribute significantly to the alteration of the wine color.

Microfiltration of whey proteins adsorbed on yeast cells

SummarySoluble whey proteins (WPs), adsorbed on yeast cells, were recovered by a crossflow microfiltration (MF) technique using a cellulose nitrate membrane with a pore size of 0.45 μm. The crossflow velocity was 1.5 m s−1 with a transmembrane pressure of 200 kPa at 25 °C. A series of protein rejections occured at various pH values ranging from 2 to 8. WPs adsorbed more on to yeast cells at low pH (pH < 4) than at high pH values, probably because they were positively charged at low pH. It was also shown that permeate flux increased and Modified Membrane Fouling Index values decreased at low pH levels. When the yeast concentration was 50 g L−1, the flux decreased five times compared with that in the absence of yeast. Protein recovery increased with increasing yeast concentrations. The highest protein recovery was found to be 85% at a yeast concentration of 50 g L−1 at a steady state flux rate of 10−6 m s−1 at 25 °C. When diluted solutions of whey were used, the same rejection of protein, adsorbed on yeast cells, was achieved at ten times lower amounts of yeast cells. This technique not only provides for the recovery of protein but also may give rise to the direct use of yeast cells, which are rich in protein, in the baking industry. WPs absorbed by yeast cells can be used to produce nutritionally rich products in areas where yeasts have been already used.

The mitochondrial protein frataxin prevents nuclear damage.

The mitochondrial protein frataxin helps maintain appropriate iron levels in the mitochondria of yeast and humans. A deficiency of this protein in humans causes Friedreich's ataxia, while its complete absence in yeast (Delta yfh1 mutant) results in loss of mitochondrial DNA, apparently due to radicals generated by excess iron. We found that the absence of frataxin in yeast also leads to nuclear damage, as evidenced by inducibility of a nuclear DNA damage reporter, increased chromosomal instability including recombination and mutation, and greater sensitivity to DNA-damaging agents, as well as slow growth. Addition of a human frataxin mutant did not prevent nuclear damage, although it partially complemented the Delta yfh1 mutant in preventing mitochondrial DNA loss. The effects in Delta yfh1 mutants result from reactive oxygen species (ROS), since (i) Delta yfh1 cells produce more hydrogen peroxide, (ii) the effects are alleviated by a radical scavenger and (iii) the glutathione peroxidase gene prevents an increase in mutation rates. Thus, the frataxin protein is concluded to have a protective role for the nucleus as well as the mitochondria.

Yeast-induced inhibition of (+)-catechin and (-)-epicatechin degradation in model solutions.

(+)-catechin and (-)-epicatechin degradation in water-alcohol solutions containing Fe2+ and tartaric acid was studied in the presence and absence of yeasts. On the basis of the results, yeast partially inhibited the degradation of both flavans, with much slower formation of browning products absorbing at 420 and 520 nm. In comparative terms, yeast was found to be more efficient toward the degradation products of (+)-catechin absorbing at the latter wavelength. Likewise, the presence of yeast decreased the yield of a group of colored compounds eluting at high retention times in HPLC and indicated these as important contributors to color darkening in white wines. This inhibitory effect may in part account for the resistance to browning observed over periods of several years in sherry wines subjected to biological aging under flor yeast.

The bZIP-like motif of hnRNP C directs the nuclear accumulation of pre-mRNA and lethality in yeast

The hnRNP C protein tetramer cooperatively binds 230 nt increments of pre-mRNA in vitro in a salt-resistant manner and is located along the length of vertebrate transcripts in vivo. Based on these and other findings it has been suggested that hnRNP C functions as a chaperonin to maintain long lengths of RNA topologically single-stranded and accessible to splicing factors. We report here that human C protein is lethal when expressed in the yeast Saccharomyces cerevisiae. Through a series of fluorescent immunolocalization studies, lethality was observed to be associated with the rapid nuclear accumulation of both C protein and yeast pre-mRNA. Studies using various protein constructs and the two hybrid assay reveal that these events are dependent on the basic 40 residue high-affinity RNA binding domain and its contiguous leucine zipper-like motif (the bZLM, residues 140-214). Additionally, equilibrium binding studies have shown that the bZLM is the determinant of C protein’s salt-resistant RNA binding mode. Taken together, these findings further distinguish the bZIP-like domain as the major determinant of C protein’s high-affinity interaction with RNA, oligomerization, and its highly cooperative RNA binding activity. Finally, these findings indicate that yeast and vertebrates may possess a conserved mechanism for general import of RNP although a true homolog to vertebrate C protein appears not to exist in yeast. Lethality is likely due to the absence in yeast of specific mechanisms for the removal of human C protein from nascent transcripts.

Phenolic compounds and browning in sherry wines subjected to oxidative and biological aging.

The composition in hydroxybenzoic and hydroxycinnamic acids, hydroxycinnamic esters, tyrosol, syringaldehyde, and flavan-3-ol derivatives of three different types of sherry wine obtained by aging of the same starting wine under different conditions was studied. So-called "fino" wine was obtained by biological aging under flor yeasts, "oloroso" wine by oxidative aging, and "amontillado" wine by a first stage of biological aging followed by a second oxidative step. On the basis of the results, the wines subjected to oxidative aging exhibited higher phenol contents, in addition to scarcely polar compounds absorbing at 420 nm that were absent in the wines obtained by biological aging. Taking into account that flavan-3-ol derivatives play an important role in wine browning, a model catechin solution was inoculated with flor yeast which, contrary to the findings of other authors in the absence of yeasts, formed no colored compounds. This different behavior may account for the resistance to browning of pale sherry wines in the presence of flor yeasts.

Nuclease-hypersensitive Chromatin Formed by a CpG Island in Human DNA Cloned as an Artificial Chromosome in Yeast

CpG islands are mostly unmethylated GC-, and CpG-rich chromosomal segments overlapping promoter sequences in all housekeeping and many tissue-specific genes in vertebrates. Typically, these islands show an open chromatin structure, low in histone H1 and rich in acetylated histones. We have previously found that the island-like CGCG-rich sites in human DNA are hypersensitive to DNase I upon cloning in Saccharomyces cerevisiae. Here we studied, with a higher resolution, the chromatin formed in yeast by one such site, the CpG island accompanying the human glucose-6-phosphate dehydrogenase gene. We have found two strong hypersensitive sites and several positioned nucleosomes flanking the island despite the absence in yeast of such chromatin fiber-shaping factors as histone H1, methyltransferase, and the tissue-specific transcription factors. This finding, together with similar observations from our laboratories and others supports the idea that variations in GC and/or CpG content substantially contribute to the DNA sequence features modulating the structure of the chromatin. The composition-dependent fluctuations in the accessibility of DNA in the chromatin may constitute an evolutionary advantage and may explain the surprising compositional selection that acts in both the coding and non-coding segments of some genes during mammalian evolution.

Use of virginiamycin to control the growth of lactic acid bacteria during alcohol fermentation.

The antibiotic virginiamycin was investigated for its effects on growth and lactic acid production by seven strains of lactobacilli during the alcoholic fermentation of wheat mash by yeast. The lowest concentration of virginiamycin tested (0.5 mg Lactrol kg-1 mash), was effective against most of the lactic acid bacteria under study, but Lactobacillus plantarum was not significantly inhibited at this concentration. The use of virginiamycin prevented or reduced potential yield losses of up to 11% of the produced ethanol due to the growth and metabolism of lactobacilli. However, when the same concentration of virginiamycin was added to mash not inoculated with yeast, Lactobacillus rhamnosus and L. paracasei grew after an extensive lag of 48 h and L. plantarum grew after a similar lag even in the presence of 2 mg virginiamycin kg-1 mash. Results showed a variation in sensitivity to virginiamycin between the different strains tested and also a possible reduction in effectiveness of virginiamycin over prolonged incubation in wheat mash, especially in the absence of yeast.

In vitro H2 utilization by a ruminal acetogenic bacterium cultivated alone or in association with an archaea methanogen is stimulated by a probiotic strain of Saccharomyces cerevisiae.

The effects of a live strain of Saccharomyces cerevisiae on hydrogen utilization and acetate and methane production by two hydrogenotrophic ruminal microorganisms, an acetogenic bacterial strain and an archaea methanogen, were investigated. The addition of yeast cells enhanced by more than fivefold the hydrogenotrophic metabolism of the acetogenic strain and its acetate production. In the absence of yeasts, and in a coculture of the acetogen and the methanogen, hydrogen was principally used for methane synthesis, but the presence of live yeast cells stimulated the utilization of hydrogen by the acetogenic strain and enhanced acetogenesis.

Effects of formulation and processing conditions on easily extractable lipid and nitrogen components of wheat sourdoughs

SummaryThe changes in free lipid (neutral lipids, glycolipids, and phospholipids) and extractable nitrogen (amino acids, peptides, and proteins) components of unyeasted and yeasted wheat sourdoughs started with Lactobacillus plantarum B‐39 were investigated in samples under different processing conditions. A central composite surface response design was used with factor analysis to investigate the effect of flour extraction rate (ash content), added water, presence or absence of yeast, and fermentation temperature on readily extractable lipid and nitrogen components. Absolute values for extractable protein and non‐protein components were highly correlated with ash content of flour (factor 1); whereas phospholipids and neutral lipids were closely connected with added water (factor 2). Sixty sourdoughs were classified into three groups: 1) high‐ash fermented sourdoughs produced high (>350 mg kg−1) total non‐protein amino nitrogen and medium (<3 mg g−1) lipid levels; mid‐ash flour doughs had lower levels of both components; 2) low‐ash fermented sourdoughs produced low (<300 mg kg−1) levels of amino acids and peptides and medium lipids levels, and 3) unfermented sourdoughs had low (<250 mg kg−1) levels of non‐protein nitrogen components and most made with lowash flour had medium lipid levels; most made with medium and high‐ash flours had high (>4 mg g−1) neutral lipid levels and were largely separated from the low‐ash group. The most promising sourdoughs for bread were those with low added water, fermented from higher ash flour with maximum levels of extractable amino acids, peptides and proteins and medium to high polar and neutral lipid levels.

The presence of tRNA pseudogenes in mammalia and plants and their absence in yeast may account for different specificities of pre-tRNA processing enzymes

Six of 13 cloned members of the human tRNA Val gene family code for tRNA Val pseudogenes, of which all but one are transcribed efficiently in HeLa cell extracts. Due to single or multiple mismatches in stem regions, the corresponding pre-tRNAs are resistant against the action of human 5′- and 3′-processing enzymes and are thus prevented from being converted to mature tRNAs. Surprisingly, all of them are accurately and efficiently processed to mature-sized tRNA in yeast nuclear extract. This is in agreement with corresponding studies of plant pre-tRNAs which are not processed in wheat germ extract but are rapidly processed in yeast extract. These observations imply that the yeast pre-tRNA 5′-and 3′-maturases do not monitor the three-dimensional structure of their substrates as stringently as mammalian and plant enzymes, possibly because tRNA pseudogenes do not occur in yeast.

PRODUCTION OF OPHIOSTOMA-FREE ADULTS OF IPS SEXDENTATUS BOERN. (COLEOPTERA: SCOLYTIDAE) AND COMPARISON WITH NATURALLY CONTAMINATED ADULTS

AbstractThis study determined the importance of Ophiostomatales fungi in the biology of individual adult Ips sexdentatus Boern. in Scots pine. We investigated factors possibly involved in success of rearing without Ophiostomatales, such as the sterilization technique, the presence of antibiotics, and the absence of yeasts. After sterilization of pupae, 866 adult beetles were reared in the media; the proportion of Ophiostoma-free mature adults was 99.2% and total mortality was about 13%. The most preferred rearing method used sterilized pupae which moulted on moistened filter paper and were transferred individually to separate vials where maturation took place on a sterilized phloem medium.The weight and size of Ophiostoma-free mature adults from semi-artificial media and, after establishment in logs, their fecundity and length of their egg galleries, were compared with those of naturally contaminated mature beetles obtained from logs. With the exception of a higher weight observed for adults matured in semi-artificial media, no essential difference was observed between the two groups. Ophiostomatales do not appear to play an essential role in the maturation and fecundity of I. sexdentatus adults.

Association between gastrointestinal tract carriage of Candida, blood group O, and nonsecretion of blood group antigens in patients with peptic ulcer.

Of 112 patients with peptic ulcer disease examined for oral carriage of Candida, 66 (59%) were carriers. Candida carriage was associated with blood group O (P < 0.05) and, independently, with nonsecretion of blood group antigens (P < 0.01). For each subject, the presence or absence of yeasts was found to be a constant characteristic, and only among patients positive for Candida was blood group O or nonsecretion more frequent than expected in the general population. The quantity of yeasts isolated was significantly greater in patients than in normal subjects (P < 0.002), as was the frequency of carriage in the patient population (59% vs 32%). This increase was not associated with treatment with H2-receptor antagonists. The results of paired oral and gastroduodenal aspirate cultures suggested that identifying Candida in the oral cavity was a good indicator of the presence of yeasts elsewhere in the gastrointestinal tract. Mechanisms whereby overgrowth of Candida in the upper gastrointestinal tract might contribute to the inflammatory background of peptic ulcer disease are discussed.