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D Ramón

Publications and source records attributed to D Ramón.

At least 37 records · Page 2Linked to original sources
PubMed1999

Screening of non-Saccharomyces wine yeasts for the production of beta-D-xylosidase activity.

Fifty-four yeast strains belonging to the genera Candida, Dekkera, Hanseniaspora, Metschnikowia, Pichia, Rhodotorula, Schizosaccharomyces and Zygosaccharomyces, mainly isolated from grapes and wines, were screened for the production of beta-D-xylosidase activity. Beta-D-xylosidase activity was only detected in eight yeast strains belonging to the genera Hanseniaspora (H. osmophila and H. uvarum) and Pichia (P. anomala). Beta-D-xylosidase preparations active against p-nitrophenyl-beta-D-xyloside were characterised with respect to their optimal pH and temperature conditions. H. uvarum 11105 and 11107 and P. anomala 10320 beta-D-xylosidase preparations were active at pH and temperature ranges and at concentrations of glucose and ethanol usually found during winemaking processes.

Ethanol↗
PubMed1999

Genomic stability of Saccharomyces cerevisiae baker's yeasts.

The objective of this study has been to gather data on genomic stability of baker's yeast strains during long-term mitotic growth under restrictive conditions so that comparisons could be made to other studies indicating genomic instability during meiosis. The work describes the analysis of mitotic stability of the nuclear and mitochondrial genomes in the baker's yeast strain V1 during incubation in continuous culture for 190 generations (300 days). The cells were cultured in complete medium containing 2% glucose and 8 to 12% ethanol, as a mutagenic agent specific for mtDNA. The high concentration of ethanol severely limited the growth rate of the cells. DNA samples were monitored for chromosomal pattern, polymorphisms in selected nuclear genes (SUC2, MALIT, ADH1) and mobile genetic elements (Ty1 and Y'), and for RFLPs in mtDNA. The results show that both the nuclear and mitochondrial genomes of grande cells were very stable. However, the frequency of petite mutants in the population varied dramatically during the course of the experiment, reaching as high as 87% petite during the first 27 days of the experiment and declining to 5.8% petite at the end. This decline can be attributed to selection against petite mutants in media containing high concentrations of ethanol. Moreover, when samples and the parental strain were compared at the end of the experiment, no change could be observed in parameters such as their growth rate in different media, capacity to leave doughs, viability in ethanol or frequency of petite mutants. Results therefore indicated that the majority of the cells in the population were very similar to the parental throughout the experiments, with no apparent molecular or phenotypical changes.

Blotting, Southern↗
PubMed1999

Toxicological assessment of recombinant xylanase X(22) in wine.

Toxicological evaluation of xylanase X(22) from Aspergillus nidulans expressed in a wine yeast strain was carried out. The safety of the X(22) intake was assessed by digestibility, bioinformatic, and mouse short-term repeated dosing studies, although X(22) shows resistance to proteolytic degradation in the gastrointestinal system, is a minority protein component (<0.5 10(-)(6) %) of the produced wine, and shows no significant amino acid sequence homology to any known food allergens. The 4-week oral toxicity study was performed in Swiss mice at a dose level of 0.01, 0.1, or 1 mg/kg/day (these dosages correlate to 8, 80, and 800 times, respectively, the enzyme amount contained in 250 mL of wine). Body weight, food and fluid intake, urinalysis, and hematology data were obtained. Postmortem examinations and histopathology by both light and electron microscopy were performed. According to the results of this study, no adverse effects were detected by oral administration of X(22).

Allergens↗
PubMed1999

Carbon catabolite repression of the Aspergillus nidulans xlnA gene.

Expression of the Aspergillus nidulans 22 kDa endoxylanase gene, xlnA, is controlled by at least three mechanisms: specific induction by xylan or xylose; carbon catabolite repression (CCR); and regulation by ambient pH. Deletion analysis of xlnA upstream sequences has identified two positively acting regions: one that mediates specific induction by xylose; and another that mediates the influence of ambient pH and contains two PacC consensus binding sites. The extreme derepressed mutation creAd30 results in considerable, although not total, loss of xlnA glucose repressibility, indicating a major role for CreA in its CCR. Three consensus CreA binding sites are present upstream of the structural gene. Point mutational analysis using reporter constructs has identified a single site, xlnA.C1, that is responsible for direct CreA repression in vivo. Using the creAd30 derepressed mutant background, our results indicate the existence of indirect repression by CreA.

Aspergillus nidulans↗
PubMed1998

Heterologous Expression of a Candida molischiana Anthocyanin-beta-glucosidase in a Wine Yeast Strain.

A recombinant wine yeast strain expressing the Candidamolischiana bgln gene encoding a beta-glucosidase/anthocyanase under the control of the Saccharomyces cerevisiae actin gene promoter has been constructed. The corresponding protein, BGLN, was mainly located on the cell wall. BGLN was purified in a single chromotagraphic step, and different physicochemical and kinetic properties have been determined. BGLN showed maximum activity against the artificial substrate p-nitrophenyl beta-D-glucopyranoside. It also hydrolyzed salicin, p-nitrophenyl beta-D-xyloside, cellobiose, and arbutin to a lesser extent. Fructose and SO(2) did not affect enzyme activity, which was activated by ethanol, while glucose was a strong competitive inhibitor. The purified BGLN showed a novel anthocyanase decolorizing capability on red wines. This anthocyanase activity was readily observed during microvinification experiments. However, the physicochemical characteristics of the wines obtained with the recombinant wine yeast strain were indistinguishable from those obtained with the parental strain.

Journal Article↗
PubMed1998

Molecular cloning and transcriptional regulation of the Aspergillus nidulans xlnD gene encoding a beta-xylosidase.

The xlnD gene encoding the 85-kDa beta-xylosidase was cloned from Aspergillus nidulans. The deduced primary structure of the protein exhibits considerable similarity to the primary structures of the Aspergillus niger and Trichoderma reesei beta-xylosidases and some similarity to the primary structures of the class 3 beta-glucosidases. xlnD is regulated at the transcriptional level; it is induced by xylan and D-xylose and is repressed by D-glucose. Glucose repression is mediated by the product of the creA gene. Although several binding sites for the pH regulatory protein PacC were found in the upstream regulatory region, it was not clear from a Northern analysis whether PacC is involved in transcriptional regulation of xlnD.

Amino Acid Sequence↗
PubMed1998

The role of non-Saccharomyces yeasts in industrial winemaking.

The fermentation of grape juice into wine is a complex microbiological process, in which yeasts play a central role. Traditionally, identification and characterization of yeast species have been based on morphological and physiological characteristics. However, the application of molecular biology techniques represents an alternative to the traditional methods of yeast identification and are becoming an important tool in solving industrial problems. Although Saccharomyces cerevisiae is responsible for the alcoholic fermentation, the presence of non-Saccharomyces species could be important since they produce secondary metabolites, which can contribute to the final taste and flavor of wines.

Industrial Microbiology↗
PubMed1997

Cloning and molecular analysis of the Aspergillus terreus arg1 gene coding for an ornithine carbamoyltransferase.

An Aspergillus terreus gene (arg1) encoding ornithine carbamoyltransferase (OCTase) has been cloned and sequenced. The deduced amino acid sequence contains a signal peptide suggestive of a mitochondrial location for the A. terreus enzyme. Alignment of the A. terreus OCTase sequence with other OCTases revealed the presence of conserved regions. Northern analysis indicates that arg1 expression is regulated at the level of transcription and that transcription of the arg1 gene is not markedly affected by arginine sufficiency. However, histidine starvation effected by 3-amino-1,2,4-triazole increased transcription of the arg1 gene, indicating cross-pathway regulation of OCTase synthesis in A. terreus.

Amino Acids↗
PubMed1997

Trends in wine microbiology.

During the last few years many winemakers have started to use pure Saccharomyces cerevisiae strains, frequently isolated from their own geographical regions, to produce wines of more reproductable quality. This microbiological simplification has opened the way for the genetic modification of wine yeast strains. This review concerns the application of molecular techniques in oenology, not only from the point of view of the construction of recombinant strains but also for the study of the population dynamics of wine fermentations.

Fermentation↗
PubMed1996

Expression in a wine yeast strain of the Aspergillus niger abfB gene.

A recombinant wine yeast strain has been constructed expressing the gene coding for alpha-L-arabinofuranosidase B from Aspergillus niger under the control of the yeast actin gene promoter. The protein is efficiently secreted by the recombinant yeast, allowing its purification and characterisation. The heterologous alpha-L-arabinofuranosidase B shows similar physico-chemical properties to the native enzyme. The wine produced in microvinification experiments using the recombinant yeast presents the same oenological characteristics as obtained with the untransformed strain. The alpha-L-arabinofuranosidase B protein is detected throughout the fermentation.

Aspergillus niger↗
PubMed1996

Identification, isolation and sequence of the Aspergillus nidulans xlnC gene encoding the 34-kDa xylanase.

The xlnC gene encoding the 34-kDa xylanase (X34) of Aspergillus nidulans (An) has been cloned and sequenced, as has its corresponding cDNA. xlnC contains nine introns and shows considerable similarity to the xynA and xylP xylanase-encoding genes of A. kawachii (Ak) and Penicillium chrysogenum (Pc), respectively. Analysis of xylanase production in An multicopy transformants showed elevated levels of X34 and increased total xylanase activity, but no elevated production of other xylanases. Northern analysis demonstrated transcriptional induction by xylan and repression by glucose.

Aspergillus nidulans↗
PubMed1996

Molecular differentiation of Keratinomyces (Trichophyton) species.

The taxonomy of the form-genus Keratinomyces (Trichophyton) within the group of the dermatophytes is based on morphological features which remain insufficient for the distinction of these anamorphic species. The three species included in the genus Keratinomyces, namely K. ajelloi, K. ceretanicus and K. longifusus were examined by means of their mitochondrial-like DNA diversity and compared to few other dermatophytes. The analysis of the mtDNA restriction fragments confirmed that the three species are different and well separate from the other dermatophytes.

Classification↗
PubMed1995

[Applications of molecular biology in the wine industry].

Population dynamics of natural and inoculated industrial wine fermentations have been studied by using a simple molecular biology technique based on mitochondrial DNA restriction analysis profile. The predominance of the inoculated strain in the inoculated fermentations is obvious. A genetic transformation system has been developed for an industrial wine yeast strain named T73. By using this technique, different fungal hydrolases in this industrial strain have been expressed. Problems and benefits of the application of recombinant DNA techniques in wine yeast strains are also discussed here.

Fermentation↗
PubMed1994

Transcriptional regulation of the Trichoderma longibrachiatum egl1 gene.

Transcription of the Trichoderma longibrachiatum egl1 gene is induced in the presence of lactose and beta-methylglucoside and repressed by glucose. A DNA fragment containing 722 bp upstream of the ATG codon has been sequenced. The gene has two major transcription start points (20 and 24 nucleotides upstream from the ATG codon) and several transcription termination points (located in a region around 130 nt downstream of the stop codon). Two 6-mer sequences (5'-CTGGAG-3') separated by 16 bp are present in the egl1 gene promoter. These sequences match the Aspergillus nidulans consensus CreA binding site and might be implicated in carbon catabolite repression of egl1 transcription.

Base Sequence↗