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A E González

Publications and source records attributed to A E González.

16 recordsLinked to original sources
PubMed2005

Short- and long-range topological correlations in two-dimensional aggregation of dense colloidal suspensions.

We have studied the average properties and the topological correlations of computer-simulated two-dimensional (2D) aggregating systems at different initial surface packing fractions. For this purpose, the centers of mass of the growing clusters have been used to build the Voronoi diagram, where each cell represents a single cluster. The number of sides (n) and the area (A) of the cells are related to the size of the clusters and the number of nearest neighbors, respectively. We have focused our paper in the study of the topological quantities derived from number of sides, n , and we leave for a future work the study of the dependence of these magnitudes on the area of the cells, A . In this work, we go beyond the adjacent cluster correlations and explore the organization of the whole system of clusters by dividing the space in concentric layers around each cluster: the shell structure. This method allows us to analyze the time behavior of the long-range intercluster correlations induced by the aggregation process. We observed that kinetic and topological properties are intimately connected. Particularly, we found a continuous ordering of the shell structure from the earlier stages of the aggregation process, where clusters positions approach a hexagonal distribution in the plane. For long aggregation times, when the dynamic scaling regime is achieved, the short- and long-range topological properties reached a final stationary state. This ordering is stronger for high particle densities. Comparison between simulation and theoretical data points out the fact that 2D colloidal aggregation in the absence of interactions (diffusion-limited cluster aggregation regimen) is only able to produce short-range cluster-cluster correlations. Moreover, we showed that the correlation between adjacent clusters verifies the Aboav-Weaire law, while all the topological properties for nonadjacent clusters are mainly determined by only two parameters: the second central moment of number-of-sides distribution mu(2) = sumP (n) (n-6)(2) and the screening factor a (defined through the Aboav-Weaire equation). We also found that the values of mu(2) and a calculated for two-dimensional aggregating system are related through a single universal common form a proportional to mu2(-0.89), which is independent of the particle concentration.

Journal Article↗
PubMed2004

Tannic acid interferes with the commonly used laccase-detection assay based on ABTS as the substrate.

Laccase enzymatic activity in biological samples is usually detected spectrophotometrically through its capacity to oxidize several specific aromatic compounds. One of the most commonly used substrates is the compound 2-2'-azinobis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), which becomes green-blue coloured when it is oxidized by laccase. In this work we study the interference of tannic acid with the spectrophotometric assay to detect laccase by using ABTS as the substrate. Our data show that under the normal reaction conditions of this assay, but in the absence of any catalyst, tannic acid is able to carry out the chemical reduction of the oxidized specie of ABTS, thus decreasing the overall detectable laccase-activity values observed when this enzyme is present in the reaction mixture. Therefore, our results represent an important warning concerning a commonly used method for measuring, detecting or screening laccases in biological samples that may content tannic acid or structural-related molecules.

Benzothiazoles↗
PubMed2004

Ecological study of the fungal populations of the acidic Tinto River in southwestern Spain.

The characterization of the microbial ecology of the Tinto River, an extreme habitat with an extremely low pH and a high concentration of heavy metals, revealed an unexpected level of microbial richness. A variety of microbial eukaryotes was isolated, among them several fungal strains that were identified and their physiological characteristics studied. Ninety strains of yeast were isolated from the Tinto River. Fifty-two percent of them were capable of growth in vitro using medium amended with river water. They belong to 6 genera of basidiomycetes (Rhodotorula, Cryptococcus, Tremella, Holtermannia, Leucosporidium, and Mrakia) and 2 of ascomycetes (Candida and Williopsis). In addition, 349 strains of hyphomycetes belonging to 17 genera (most of them ascomycetes) were isolated and studied. Forty-four percent of the isolated filamentous fungi (154 strains) were capable of growing in vitro using medium amended with Tinto River water. Of this percentage, 19% (29 strains) belonged to the genus Penicillium (16 species) and 66% (102 strains) were included in the genera Scytalidium, Bahusakala, Phoma, and Heteroconium or showed dark sterile mycelia, which probably are of dematiaceous hyphomycetes. In addition, we characterized strains of the ascomycete genera Lecythophora and Acremonium and of the zygomycete genus Mortierella, all of them capable of growing in medium amended with river water. Statistical correlation of biological and physicochemical variables suggested a positive relationship between the dematiaceous hyphomycetes and the most extreme physicochemical conditions found in the Tinto River. Principal components analysis confirmed this relationship and also showed that the Acremonium and Lecythophora groups had environmental preferences similar to those of dematiaceous fungi. The spatial positions of the sampling sites were grouped in 2 main clusters: (i) sampling sites in the mine zone in which most of the dematiaceous, Acremonium, and Lecythophora strains were isolated and (ii) sites that were not in the mine zone and sampling station 5 from which were isolated mainly strains of fungi that were not capable of growing in the medium amended with river water and species of the Penicillium genus.

Culture Media↗
PubMed2004

Colloidal aggregation with sedimentation: concentration effects.

The results of computer models for colloidal aggregation, that consider both Brownian motion and gravitational drift experienced by the colloidal particles and clusters, are extended to include concentrations spanning three orders of magnitude. In previous publications and for a high colloidal concentration, it was obtained that the aggregation crosses over from diffusion-limited colloidal aggregation (DLCA) to another regime with a higher cluster fractal dimension and a speeding up followed by a slowing down of the aggregation rate. In the present work we show, as the concentration is decreased, that we can still cross over to a similar regime during the course of the aggregation, as long as the height of the sample is increased accordingly. Among the differences between the mentioned new regimes for a high and a low colloidal concentration, the cluster fractal dimension is higher for the high concentration case and lowers its value as the concentration is decreased, presumably reaching for low enough concentrations a fixed value above the DLCA value. It is also obtained the fractal dimension of the sediments, arising from the settling clusters that reach the bottom and continue a 2D-like diffusive motion and aggregation, on the floor of the container. For these clusters we now see two and sometimes three regimes, depending on concentration and sedimentation strength, with their corresponding fractal dimensions. The first two coming from the crossover already mentioned, that took place in the bulk of the sample before the cluster deposition, while the third arises from the two-dimensional aggregation on the floor of the container. For these bottom clusters we also obtain their dynamical behavior and aggregation rate.

Algorithms↗
PubMed2001

Colloidal aggregation with sedimentation: computer simulations.

A computer model for colloidal aggregation is presented that considers both the Brownian motion and the gravitational drift experienced by the colloidal particles and clusters. It is shown that the aggregation crosses over from diffusion-limited aggregation to another type with a higher cluster fractal dimension, a speeding up followed by a slowing down of the aggregation rate, an algebraically decaying cluster size distribution, and a higher concentration required for gelation. Although these findings are in accordance with the experimental results, some interpretations are different.

Journal Article↗
PubMed2000

Biotreatment of tannin-rich beer-factory wastewater with white-rot basidiomycete Coriolopsis gallica monitored by pyrolysis/gas chromatography/mass spectrometry.

Some fractions of beer-factory wastewaters represent an important environmental concern owing to their high content of polyphenols and dark-brown color. The capacity of Coriolopsis gallica to preferentially degrade lignin has been successfully applied in our laboratory to the biotreatment and decolorization of paper-industry effluents. In this work, the ability of this white-rot fungus to degrade high-tannin-containing wastewaters is evaluated. Under all the conditions studied, effluent decolorization and chemical oxygen demand reduction achieved by C. gallica at day 12 of incubation were close to 50 and 65%, respectively. No adhesion of dark color to the fungal mycelium was observed suggesting that decolorization could be ascribed to C. gallica degradation systems. Mycelium dry-weight values showed that C. gallica is tolerant to relatively high tannin content present in the effluent samples. In the sample containing the highest effluent concentration (60% v/v), dry-weight values suggested an inhibition of fungal growth at day 6 of incubation and a further adaptation of the fungus to the stressing tannin effect at day 12 of fungal treatment. Pyrolysis/gas chromatography/mass spectrometry results showed a decrease of polyphenols pyrolysis products, mainly phenol and guaiacol, with the incubation time. All these results indicate the potential use of C. gallica in bioremediation of tannin-containing industrial wastewaters and in other applications where a reduction in polyphenols content is required.

Beer↗
PubMed2000

Pyrolysis/gas chromatography/mass spectrometry monitoring of fungal-biotreated distillery wastewater using Trametes sp. I-62 (CECT 20197).

Distillery wastewaters generated by ethanol production from fermentation of sugar-cane molasses, named vinasses, lead to important ecological impact due to their high content of soluble organic matter and their intense dark-brown color. Taking advantage of the well-known ability of white-rot fungi to degrade an extensive variety of organic pollutants, the capacity of Trametes sp. I-62 (CECT 20197) to detoxify this type of effluents was evaluated. In this work, pyrolysis/gas chromatography/mass spectrometry was applied to the chemical characterization of several fractions of Cuban distillery wastewater as well as to monitoring the changes which occurred after fungal treatment with this white-rot basidiomycete. Maximum effluent decolorization values and chemical oxygen demand reduction attained after seven days of fungal treatment were 73.3 and 61.7%, respectively, when 20% (v/v) of distillery vinasses was added to the culture medium. Under these conditions a 35-fold increase in laccase production by Trametes sp. I-62 was measured, but no manganese peroxidase activity could be detected. The pyrolysis/gas chromatography/mass spectrometry results showed a decrease in a number of pyrolysis products after seven days of fungal treatment, mainly furan derivatives. The decrease in the relative areas of these compounds could be related to the vinasse color-removal associated with melanoidin degradation. All these results indicated the potential use ofTrametes sp. I-62 in the detoxification of recalcitrant distillery vinasses.

Fermentation↗
PubMed2000

[Congenital dysplasia of tricuspid valve (Ebstein like) in a 73-year-old male with severe tricuspid insufficiency].

Multiple congenital abnormalities in the structure of the tricuspid valve have been described and, the majority of cases could be considered as variations of Ebstein's anomaly. The onset of the symptoms and the diagnosis depend on the severity of the valve dysfunction and the right ventricular function and size. The age at diagnosis ranges from birth to adulthood, but a delayed diagnosis is rare when tricuspid regurgitation is severe. We cite as an example the case of a 73 year-old male classified as class I of the NYHA up to 5 months before, since then he developed progressive ascitis and edema on his legs. The physical examination suggested severe tricuspid regurgitation. We performed a transtoracic and transesophageal ecocardiogram that showed severe dysplasia in the tricuspid leaflets, severe regurgitation because of lack of adequate joining, dilatation of right chambers and right ventricular systolic dysfunction.

Aged↗
PubMed2000

Colloidal aggregation with mobile impurities.

The structure and aggregation kinetics of diffusion-limited cluster-cluster three-dimensional monomeric aggregates and gels is investigated as a function of the molar fraction of two types of impurities. In one case the impurities are allowed to aggregate among themselves whereas in the other the impurities are mobile monomers that remain as such during the whole aggregation process. Computer simulations are performed on a simple cubic lattice for which the functionality of the aggregating particles is effectively 6. The first type of impurity shows a decrease in the fractal dimension when compared to that of a one component system at the same concentration. As a consequence of this decrease, the gelation concentration is lowered. At higher concentrations a gelling to nongelling transition was observed. In the nongelling regime the colloidal aggregates are kept apart by the impurity clusters, developing a local ordering. For the monomeric type of impurity, at large impurity molar fractions, a nonstructured nongelling phase appears at high enough concentration, in which the colloidal aggregates are kept apart by the sea of mobile impurities that inhibits the formation of a gel. Smaller molar fractions of mobile monomeric impurities strongly affect both the fractal dimension and the kinetics of the aggregating colloid.

Algorithms↗
PubMed1998

Differential Gene Expression in the Laccase Gene Family from Basidiomycete I-62 (CECT 20197).

A family of genes encoding laccases has recently been described for the basidiomycete I-62 (CECT 20197). Transcript levels of genes lcc1, lcc2, and lcc3 were analyzed under four different culture conditions to study their expression patterns. Two of the laccase genes were clearly inducible by veratryl alcohol: the lcc1 gene is inducible in early stages of growth, and the lcc2 gene is also inducible but only when the organism reaches the stationary phase. Transcript levels for the third gene, lcc3, were uninduced by veratryl alcohol and repressed by glucose.

Journal Article↗
PubMed1997

Identification of a laccase gene family in the new lignin-degrading basidiomycete CECT 20197.

A new lignin-degrading basidiomycete, strain I-62 (CECT 20197), isolated from decayed wood exhibited both a high dephenolization activity and decolorization capacity when tested on effluents from the sugar cane by-product fermentation industry. It has been classified as a member of the Polyporaceae family. The major ligninolytic activity detected in culture supernatants of basidiomycete I-62 was a phenoloxidase (laccase), in conjunction with small amounts of manganese peroxidase. No lignin peroxidase was detected. Laccase activity was produced in either defined or complete media. Addition of veratryl alcohol as the inducer, in defined medium, enhanced laccase production 10-fold. The use of fructose instead of glucose as a carbon source resulted in a 100-fold increase in laccase specific activity. Native isoelectrofocusing gels stained with guaiacol revealed the presence of at least seven laccase isozymes, with the most intense band being detected at pI 3. Southern hybridization analysis indicated the presence of a laccase gene family in strain I-62. Three different genes coding for phenoloxidases, lcc1, lcc2, and lcc3, were cloned and characterized. The high degree of homology between laccases from strain I-62 and laccases from Trametes species suggests a phylogenetic proximity between this new isolated fungus and the genus Trametes.

Amino Acid Sequence↗
PubMed1989

A study of yeasts during the delignification and fungal transformation of wood into cattle feed in Chilean rain forest.

In Chilean rain forest the presence and distribution of yeasts were studied during the fungal transformation of wood, producing a partially delignified material used as cattle feed ("huempe"). A total of 68 yeast species was reported, including a noticeable proportions of basidiomycetous and xylose-assimilating strains, the latter related to the increased availability of this sugar in the decayed wood. The results of the mathematic comparison of taxonomic data of 327 strains showed a delimitation of sharp clusters corresponding to different species, including several new species described from this substrate, and genera, as Rhodotorula and Cryptococcus. At the initial stages of wood decay, characterized by the presence of Candida species, yeast diversity was low. The highest values were found in the medium stage of decay, used as feed, with an important presence of the genera Apiotrichum, Rhodotorula, Cryptococcus and Schizoblastosporion. After establishing a non-linear ordination from Euclidean distances between samples, based on yeast abundances, a relationship was observed between the populations developing at the different stages of wood decay by Ganoderma applanatum. A succession of yeast species was demonstrated during wood degradation by this white-rot fungus.

Animal Feed↗