Consulta: subjectFacets:"Exopolysaccharides"
Registros recuperados: 20
Data/hora: 09/06/2024 05:42:59

Optimization of culture conditions for exopolysaccharides production in Rhizobium sp. using the response surface method
Provedor de dados: 69
Autores: Pereira Duta,Flávia; Pessôa de França,Francisca; de Almeida Lopes,Léa Maria.
The combined effects of the processing parameters for exopolysaccharides production by Rhizobium sp. was studied using the experimental design and response surface methodology. The experiments were carried out using a fermenter with 20 L capacity, as the reactor. All processing parameters were online monitored. The temperature [(30 &amp;plusmn; 1)&amp;ordm;C] and pH value (7.0 &amp;plusmn; 0.1) were kept constant throughout the experimental time. As statistical tools, a complete 2³ factorial planning with central point and response surface were used to study the interactions among three relevant variables of the fermentation process: calcium carbonate concentration, aeration and agitation. The processing parameters setup for reaching a maximum response for...
Tipo: Journal article
Palavras-chave: Exopolysaccharides; Experimental design; Response surface method; Rhizobium sp.
Ano: 2006
URL: http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-34582006000400007

Concentration and purification of Porphyridium cruentum exopolysaccharides by membrane filtration at various cross-flow velocities
Provedor de dados: 5
Autores: Balti, Rafik; Le Balc'H, Romain; Brodu, Nicolas; Gilbert, Marthe; Le Gouic, Benjamin; Le Gall, Sophie; Sinquin, Corinne; Masse, Anthony.
Exopolysaccharides (EPS) from cell-free Porphyridium cruentum media were concentrated then purified (diafiltration) on a 0.14 µm ceramic membrane. The influence of cross-flow velocities on filtration performances was investigated. Mean permeate fluxes equal to 49.8, 68.9 and 81.9 L.h-1. m-2 were obtained during the concentration at 4 bar for respectively cross-flow velocities inside the membrane lumen equal to 2.5, 3.3 and 4.2 m.s-1; 49.7 L.h-1. m-2 for the diafiltration at 3.3 m.s-1. Permeate fluxes were correctly predicted from polysaccharide concentrations (10 % deviation). Volume reduction factors higher than 7.8 were reached. Rejection rates of polysaccharides and proteins varied according to the cross-flow velocities. Thus, the EPS recovery rate or...
Tipo: Text
Palavras-chave: Membrane filtration; Exopolysaccharides; Microalga; Concentration; Diafiltration.
Ano: 2018
URL: https://archimer.ifremer.fr/doc/00445/55694/57360.pdf

Effects of incubation temperature on growth and production of exopolysaccharides by an Antarctic sea ice bacterium grown in batch culture
Provedor de dados: 5
Autores: Nichols, Carol; Bowman, John; Guezennec, Jean.
The sea ice microbial community plays a key role in the productivity of the Southern Ocean. Exopolysaccharide (EPS) is a major component of the exopolymer secreted by many marine bacteria to enhance survival and is abundant in sea ice brine channels, but little is known about its function there. This study investigated the effects of temperature on EPS production in batch culture by CAM025, a marine bacterium isolated from sea ice sampled from the Southern Ocean. Previous studies have shown that CAM025 is a member of the genus Pseudoalteromonas and therefore belongs to a group found to be abundant in sea ice by culture-dependent and -independent techniques. Batch cultures were grown at -2 degrees C, 10 degrees C, and 20 degrees C, and cell number, optical...
Tipo: Text
Palavras-chave: EPS yield; Psychrotolerant; Sea ice; Marine bacteria; Antarctica; Exopolymer; Exopolysaccharides.
Ano: 2005
URL: http://archimer.ifremer.fr/doc/2005/publication-625.pdf

Production of exopolysaccharides by Antarctic marine bacterial isolates
Provedor de dados: 5
Autores: Nichols, C; Garon, Sandrine; Bowman, J; Raguenes, Gerard; Guezennec, Jean.
Aims: This study was undertaken to examine and characterize Antarctic marine bacterial isolates and the exopolysaccharides (EPS) they produce in laboratory culture.   Methods and Results: Two EPS-producing bacterial strains CAM025 and CAM036 were isolated from particulate material sampled from seawater and sea ice in the southern ocean. Analyses of 16S rDNA sequences placed these isolates in the genus Pseudoalteromonas. In batch culture, both strains produced EPS. The yield of EPS produced by CAM025 was 30-fold higher at -2 and 10degreesC than at 20degreesC. Crude chemical analyses showed that these EPS were composed primarily of neutral sugars and uronic acids with sulphates. Gas chromatographic analysis of monosaccharides confirmed these gross...
Tipo: Text
Palavras-chave: Sea ice; Pseudoalteromonas spp.; Particulate organic material; Exopolysaccharides; Antarctic marine bacteria.
Ano: 2004
URL: https://archimer.ifremer.fr/doc/2004/publication-629.pdf

Bioprospecting for Exopolysaccharides from Deep-Sea Hydrothermal Vent Bacteria: Relationship between Bacterial Diversity and Chemical Diversity
Provedor de dados: 5
Autores: Delbarre-ladrat, Christine; Salas, Marcia Leyva; Sinquin, Corinne; Zykwinska, Agata; Colliec-jouault, Sylvia.
Many bacteria biosynthesize structurally diverse exopolysaccharides (EPS) and excrete them into their surrounding environment. The EPS functional features have found many applications in industries such as cosmetics and pharmaceutics. In particular, some EPS produced by marine bacteria are composed of uronic acids, neutral sugars, and N-acetylhexosamines, and may also bear some functional sulfate groups. This suggests that they can share common structural features with glycosaminoglycans (GAG) like the two EPS (HE800 and GY785) originating from the deep sea. In an attempt to discover new EPS that may be promising candidates as GAG-mimetics, fifty-one marine bacterial strains originating from deep-sea hydrothermal vents were screened. The analysis of the...
Tipo: Text
Palavras-chave: Exopolysaccharides; GAG; Marine bacteria; Glycopolymers; Sulfate; Production.
Ano: 2017
URL: https://archimer.ifremer.fr/doc/00399/51090/51873.pdf

Antiproliferative Properties of Scandium Exopolysaccharide Complexes on Several Cancer Cell Lines
Provedor de dados: 5
Autores: Muñoz-garcia, Javier; Mazza, Mattia; Alliot, Cyrille; Sinquin, Corinne; Colliec-jouault, Sylvia; Heymann, Dominique; Huclier-markai, Sandrine.
Antimetastatic properties on both murine and human osteosarcoma cell lines (POS-1 and KHOS) have been evidenced using exopolysaccharide (EPS) derivatives, produced by Alteromonas infernus bacterium. These derivatives had no significant effect on the cell cycle neither a pro-apoptotic effect on osteosarcoma cells. Based on this observation, these EPSs could be employed as new drug delivery systems for therapeutic uses. A theranostic approach, i.e., combination of a predictive biomarker with a therapeutic agent, has been developed notably by combining with true pair of theranostic radionuclides, such as scandium 47Sc/44Sc. However, it is crucial to ensure that, once complexation is done, the biological properties of the vector remain intact, allowing the...
Tipo: Text
Palavras-chave: Exopolysaccharides; Scandium; Theranostic; Cancer cell lines; Proliferation.
Ano: 2021
URL: https://archimer.ifremer.fr/doc/00686/79826/82630.pdf

Characterization of New Oligosaccharides Obtained by An Enzymatic Cleavage of the Exopolysaccharide Produced by the Deep-Sea Bacterium Alteromonas infernus Using its Cell Extract
Provedor de dados: 5
Autores: Akoumany, Katy; Zykwinska, Agata; Sinquin, Corinne; Marchand, Laetitia; Fanuel, Mathieu; Ropartz, David; Rogniaux, Hélène; Pipelier, Muriel; Delbarre Ladrat, Christine; Colliec Jouault, Sylvia.
Bacteria from deep-sea hydrothermal vents constitute an attractive source of bioactive molecules. In particular, exopolysaccharides (EPS) produced by these bacteria become a renewable source of both biocompatible and biodegradable molecules. The low molecular weight (LMW) derivatives of the GY785 EPS produced by the deep-sea hydrothermal vent strain Alteromonas infernus have previously displayed some biological properties, similar to those of glycosaminoglycans (GAG), explored in cancer and tissue engineering. These GAG-mimetic derivatives are obtained through a free radical depolymerization process, which could, however, affect their structural integrity. In a previous study, we have shown that A. infernus produces depolymerizing enzymes active on its own...
Tipo: Text
Palavras-chave: Deep-sea bacterium; Alteromonas infernus; Wild-type strain; Exopolysaccharides; Glycosaminoglycan-mimetic; Enzymatic depolymerization; Structural analysis; Mass spectrometry.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00515/62644/67021.pdf

Marine Polysaccharides: A Source of Bioactive Molecules for Cell Therapy and Tissue Engineering
Provedor de dados: 5
Autores: Senni, Karim; Pereira, Jessica; Gueniche, Farida; Delbarre-ladrat, Christine; Sinquin, Corinne; Ratiskol, Jacqueline; Godeau, Gaston; Fischer, Anne-marie; Helley, Dominique; Colliec-jouault, Sylvia.
The therapeutic potential of natural bioactive compounds such as polysaccharides, especially glycosaminoglycans, is now well documented, and this activity combined with natural biodiversity will allow the development of a new generation of therapeutics. Advances in our understanding of the biosynthesis, structure and function of complex glycans from mammalian origin have shown the crucial role of this class of molecules to modulate disease processes and the importance of a deeper knowledge of structure-activity relationships. Marine environment offers a tremendous biodiversity and original polysaccharides have been discovered presenting a great chemical diversity that is largely species specific. The study of the biological properties of the...
Tipo: Text
Palavras-chave: Marine bacteria; Marine algae; Exopolysaccharides; Sulfated polysaccharides; Structure; Chemical modification; Biological activity; Blue biotechnology; Cell therapy; Tissue engineering.
Ano: 2011
URL: http://archimer.ifremer.fr/doc/00048/15894/13316.pdf

Marine Exopolysaccharide Complexed with Scandium Aimed as Theranostic Agents
Provedor de dados: 5
Autores: Mazza, Mattia; Alliot, Cyrille; Sinquin, Corinne; Colliec-jouault, Sylvia; Reiller, Pascal E.; Huclier-markai, Sandrine.
Background: Exopolysaccharide (EPS) derivatives, produced by Alteromonas infernus bacterium, showed anti-metastatic properties. They may represent a new class of ligands to be combined with theranostic radionuclides, such as 47Sc/44Sc. The goal of this work was to investigate the feasibility of such coupling. (2) Methods: EPSs, as well as heparin used as a drug reference, were characterized in terms of molar mass and dispersity using Asymmetrical Flow Field-Flow Fractionation coupled to Multi-Angle Light Scattering (AF4-MALS). The intrinsic viscosity of EPSs at different ionic strengths were measured in order to establish the conformation. To determine the stability constants of Sc with EPS and heparin, a Free-ion selective radiotracer extraction (FISRE)...
Tipo: Text
Palavras-chave: Exopolysaccharides; Scandium; Theranostic; Characterization; Complexation.
Ano: 2021
URL: https://archimer.ifremer.fr/doc/00681/79332/81844.pdf

Chemical characterization of exopolysaccharides from Antarctic marine bacteria
Provedor de dados: 5
Autores: Nichols, Carol; Lardiere, Sandrine; Bowman, John; Nichols, Peter; Gibson, John; Guezennec, Jean.
Exopolysaccharides (EPS) may have an important role in the Antarctic marine environment, possibly acting as ligands for trace metal nutrients such as iron or providing cryoprotection for growth at low temperature and high salinity. Ten bacterial strains, isolated from Southern Ocean particulate material or from sea ice, were characterized. Whole cell fatty acid profiles and 16S rRNA gene sequences showed that the isolates included representatives of the genera Pseudoalteromonas, Shewanella, Polaribacter, and Flavobacterium as well as one strain, which constituted a new bacterial genus in the family Flavobacteriaceae. The isolates are, therefore, members of the "Gammaproteobacteria" and Cytophaga-Flexibacter-Bacteroides, the taxonomic groups that have been...
Tipo: Text
Palavras-chave: Marine particulates; Sea ice; Marine bacteria; Antarctica; Exopolysaccharides.
Ano: 2005
URL: http://archimer.ifremer.fr/doc/2005/publication-623.pdf

Exopolysaccharides produced by bacteria isolated from deep-sea hydrothermal vents: new agents with therapeutic potential
Provedor de dados: 5
Autores: Colliec-jouault, Sylvia; Zanchetta, P; Helley, D; Ratiskol, Jacqueline; Sinquin, Corinne; Fischer, A. M.; Guezennec, Jean.
Bacterial polysaccharides offer fascinating potential applications for the pharmaceutical industry. Although many known marine bacteria produce exopolysaccharides (EPS), continuation in looking for new polysaccharide-producing micro-organisms is promising. Marine bacteria, isolated from deep-sea hydrothermal vents, have demonstrated their ability to produce in aerobic conditions, unusual EPS. With the aim of discovering biological activities, EPS presenting different structural features were studied. An EPS secreted by Vibrio, diabolicus was evaluated on the restoration of bone integrity in experimental model and was demonstrated to be a strong bone-healing material. Another EPS produced by Alteromonas infernus was modified in order to obtain new...
Tipo: Text
Palavras-chave: Hydrothermal vents; Exopolysaccharides; Bone healing; Biomimetic; Anticoagulant activity; Sources hydrothermales; Exopolysaccharide; Cicatrisation osseuse; Biomimétique; Activité anticoagulante.
Ano: 2004
URL: http://archimer.ifremer.fr/doc/2004/publication-2117.pdf

Dérivés de l'exopolysaccharide d’Alteromonas infernus, mimétiques de glycosaminoglycanes, et développement d'une stratégie pour leur analyse structurale
Provedor de dados: 5
Autores: Akoumany, Katy.
In search of new bioactive compounds, marine bacteria constitute a considerable source of innovative molecules. The bacterial exopolysaccharide (EPS), produced by the deep-sea hydrothermal vent strain Alteromonas infernus, is a high-molecular-weight, highly branched and anionic heteropolysaccharide with a nonasaccharide repeating unit. This macromolecule and its low-molecular-weight derivatives obtained through a chemical process have previously displayed interesting GAG-like properties such as anti-metastatic and anti-coagulant (heparin-like) ones; they can also improve stem cell differentiation. To investigate the molecular bases of the biological activity and to facilitate the structural analysis of the bioactive derivatives (~20 000 g/mol), fragments...
Tipo: Text
Palavras-chave: Bactérie marine; Exopolysaccharides; Dépolymérisation enzymatique; Synthèse organique; Marine bacteria; Exopolysaccharides; Enzymatic depolymerisation; Organic synthesis.
Ano: 2019
URL: https://archimer.ifremer.fr/doc/00605/71733/70206.pdf

Anti-Metastatic Properties of a Marine Bacterial Exopolysaccharide-Based Derivative Designed to Mimic Glycosaminoglycans
Provedor de dados: 5
Autores: Heymann, Dominique; Ruiz-velasco, Carmen; Chesneau, Julie; Ratiskol, Jacqueline; Sinquin, Corinne; Colliec-jouault, Sylvia.
Osteosarcoma is the most frequent malignant primary bone tumor characterized by a high potency to form lung metastases. In this study, the effect of three oversulfated low molecular weight marine bacterial exopolysaccharides (OS-EPS) with different molecular weights (4, 8 and 15 kDa) were first evaluated in vitro on human and murine osteosarcoma cell lines. Different biological activities were studied: cell proliferation, cell adhesion and migration, matrix metalloproteinase expression. This in vitro study showed that only the OS-EPS 15 kDa derivative could inhibit the invasiveness of osteosarcoma cells with an inhibition rate close to 90%. Moreover, this derivative was potent to inhibit both migration and invasiveness of osteosarcoma cell lines; had no...
Tipo: Text
Palavras-chave: Exopolysaccharides; Glycosaminoglycan; Heparin-like; Derivatives; Sulfation; Bone metabolism; Bone remodeling; Lung mestatases; Osteosarcoma.
Ano: 2016
URL: https://archimer.ifremer.fr/doc/00333/44442/44112.pdf

Microbial mats in French Polynesia and their biotechnological applications
Provedor de dados: 5
Autores: Guezennec, Jean; Moppert, Xavier; Raguenes, Gerard; Richert, Laurent; Costa, Bernard; Simon-colin, Christelle.
It is well known that microorganisms well-adapted to survival in extreme ecosystems could be considered as new sources of biomolecules that have biotechnological importance. On French Polynesian atolls, microbial mats are developing in water ponds exposed to fluctuations in physical and chemical parameters. In these microbial mats, which are called "kopara" by the inhabitants, bacteria coexist with cyanobacteria, and a synergistic relationship may exist between these two types of living microorganisms. A large number of cyanobacteria and bacteria have been isolated from different mats. Under laboratory conditions, these microorganisms were shown to produce various exopolymers, including exopolysaccharides and poly-beta-hydroxyalkanoates, along with...
Tipo: Text
Palavras-chave: Microbial mats; Kopara; Biopolymers; Exopolysaccharides; Poly-beta-hydroxyalkanoates.
Ano: 2011
URL: http://archimer.ifremer.fr/doc/00029/14058/11423.pdf

Etude d'oligosaccharides bioactifs issus d'exopolysaccharides bactériens : obtention, caractérisation et relation structure/fonction
Provedor de dados: 5
Autores: Roger, Olivier.
Unusual exopolysaccharides (EPS) produced by heterotrophic aerobic and mesophilic bacteria originating from hydrothermal vent, were reviewed as a new source of polysaccharidic structures endowed with innovative biological properties. The first step of this study was the structure determination of the EPS GY785, synthesized by Alteromonas infernus. A highly branched nonasaccharidic repetitive unit was identified using chemical modifications and nuclear magnetic resonance spectroscopy. This 106 g/mol polysaccharide is composed of glucose, galactose, glucuronic acid, galacturonic acid, and contains a single branched ramification and one sulphate group.  The second step was the preparation of low molecular weight bioactive polysaccharides presenting interest...
Tipo: Text
Palavras-chave: Phosphorylation; Sulphation; Depolymerization; NMR spectroscopy; Structure; Deep sea hydrothermal vent; Bacteria; Exopolysaccharides; Activité anticoagulante; Phosphatation; Sulfatation; Dépolymérisation; Spectroscopie de RMN; Structure; Sources hydrothermales; Bactéries; Exopolysaccharides.
Ano: 2002
URL: http://archimer.ifremer.fr/doc/2002/these-622.pdf

Exopolysaccharides produced by the symbiotic nitrogen-fixing bacteria of leguminosae
Provedor de dados: 90
Autores: Bomfeti,Cleide Aparecida; Florentino,Ligiane Aparecida; Guimarães,Ana Paula; Cardoso,Patrícia Gomes; Guerreiro,Mário César; Moreira,Fatima Maria de Souza.
The process of biological nitrogen fixation (BNF), performed by symbiotic nitrogen fixing bacteria with legume species, commonly known as α and β rhizobia, provides high sustainability for the ecosystems. Its management as a biotechnology is well succeeded for improving crop yields. A remarkable example of this success is the inoculation of Brazilian soybeans with Bradyrhizobium strains. Rhizobia produce a wide diversity of chemical structures of exopolysaccharides (EPS). Although the role of EPS is relatively well studied in the process of BNF, their economic and environmental potential is not yet explored. These EPS are mostly species-specific heteropolysaccharides, which can vary according to the composition of sugars, their linkages in a single...
Tipo: Info:eu-repo/semantics/article
Palavras-chave: Exopolysaccharides; Nodules; Environmental stress; Soil aggregation; Rhizobia.
Ano: 2011
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0100-06832011000300001

Fermentation characteristics in stirred-tank reactor of exopolysaccharides with hypolipidemic activity produced by Pleurotus geesteranus5#
Provedor de dados: 42
Autores: DUOBIN,MAO; YUPING,MA; LUJING,GENG; AIJING,ZHAO; JIANQIANG,ZHENG; CHUNPING,XU.
In this study, the hypolipidemic effect of exopolysaccharides (EPS) fromPleurotus geesteranus 5# fermenting liquor by the optimal culture conditions in a 5-L stirred-tank reactor was investigated. The hypolipidemic effect of the polysaccharide, investigated in streptozotocin induced diabetic mice, decreased plasma glucose, total cholesterol and triacylglycerol concentrations by 17.1 %, 18.8 % and 12.0 %, respectively. The results of the present investigation strongly demonstrate the potential of this polysaccharide to prevent hyperglycemia in the experimental animals. Under optimal culture conditions, the maximum concentrations of mycelial and EPS were 22.63 g/L after 7 d cultivation and 11.09 g/L after 10 d, respectively. Furthermore, the morphological...
Tipo: Info:eu-repo/semantics/article
Palavras-chave: Exopolysaccharides; Pleurotus geesteranus; Fermentation; Hypolipidemic effect; Morphology.
Ano: 2013
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652013000401473

Effects of cigarette smoke condensate on the production and characterization of exopolysaccharides by Bifidobacterium
Provedor de dados: 42
Autores: Hu,Jinqiang; Wei,Tao; Sun,Siwen; Zhao,Aijing; Xu,Chunping.
The aim of the study was to investigate the effect of cigarette smoke on the production and characterization of exopolysaccharides (EPSs) produced by Bifidobacterium. Cigarettes of Shanhua brand (nicotine: 1.1 mg, tar: 11 mg) were utilized to prepare a cigarette smoke condensate (CSC). The standard strain of Bifidobacterium animalis was cultured in MRS media under anaerobic addition of CSC. The results showed that CSC significantly decreased the growth of B. animalis as well as EPSs and acetic acid production. Furthermore, two EPSs fractions (Fr-I and Fr-II) were isolated and purified for chemical and molecular determination. By comparison with control, CSC was found to be of great impact on EPSs carbohydrate composition. The molecular weight mass of Fr-I...
Tipo: Info:eu-repo/semantics/article
Palavras-chave: Exopolysaccharides; Cigarette smoke condensate; Bifidobacterium; Acetic acid.
Ano: 2015
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0001-37652015000200997

Production of biopolymers by Pseudomonas aeruginosa isolated from marine source
Provedor de dados: 52
Autores: Jamil,Nazia; Ahmed,Nuzhat.
Two bacterial strains, Pseudomonas aeruginosa CMG607w and CMG1421 produce commercially important biopolymers. CMG607w isolated from the sediments of Lyari outfall to Arabian Sea synthesize the mcl-polyhydroxyalkanoates from various carbon sources. The production of PHAs was directly proportional to the incubation periods. Other strain CMG1421, a dry soil isolate, produced high viscous water absorbing extracellular acidic polysaccharide when it was grown aerobically in the minimal medium containing glucose or fructose or sucrose as sole source of carbon. The biopolymer had the ability to absorb water 400 times more than its dry weight. This property was superior to that of currently used non-degradable synthetic water absorbents. It acted as salt filter and...
Tipo: Info:eu-repo/semantics/article
Palavras-chave: Biopolymers; Exopolysaccharides; Hydroabsorbent; Mcl-polyhydroxyalkanoates; Pseudomonas aeruginosa; Sodium gluconate.
Ano: 2008
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1516-89132008000300004

Optimization of exopolysaccharides production from a novel strain of Ganoderma lucidum CAU5501 in submerged culture
Provedor de dados: 58
Autores: Yuan,Baojing; Chi,Xiaoyan; Zhang,Rijun.
This study aimed at optimizing the medium of a new Ganoderma lucidum strain CAU5501 to enhance the yield of exopolysaccharides (EPS) and mycelial growth. Firstly, the suitable level of glucose, magnesium, phosphate and C/N ratio was determined by single factor experiment. Subsequently, the optimum concentrations of these medium components were investigated using the orthogonal matrix method. The results indicated that the higher levels of EPS were correlated with the level of cell growth when glucose concentration was studied (data no show). The optimum medium for EPS yield was found to be 70 g/l glucose, 5 C/N ratio, 2.5 g/l KH2PO4, 0.75 g/l MgSO4·7H2O, and for mycelial growth was 50 g/l glucose, 5 C/N ratio, 1.5 g/l KH2PO4, 0.5 g/l MgSO4·7H2O. When...
Tipo: Info:eu-repo/semantics/article
Palavras-chave: Optimization; Exopolysaccharides; Ganoderma lucidum; Orthogonal matrix method; Submerged culture.
Ano: 2012
URL: http://www.scielo.br/scielo.php?script=sci_arttext&pid=S1517-83822012000200009