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Yaacov Okon - One of the best experts on this subject based on the ideXlab platform.
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Characterization of Genes Involved in Poly-β- Hydroxybutyrate Metabolism in Azospirillum brasilense
Symbiosis, 2020Co-Authors: Zohar Edelshtein, Jos Vanderleyden, Daniel Kadouri, Edouard Jurkevitch, Ann Vande Broek, Yaacov OkonAbstract:Under suboptimal growth conditions and like many other prokaryotes, rhizobacteria of the genus Azospirillum produce high levels of poly-βhydroxybutyrate (PHB). The two genes, bdhA (3-hydroxybutyrate dehydrogenase) and acsA2 (acetoacetyl-CoA synthetase), which are considered to be involved in the PHB degradation pathway in Azospirillum brasilense strain Sp7, were identified, cloned, and sequenced. Additionally, the expression of the bacterial genes phbA (βketothiolase) and phbC (PHB synthase), which are involved in PHB biosynthesis and the expression of the acsA2 gene, were studied using GUS fusions. Our results indicate that these genes are constitutively expressed in Azospirillum brasilense Sp7 and that the Ntr, PII and PZ nitrogen regulatory systems, which have been shown to be involved in the regulation of PHB synthesis, do not affect the expression of these genes. Expression of these genes is also shown to occur during association of A. brasilense with wheat roots.
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key physiological properties contributing to rhizosphere adaptation and plant growth promotion abilities of Azospirillum brasilense
Fems Microbiology Letters, 2012Co-Authors: Sharon Fibachpaldi, Saul Burdman, Yaacov OkonAbstract:Azospirillum brasilense is a plant growth promoting rhizobacterium (PGPR) that is being increasingly used in agriculture in a commercial scale. Recent research has elucidated key properties of A. brasilense that contribute to its ability to adapt to the rhizosphere habitat and to promote plant growth. They include synthesis of the auxin indole-3-acetic acid, nitric oxide, carotenoids, and a range of cell surface components as well as the ability to undergo phenotypic variation. Storage and utilization of polybetahydroxyalkanoate polymers are important for the shelf life of the bacteria in production of inoculants, products containing bacterial cells in a suitable carrier for agricultural use. Azospirillum brasilense is able to fix nitrogen, but despite some controversy, as judging from most systems evaluated so far, contribution of fixed nitrogen by this bacterium does not seem to play a major role in plant growth promotion. In this review, we focus on recent advances in the understanding of physiological properties of A . brasilense that are important for rhizosphere performance and successful interactions with plant roots.
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effect of Azospirillum brasilense coinoculated with rhizobium on phaseolus vulgaris flavonoids and nod factor production under salt stress
Soil Biology & Biochemistry, 2008Co-Authors: Marta S Dardanelli, Yaacov Okon, Francisco Fernandez J De Cordoba, Rosario M Espuny, Miguel Angel Rodriguez Carvajal, Maria Soria E Diaz, Antonio Miguel Gil Serrano, Manuel MegiasAbstract:The effects of salt upon Azospirillum brasilense strain Cd on plant growth, nodulation, flavonoid and lipochitooligosaccharide (LCOs-Nod factor) production, were sequentially followed after 4, 7 and 14 days during a Rhizobium-Phaseolus vulgaris cv. Negro Jamapa interaction, in a hydroponics growth system. Azospirillum brasilense promoted root branching in bean seedling roots and increased secretion of nod-gene-inducing flavonoid species, as detected by high-performance liquid chromatography (HPLC). The results also support that A. brasilense allows a longer, more persistent exudation of flavonoids by bean roots. A general positive effect of Azospirillum-Rhizobium coinoculation on the expression of nod-genes by Rhizobium tropici CIAT899 and Rhizobium etli ISP42, and on nodulation factor patterns, was observed in the presence of root exudates. The negative effects obtained under salt stress on nod-gene expression and on Nod factors' appearance were relieved in coinoculated plants.
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Identification and characterization of a periplasmic nitrate reductase in Azospirillum brasilense Sp245.
Archives of Microbiology, 2001Co-Authors: Oda Steenhoudt, Yaacov Okon, Veerle Keijers, Jos VanderleydenAbstract:The Azospirillum brasilense Sp245 napABC genes, encoding nitrate reductase activity, were isolated and sequenced. The derived protein sequences are very similar throughout the whole Nap segment to the NapABC protein sequences of Escherichia coli, Pseudomonas sp. G-179, Ralstonia eutropha, Rhodobacter sphaeroides, and Paracoccus denitrificans. Based on whole-cell nitrate reductase assays with the artificial electron donors benzyl viologen and methyl viologen, and assays with periplasmic cell-free extracts, it was concluded that the napABC-encoded enzyme activity in Azospirillum brasilense Sp245 corresponds to a periplasmic dissimilatory nitrate reductase, which was expressed under anoxic conditions and oxic conditions. A kanamycin-resistant Azospirillum brasilense Sp245 napA insertion mutant was constructed. The mutant still expressed assimilatory nitrate reductase activity, but was devoid of its periplasmic dissimilatory nitrate reductase activity.
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Polyhydroxyalkanoate analysis in Azospirillum brasilense
Canadian Journal of Microbiology, 1995Co-Authors: Robin Itzigsohn, Oded Yarden, Yaacov OkonAbstract:The considerable industrial interest in the qualitative and quantitative production of polyhydroxyalkanoates in microorganisms has led to the characterization of those synthesized in the nitrogen-fixing bacteria Azospirillum brasilense and Azotobacter paspali. In contrast to some other bacterial species, Azospirillum brasilense does not produce copolymers of hydroxyalkanoates when grown under the different carbon sources assayed, namely n-alkanoic acids, hydroxyalkanoates, and sugars with varying C:N ratios. Rather, only homopolymers of polyhydroxybutyrate were detected, comprising up to 70% of the cell dry mass. No copolymers were detected in Azotobacter paspali. Quantitative analyses of poly(β-hydroxybutyrate) are also presented.Key words: Azospirillum spp., Azotobacter paspali, polyhydroxyalkanoate analysis, PHA, PHB.
Jos Vanderleyden - One of the best experts on this subject based on the ideXlab platform.
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Characterization of Genes Involved in Poly-β- Hydroxybutyrate Metabolism in Azospirillum brasilense
Symbiosis, 2020Co-Authors: Zohar Edelshtein, Jos Vanderleyden, Daniel Kadouri, Edouard Jurkevitch, Ann Vande Broek, Yaacov OkonAbstract:Under suboptimal growth conditions and like many other prokaryotes, rhizobacteria of the genus Azospirillum produce high levels of poly-βhydroxybutyrate (PHB). The two genes, bdhA (3-hydroxybutyrate dehydrogenase) and acsA2 (acetoacetyl-CoA synthetase), which are considered to be involved in the PHB degradation pathway in Azospirillum brasilense strain Sp7, were identified, cloned, and sequenced. Additionally, the expression of the bacterial genes phbA (βketothiolase) and phbC (PHB synthase), which are involved in PHB biosynthesis and the expression of the acsA2 gene, were studied using GUS fusions. Our results indicate that these genes are constitutively expressed in Azospirillum brasilense Sp7 and that the Ntr, PII and PZ nitrogen regulatory systems, which have been shown to be involved in the regulation of PHB synthesis, do not affect the expression of these genes. Expression of these genes is also shown to occur during association of A. brasilense with wheat roots.
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The nodPQ genes in Azospirillum brasilense Sp7 are involved in sulfation of lipopolysaccharides.
Environmental Microbiology, 2005Co-Authors: Els Vanbleu, Biswa Choudhury, Russell W. Carlson, Jos VanderleydenAbstract:Summary Here we report on the presence of sulfated lipopolysaccharide molecules in Azospirillum brasilense, a plant growth-promoting rhizosphere bacterium. Chemical analysis provided structural data on the O-antigen composition and demonstrated the possible involvement of the nodPQ genes in O-antigen sulfation.
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Identification and characterization of a periplasmic nitrate reductase in Azospirillum brasilense Sp245.
Archives of Microbiology, 2001Co-Authors: Oda Steenhoudt, Yaacov Okon, Veerle Keijers, Jos VanderleydenAbstract:The Azospirillum brasilense Sp245 napABC genes, encoding nitrate reductase activity, were isolated and sequenced. The derived protein sequences are very similar throughout the whole Nap segment to the NapABC protein sequences of Escherichia coli, Pseudomonas sp. G-179, Ralstonia eutropha, Rhodobacter sphaeroides, and Paracoccus denitrificans. Based on whole-cell nitrate reductase assays with the artificial electron donors benzyl viologen and methyl viologen, and assays with periplasmic cell-free extracts, it was concluded that the napABC-encoded enzyme activity in Azospirillum brasilense Sp245 corresponds to a periplasmic dissimilatory nitrate reductase, which was expressed under anoxic conditions and oxic conditions. A kanamycin-resistant Azospirillum brasilense Sp245 napA insertion mutant was constructed. The mutant still expressed assimilatory nitrate reductase activity, but was devoid of its periplasmic dissimilatory nitrate reductase activity.
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Identification of the Structural Gene of A Periplasmic Nitrate Reductase of Azospirillum brasilense Sp245
Biological Nitrogen Fixation for the 21st Century, 1998Co-Authors: Oda Steenhoudt, Veerle Keijers, Jos VanderleydenAbstract:The wild-type strain Sp245 of Azospirillum brasilense expresses assimilatory and dissimilatory nitrate reducing activities (Hartmann, Zimmer, 1994), presumably catalysed by two different nitrate reductase enzyme complexes. The first enzyme allows the bacterium to use nitrate as sole source of nitrogen. The latter enzyme makes anaerobic growth with nitrate as terminal electron acceptor possible. Recently, we obtained genetic evidence for the presence of a third type of nitrate reductase in Azospirillum brasilense Sp245.
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Cloning and sequencing of the putative Azospirillum brasilense gene encoding GTP cyclohydrolase II.
Gene, 1995Co-Authors: Els Van Bastelaere, Veerle Keijers, Jos VanderleydenAbstract:Abstract Sequence analysis of a fragment of Azospirillum brasilense DNA revealed the presence of a ribA homologue, of which the 3′ portion encodes a putative GTP cyclohydrolase II. The 5′ portion (approx. half of the ORF) does not show homology to any other sequence from the databases.
Marta S Dardanelli - One of the best experts on this subject based on the ideXlab platform.
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reorganization of Azospirillum brasilense cell membrane is mediated by lipid composition adjustment to maintain optimal fluidity during water deficit
Journal of Applied Microbiology, 2016Co-Authors: A Cesari, Natalia Soledad Paulucci, Maria Alicia Biasutti, Yanina Belen Reguera, L A Gallarato, Christopher Kilmurray, Marta S DardanelliAbstract:AIMS: We study the Azospirillum brasilense tolerance to water deficit and the dynamics of adaptive process at the level of the membrane. METHODS AND RESULTS: Azospirillum brasilense was exposed to polyethylene glycol (PEG) growth and PEG shock. Tolerance, phospholipids and fatty acid (FA) composition and membrane fluidity were determined. Azospirillum brasilense was able to grow in the presence of PEG; however, its viability was reduced. Cells grown with PEG showed membrane fluidity similar to those grown without, the lipid composition was modified, increasing phosphatidylcholine and decreasing phosphatidylethanolamine amounts. The unsaturation FAs degree was reduced. The dynamics of the adaptive response revealed a decrease in fluidity 20 min after the addition of PEG, indicating that the PEG has a fluidizing effect on the hydrophobic region of the cell membrane. Fluidity returned to initial values after 60 min of PEG exposure. CONCLUSION: Azospirillum brasilense is able to perceive osmotic changes by changing the membrane fluidity. This effect is offset by changes in the composition of membrane phospholipid and FA, contributing to the homeostasis of membrane fluidity under water deficit. SIGNIFICANCE AND IMPACT OF THE STUDY: This knowledge can be used to develop new Azospirillum brasilense formulations showing an adapted membrane to water deficit.
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effect of Azospirillum brasilense coinoculated with rhizobium on phaseolus vulgaris flavonoids and nod factor production under salt stress
Soil Biology & Biochemistry, 2008Co-Authors: Marta S Dardanelli, Yaacov Okon, Francisco Fernandez J De Cordoba, Rosario M Espuny, Miguel Angel Rodriguez Carvajal, Maria Soria E Diaz, Antonio Miguel Gil Serrano, Manuel MegiasAbstract:The effects of salt upon Azospirillum brasilense strain Cd on plant growth, nodulation, flavonoid and lipochitooligosaccharide (LCOs-Nod factor) production, were sequentially followed after 4, 7 and 14 days during a Rhizobium-Phaseolus vulgaris cv. Negro Jamapa interaction, in a hydroponics growth system. Azospirillum brasilense promoted root branching in bean seedling roots and increased secretion of nod-gene-inducing flavonoid species, as detected by high-performance liquid chromatography (HPLC). The results also support that A. brasilense allows a longer, more persistent exudation of flavonoids by bean roots. A general positive effect of Azospirillum-Rhizobium coinoculation on the expression of nod-genes by Rhizobium tropici CIAT899 and Rhizobium etli ISP42, and on nodulation factor patterns, was observed in the presence of root exudates. The negative effects obtained under salt stress on nod-gene expression and on Nod factors' appearance were relieved in coinoculated plants.
Manuel Megias - One of the best experts on this subject based on the ideXlab platform.
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effect of Azospirillum brasilense coinoculated with rhizobium on phaseolus vulgaris flavonoids and nod factor production under salt stress
Soil Biology & Biochemistry, 2008Co-Authors: Marta S Dardanelli, Yaacov Okon, Francisco Fernandez J De Cordoba, Rosario M Espuny, Miguel Angel Rodriguez Carvajal, Maria Soria E Diaz, Antonio Miguel Gil Serrano, Manuel MegiasAbstract:The effects of salt upon Azospirillum brasilense strain Cd on plant growth, nodulation, flavonoid and lipochitooligosaccharide (LCOs-Nod factor) production, were sequentially followed after 4, 7 and 14 days during a Rhizobium-Phaseolus vulgaris cv. Negro Jamapa interaction, in a hydroponics growth system. Azospirillum brasilense promoted root branching in bean seedling roots and increased secretion of nod-gene-inducing flavonoid species, as detected by high-performance liquid chromatography (HPLC). The results also support that A. brasilense allows a longer, more persistent exudation of flavonoids by bean roots. A general positive effect of Azospirillum-Rhizobium coinoculation on the expression of nod-genes by Rhizobium tropici CIAT899 and Rhizobium etli ISP42, and on nodulation factor patterns, was observed in the presence of root exudates. The negative effects obtained under salt stress on nod-gene expression and on Nod factors' appearance were relieved in coinoculated plants.
Gladys Mori - One of the best experts on this subject based on the ideXlab platform.
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Saline stress affects the attachment of Azospirillum brasilense Cd to maize and wheat roots
Canadian Journal of Microbiology, 1998Co-Authors: Edgardo Jofré, Viviana Rivarola, Héctor Balegno, Sonia Fischer, Gladys MoriAbstract:The present work was designed to study the effect of saline stress on the attachment of Azospirillum brasilense to maize and wheat roots. We demonstrate that both attachment steps (adsorption and a...
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Response of Azospirillum brasilense Cd to sodium chloride stress.
Antonie Van Leeuwenhoek International Journal of General and Molecular Microbiology, 1998Co-Authors: Viviana Rivarola, Edgardo Jofré, Gladys Mori, Stella Castro, Adriana Fabra, Rosana Garnica, Héctor BalegnoAbstract:Growth of Azospirillum brasilense Cd in the presence of different NaCl concentrations showed that it tolerates up to 200 mM NaCl in the medium, without appreciable decline in growth rate. At 300 mM NaCl, a decrease of 66% in growth was observed at 24 h of culture. At 48 h of culture, bacteria in the presence of 300 mM NaCl reached the maximum optical density value that was attained at 12 h by control cultures. This investigation was designed to elucidate the effect of saline stress on Azospirillum brasilense Cd and the physiologic mechanism involved in its possible salinity tolerance. For this reason, studies of other osmolytes, as well as of putrescine metabolism and protein patterns were done with bacteria grown with this NaCl concentration in the medium, at 24 and at 48 hours. A. brasilense responded to saline stress elevating the intracellular concentration of glutamate at 24 h, and of K+at 48 h. Glucan pattern, putrescine metabolism, and total and periplasmic protein patterns of the treated group showed several changes with respect to the control. In spite of the several cellular functions affected by saline stress, the results imply that A. brasilense Cd shows salinity tolerance in these experimental conditions.
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Characterization of 2,4-dichlorophenoxyacetic acid transport and its relationship with polyamines in Azospirillum brasilense
Toxicology Letters, 1996Co-Authors: Stella Castro, Gladys Mori, Adriana Fabra, Viviana Rivarola, Walter Giordano, Héctor BalegnoAbstract:We have previously shown that 2,4-dichlorophenoxyacetic acid (2,4-D) inhibits Azospirillum brasilense growth, the synthesis of DNA, RNA and proteins. These toxic effects are prevented when polyamines are added to the culture medium. The purposes of our research were to determine the effects of the herbicide on the number of viable Azospirillum brasilense cells, characterize the 2,4-D transport system and to study the effects of polyamines upon the latter in this microorganism. We found that 2,4-D reduced the number of viable cells and that 2,4-D transport is energy-independent, since it was not affected by metabolic inhibitors. Polyamines did not alter 2,4-D uptake, further supporting the hypothesis that the herbicide most likely produces its toxic effects by interfering with the polyamine metabolism.
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2,4-Dichlorophenoxyacetic acid affects the attachment of Azospirillum brasilense Cd to maize roots
Toxicology, 1996Co-Authors: Edgardo Jofré, Gladys Mori, Stella Castro, Adriana Fabra, Viviana Rivarola, Héctor BalegnoAbstract:Abstract 2,4-Dichlorophenoxyacetic acid (2,4-D) is a herbicide widely applied to forage, grain and cereals. We previously determined that 1 mM 2,4-D diminished cell growth and cellular activity of Azospirillum brasilense Cd. The present work was designed to determine the possible effect of this herbicide—at concentrations used on crops—on the attachment of the bacteria to maize roots, since this step is of prime importance for the growth stimulation of the plant obtained with Azospirillum brasilense. In this paper we demonstrate that 2,4-D alters the bacterial adhesion to maize roots.
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In vitro protein synthesis is affected by the herbicide 2,4-dichlorophenoxyacetic acid in Azospirillum brasilense.
Toxicology, 1992Co-Authors: Viviana Rivarola, Gladys Mori, Adriana Fabra, Héctor BalegnoAbstract:The effects of 2,4-dichlorophenoxyacetic acid (2,4-D) on growth and protein, DNA and RNA synthesis of Azospirillum brasilense Cd were studied. At a concentration of 1 mM, 2,4-D inhibited cell growth, an effect that was reversed either by transferring bacteria to a control (2,4-D-free) medium or to a 2,4-D-treated medium supplemented with polyamines. The herbicide also affected in vitro protein synthesis, either when Azospirillum brasilense Cd's own cellular mRNA or an artificial mRNA was used. This effect was also reversed by the addition of polyamines to the 2,4-D-treated medium. Similar results were observed when DNA synthesis was studied in synchronous cultures. Taking into account the effects of this herbicide on animal cells (V.A. Rivarola and H.F. Balegno, Toxicology, 68 (1991) 109) we postulate that the mechanism of action of 2,4-D is similar on both procaryotic and eucaryotic cells, probably acting through the polyamine metabolism.
