The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform
Enrique Flores - One of the best experts on this subject based on the ideXlab platform.
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a major facilitator superfamily protein hepp is involved in formation of the heterocyst envelope polysaccharide in the cyanobacterium anabaena sp strain pcc 7120
Journal of Bacteriology, 2012Co-Authors: Rocio Lopezigual, Enrique Flores, Antonia Herrero, Sigal Lechnoyossef, Qing Fan, Peter C WolkAbstract:Some filamentous cyanobacteria such as Anabaena sp. strain PCC 7120 produce cells, termed heterocysts, specialized in Nitrogen fixation. Heterocysts bear a thick envelope containing an inner layer of glycolipids and an outer layer of polysaccharide that restrict the diffusion of air (including O2) into the heterocyst. Anabaena sp. mutants impaired in production of either of those layers show a Fox− phenotype (requiring fixed Nitrogen for growth under oxic conditions). We have characterized a set of transposon-induced Fox− mutants in which transposon Tn5-1063 was inserted into the Anabaena sp. chromosome open reading frame all1711 which encodes a predicted membrane protein that belongs to the major facilitator superfamily (MFS). These mutants showed higher Nitrogenase activities under anoxic than under oxic conditions and altered sucrose uptake. Electron microscopy and alcian blue staining showed a lack of the heterocyst envelope polysaccharide (Hep) layer. Northern blot and primer extension analyses showed that, in a manner dependent on the Nitrogen-Control transcription factor NtcA, all1711 was strongly induced after Nitrogen step-down. Confocal microscopy of an Anabaena sp. strain producing an All1711-green fluorescent protein (All1711-GFP) fusion protein showed induction in all cells of the filament but at higher levels in differentiating heterocysts. All1711-GFP was located in the periphery of the cells, consistent with All1711 being a cytoplasmic membrane protein. Expression of all1711 from the PglnA promoter in a multicopy plasmid led to production of a presumptive exopolysaccharide by vegetative cells. These results suggest that All1711, which we denote HepP, is involved in transport of glycoside(s), with a specific physiological role in production of Hep.
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Nitrogen assimilation and Nitrogen Control in cyanobacteria
Biochemical Society Transactions, 2005Co-Authors: Enrique Flores, Antonia HerreroAbstract:Nitrogen sources commonly used by cyanobacteria include ammonium, nitrate, nitrite, urea and atmospheric N2, and some cyanobacteria can also assimilate arginine or glutamine. ABC (ATP-binding cassette)-type permeases are involved in the uptake of nitrate/nitrite, urea and most amino acids, whereas secondary transporters take up ammonium and, in some strains, nitrate/nitrite. In cyanobacteria, nitrate and nitrite reductases are ferredoxin-dependent enzymes, arginine is catabolized by a combination of the urea cycle and arginase pathway, and urea is degraded by a Ni2+-dependent urease. These pathways provide ammonium that is incorporated into carbon skeletons through the glutamine synthetase–glutamate synthase cycle, in which 2-oxoglutarate is the final Nitrogen acceptor. The expression of many Nitrogen assimilation genes is subjected to regulation being activated by the Nitrogen-Control transcription factor NtcA, which is autoregulatory and whose activity appears to be influenced by 2-oxoglutarate and the signal transduction protein PII. In some filamentous cyanobacteria, N2 fixation takes place in specialized cells called heterocysts that differentiate from vegetative cells in a process strictly Controlled by NtcA. Abbreviations: ABC, ATP-binding cassette; CAP, catabolite gene activator protein
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cellular differentiation and the ntca transcription factor in filamentous cyanobacteria
Fems Microbiology Reviews, 2004Co-Authors: Antonia Herrero, Ana Valladares, Alicia M Muropastor, Enrique FloresAbstract:Some filamentous cyanobacteria can undergo a variety of cellular differentiation processes that permit their better adaptation to certain environmental conditions. These processes include the differentiation of hormogonia, short filaments aimed at the dispersal of the organism in the environment, of akinetes, cells resistant to various stress conditions, and of heterocysts, cells specialized in the fixation of atmospheric Nitrogen in oxic environments. NtcA is a transcriptional regulator that operates global Nitrogen Control in cyanobacteria by activating (and in some cases repressing) many genes involved in Nitrogen assimilation. NtcA is required for the triggering of heterocyst differentiation and for subsequent steps of its development and function. This requirement is based on the role of NtcA as an activator of the expression of hetR and other multiple genes at specific steps of the differentiation process. The products of these genes effect development as well as the distinct metabolism of the mature heterocyst. The different features found in the NtcA-dependent promoters, together with the cellular level of active NtcA protein, should have a role in the determination of the hierarchy of gene activation during the process of heterocyst differentiation.
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Nitrogen regulated genes for the metabolism of cyanophycin a bacterial Nitrogen reserve polymer expression and mutational analysis of two cyanophycin synthetase and cyanophycinase gene clusters in the heterocyst forming cyanobacterium anabaena sp pcc
Journal of Biological Chemistry, 2004Co-Authors: Silvia Picossi, Enrique Flores, Ana Valladares, Antonia HerreroAbstract:Two gene clusters each encoding the cyanophycin-metabolism enzymes cyanophycin synthetase and cyanophycinase are found in the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120. In cluster cph1, the genes cphB1 and cphA1 were expressed in media containing ammonium, nitrate, or N2 as Nitrogen sources, but expression was higher in the absence of combined Nitrogen taking place both in vegetative cells and heterocysts. Both genes were cotranscribed from three putative promoters located upstream of cphB1, and, additionally, the cphA1 gene was expressed monocistronically from at least two promoters located in the intergenic cphB1-cphA1 region. Both constitutive promoters and promoters dependent on the global Nitrogen Control transcriptional regulator NtcA were identified. In cluster cph2, the cphB2 and cphA2 genes, which are found in opposite orientations, were expressed as monocistronic messages in media containing ammonium, nitrate, or N2, but expression was higher in the absence of ammonium. Expression of the cph2 genes was lower than that of cph1 genes. Analysis of cph gene insertional mutants indicated that cluster cph1 genes contributed more than cluster cph2 genes to cyanophycin accumulation in the whole filament as well as in heterocysts. Diazotrophic growth was more severely impaired in cyanophycinase than in cyanophycin synthetase mutants, indicating that cyanophycin, although normally synthesized in the heterocysts, is not required for heterocyst function and that the inability to degrade this polymer is detrimental for the diazotrophic growth of the cyanobacterium.
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Nitrogen regulated group 2 sigma factor from synechocystis sp strain pcc 6803 involved in survival under Nitrogen stress
Journal of Bacteriology, 2001Co-Authors: Alicia M Muropastor, Antonia Herrero, Enrique FloresAbstract:The expression of sll1689, an open reading frame from the cyanobacterium Synechocystis sp. strain PCC 6803 putatively encoding a member of the ς70 family of sigma factors, appears to be regulated by the Nitrogen Control transcription factor NtcA. Disruption of sll1689 had no noticeable effect on exponential growth, identifying its product as a member of the group 2, nonessential class of ς70-like sigma factors; however, this disruption decreased the viability of the cells after long periods of Nitrogen starvation. We have named this gene rpoD2-V. The expression of glnN, encoding a type III glutamine synthetase, was impaired in strains bearing an inactivated copy of the rpoD2-V gene.
Antonia Herrero - One of the best experts on this subject based on the ideXlab platform.
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a major facilitator superfamily protein hepp is involved in formation of the heterocyst envelope polysaccharide in the cyanobacterium anabaena sp strain pcc 7120
Journal of Bacteriology, 2012Co-Authors: Rocio Lopezigual, Enrique Flores, Antonia Herrero, Sigal Lechnoyossef, Qing Fan, Peter C WolkAbstract:Some filamentous cyanobacteria such as Anabaena sp. strain PCC 7120 produce cells, termed heterocysts, specialized in Nitrogen fixation. Heterocysts bear a thick envelope containing an inner layer of glycolipids and an outer layer of polysaccharide that restrict the diffusion of air (including O2) into the heterocyst. Anabaena sp. mutants impaired in production of either of those layers show a Fox− phenotype (requiring fixed Nitrogen for growth under oxic conditions). We have characterized a set of transposon-induced Fox− mutants in which transposon Tn5-1063 was inserted into the Anabaena sp. chromosome open reading frame all1711 which encodes a predicted membrane protein that belongs to the major facilitator superfamily (MFS). These mutants showed higher Nitrogenase activities under anoxic than under oxic conditions and altered sucrose uptake. Electron microscopy and alcian blue staining showed a lack of the heterocyst envelope polysaccharide (Hep) layer. Northern blot and primer extension analyses showed that, in a manner dependent on the Nitrogen-Control transcription factor NtcA, all1711 was strongly induced after Nitrogen step-down. Confocal microscopy of an Anabaena sp. strain producing an All1711-green fluorescent protein (All1711-GFP) fusion protein showed induction in all cells of the filament but at higher levels in differentiating heterocysts. All1711-GFP was located in the periphery of the cells, consistent with All1711 being a cytoplasmic membrane protein. Expression of all1711 from the PglnA promoter in a multicopy plasmid led to production of a presumptive exopolysaccharide by vegetative cells. These results suggest that All1711, which we denote HepP, is involved in transport of glycoside(s), with a specific physiological role in production of Hep.
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Nitrogen assimilation and Nitrogen Control in cyanobacteria
Biochemical Society Transactions, 2005Co-Authors: Enrique Flores, Antonia HerreroAbstract:Nitrogen sources commonly used by cyanobacteria include ammonium, nitrate, nitrite, urea and atmospheric N2, and some cyanobacteria can also assimilate arginine or glutamine. ABC (ATP-binding cassette)-type permeases are involved in the uptake of nitrate/nitrite, urea and most amino acids, whereas secondary transporters take up ammonium and, in some strains, nitrate/nitrite. In cyanobacteria, nitrate and nitrite reductases are ferredoxin-dependent enzymes, arginine is catabolized by a combination of the urea cycle and arginase pathway, and urea is degraded by a Ni2+-dependent urease. These pathways provide ammonium that is incorporated into carbon skeletons through the glutamine synthetase–glutamate synthase cycle, in which 2-oxoglutarate is the final Nitrogen acceptor. The expression of many Nitrogen assimilation genes is subjected to regulation being activated by the Nitrogen-Control transcription factor NtcA, which is autoregulatory and whose activity appears to be influenced by 2-oxoglutarate and the signal transduction protein PII. In some filamentous cyanobacteria, N2 fixation takes place in specialized cells called heterocysts that differentiate from vegetative cells in a process strictly Controlled by NtcA. Abbreviations: ABC, ATP-binding cassette; CAP, catabolite gene activator protein
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cellular differentiation and the ntca transcription factor in filamentous cyanobacteria
Fems Microbiology Reviews, 2004Co-Authors: Antonia Herrero, Ana Valladares, Alicia M Muropastor, Enrique FloresAbstract:Some filamentous cyanobacteria can undergo a variety of cellular differentiation processes that permit their better adaptation to certain environmental conditions. These processes include the differentiation of hormogonia, short filaments aimed at the dispersal of the organism in the environment, of akinetes, cells resistant to various stress conditions, and of heterocysts, cells specialized in the fixation of atmospheric Nitrogen in oxic environments. NtcA is a transcriptional regulator that operates global Nitrogen Control in cyanobacteria by activating (and in some cases repressing) many genes involved in Nitrogen assimilation. NtcA is required for the triggering of heterocyst differentiation and for subsequent steps of its development and function. This requirement is based on the role of NtcA as an activator of the expression of hetR and other multiple genes at specific steps of the differentiation process. The products of these genes effect development as well as the distinct metabolism of the mature heterocyst. The different features found in the NtcA-dependent promoters, together with the cellular level of active NtcA protein, should have a role in the determination of the hierarchy of gene activation during the process of heterocyst differentiation.
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Nitrogen regulated genes for the metabolism of cyanophycin a bacterial Nitrogen reserve polymer expression and mutational analysis of two cyanophycin synthetase and cyanophycinase gene clusters in the heterocyst forming cyanobacterium anabaena sp pcc
Journal of Biological Chemistry, 2004Co-Authors: Silvia Picossi, Enrique Flores, Ana Valladares, Antonia HerreroAbstract:Two gene clusters each encoding the cyanophycin-metabolism enzymes cyanophycin synthetase and cyanophycinase are found in the heterocyst-forming cyanobacterium Anabaena sp. PCC 7120. In cluster cph1, the genes cphB1 and cphA1 were expressed in media containing ammonium, nitrate, or N2 as Nitrogen sources, but expression was higher in the absence of combined Nitrogen taking place both in vegetative cells and heterocysts. Both genes were cotranscribed from three putative promoters located upstream of cphB1, and, additionally, the cphA1 gene was expressed monocistronically from at least two promoters located in the intergenic cphB1-cphA1 region. Both constitutive promoters and promoters dependent on the global Nitrogen Control transcriptional regulator NtcA were identified. In cluster cph2, the cphB2 and cphA2 genes, which are found in opposite orientations, were expressed as monocistronic messages in media containing ammonium, nitrate, or N2, but expression was higher in the absence of ammonium. Expression of the cph2 genes was lower than that of cph1 genes. Analysis of cph gene insertional mutants indicated that cluster cph1 genes contributed more than cluster cph2 genes to cyanophycin accumulation in the whole filament as well as in heterocysts. Diazotrophic growth was more severely impaired in cyanophycinase than in cyanophycin synthetase mutants, indicating that cyanophycin, although normally synthesized in the heterocysts, is not required for heterocyst function and that the inability to degrade this polymer is detrimental for the diazotrophic growth of the cyanobacterium.
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Nitrogen regulated group 2 sigma factor from synechocystis sp strain pcc 6803 involved in survival under Nitrogen stress
Journal of Bacteriology, 2001Co-Authors: Alicia M Muropastor, Antonia Herrero, Enrique FloresAbstract:The expression of sll1689, an open reading frame from the cyanobacterium Synechocystis sp. strain PCC 6803 putatively encoding a member of the ς70 family of sigma factors, appears to be regulated by the Nitrogen Control transcription factor NtcA. Disruption of sll1689 had no noticeable effect on exponential growth, identifying its product as a member of the group 2, nonessential class of ς70-like sigma factors; however, this disruption decreased the viability of the cells after long periods of Nitrogen starvation. We have named this gene rpoD2-V. The expression of glnN, encoding a type III glutamine synthetase, was impaired in strains bearing an inactivated copy of the rpoD2-V gene.
Eduardo Santero - One of the best experts on this subject based on the ideXlab platform.
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distinct roles for ntrc and glnk in Nitrogen regulation of the pseudomonas sp strain adp cyanuric acid utilization operon
Fems Microbiology Letters, 2009Co-Authors: Vicente Garciagonzalez, Eduardo Santero, Alicia Jimenezfernandez, Ana B Hervas, Ines Canosa, Fernando GovantesAbstract:The Pseudomonas sp. strain ADP atzDEF operon encodes the enzymes involved in cyanuric acid mineralization, the final stage of the s-triazine herbicide atrazine degradative pathway. We have previously shown that atzDEF is under Nitrogen Control in both its natural host and Pseudomonas putida KT2442. Expression of atzDEF requires the divergently encoded LysR-type transcriptional regulator AtzR. Here, we take advantage of the poor induction of atzDEF in Escherichia coli to identify Pseudomonas factors involved in Nitrogen Control of atzDEF expression. Simultaneous production of P. putida NtrC and GlnK, along with AtzR, restored the normal atzDEF regulatory pattern. Gene expression analysis in E. coli and P. putida indicated that NtrC activates atzR expression, while the role of GlnK is to promote AtzR activation of atzDEF under Nitrogen limitation. Activation of atzDEF in a mutant background deficient in GlnK uridylylation suggests that post-translational modification is not strictly required for transduction of the Nitrogen limitation signal to AtzR. The present data and our previous results are integrated in a regulatory circuit that describes all the known responses of the atzDEF operon.
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Nitrogen Control of atrazine utilization in pseudomonas sp strain adp
Applied and Environmental Microbiology, 2003Co-Authors: Vicente Garciagonzalez, Fernando Govantes, Richard G Burns, Liz J. Shaw, Eduardo SanteroAbstract:Pseudomonas sp. strain ADP uses the herbicide atrazine as the sole Nitrogen source. We have devised a simple atrazine degradation assay to determine the effect of other Nitrogen sources on the atrazine degradation pathway. The atrazine degradation rate was greatly decreased in cells grown on Nitrogen sources that support rapid growth of Pseudomonas sp. strain ADP compared to cells cultivated on growth-limiting Nitrogen sources. The presence of atrazine in addition to the Nitrogen sources did not stimulate degradation. High degradation rates obtained in the presence of ammonium plus the glutamine synthetase inhibitor MSX and also with an Nas- mutant derivative grown on nitrate suggest that Nitrogen regulation operates by sensing intracellular levels of some key Nitrogen-containing metabolite. Nitrate amendment in soil microcosms resulted in decreased atrazine mineralization by the wild-type strain but not by the Nas- mutant. This suggests that, although Nitrogen repression of the atrazine catabolic pathway may have a strong impact on atrazine biodegradation in Nitrogen-fertilized soils, the use of selected mutant variants may contribute to overcoming this limitation.
Vicente Garciagonzalez - One of the best experts on this subject based on the ideXlab platform.
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distinct roles for ntrc and glnk in Nitrogen regulation of the pseudomonas sp strain adp cyanuric acid utilization operon
Fems Microbiology Letters, 2009Co-Authors: Vicente Garciagonzalez, Eduardo Santero, Alicia Jimenezfernandez, Ana B Hervas, Ines Canosa, Fernando GovantesAbstract:The Pseudomonas sp. strain ADP atzDEF operon encodes the enzymes involved in cyanuric acid mineralization, the final stage of the s-triazine herbicide atrazine degradative pathway. We have previously shown that atzDEF is under Nitrogen Control in both its natural host and Pseudomonas putida KT2442. Expression of atzDEF requires the divergently encoded LysR-type transcriptional regulator AtzR. Here, we take advantage of the poor induction of atzDEF in Escherichia coli to identify Pseudomonas factors involved in Nitrogen Control of atzDEF expression. Simultaneous production of P. putida NtrC and GlnK, along with AtzR, restored the normal atzDEF regulatory pattern. Gene expression analysis in E. coli and P. putida indicated that NtrC activates atzR expression, while the role of GlnK is to promote AtzR activation of atzDEF under Nitrogen limitation. Activation of atzDEF in a mutant background deficient in GlnK uridylylation suggests that post-translational modification is not strictly required for transduction of the Nitrogen limitation signal to AtzR. The present data and our previous results are integrated in a regulatory circuit that describes all the known responses of the atzDEF operon.
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Nitrogen Control of atrazine utilization in pseudomonas sp strain adp
Applied and Environmental Microbiology, 2003Co-Authors: Vicente Garciagonzalez, Fernando Govantes, Richard G Burns, Liz J. Shaw, Eduardo SanteroAbstract:Pseudomonas sp. strain ADP uses the herbicide atrazine as the sole Nitrogen source. We have devised a simple atrazine degradation assay to determine the effect of other Nitrogen sources on the atrazine degradation pathway. The atrazine degradation rate was greatly decreased in cells grown on Nitrogen sources that support rapid growth of Pseudomonas sp. strain ADP compared to cells cultivated on growth-limiting Nitrogen sources. The presence of atrazine in addition to the Nitrogen sources did not stimulate degradation. High degradation rates obtained in the presence of ammonium plus the glutamine synthetase inhibitor MSX and also with an Nas- mutant derivative grown on nitrate suggest that Nitrogen regulation operates by sensing intracellular levels of some key Nitrogen-containing metabolite. Nitrate amendment in soil microcosms resulted in decreased atrazine mineralization by the wild-type strain but not by the Nas- mutant. This suggests that, although Nitrogen repression of the atrazine catabolic pathway may have a strong impact on atrazine biodegradation in Nitrogen-fertilized soils, the use of selected mutant variants may contribute to overcoming this limitation.
Fernando Govantes - One of the best experts on this subject based on the ideXlab platform.
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distinct roles for ntrc and glnk in Nitrogen regulation of the pseudomonas sp strain adp cyanuric acid utilization operon
Fems Microbiology Letters, 2009Co-Authors: Vicente Garciagonzalez, Eduardo Santero, Alicia Jimenezfernandez, Ana B Hervas, Ines Canosa, Fernando GovantesAbstract:The Pseudomonas sp. strain ADP atzDEF operon encodes the enzymes involved in cyanuric acid mineralization, the final stage of the s-triazine herbicide atrazine degradative pathway. We have previously shown that atzDEF is under Nitrogen Control in both its natural host and Pseudomonas putida KT2442. Expression of atzDEF requires the divergently encoded LysR-type transcriptional regulator AtzR. Here, we take advantage of the poor induction of atzDEF in Escherichia coli to identify Pseudomonas factors involved in Nitrogen Control of atzDEF expression. Simultaneous production of P. putida NtrC and GlnK, along with AtzR, restored the normal atzDEF regulatory pattern. Gene expression analysis in E. coli and P. putida indicated that NtrC activates atzR expression, while the role of GlnK is to promote AtzR activation of atzDEF under Nitrogen limitation. Activation of atzDEF in a mutant background deficient in GlnK uridylylation suggests that post-translational modification is not strictly required for transduction of the Nitrogen limitation signal to AtzR. The present data and our previous results are integrated in a regulatory circuit that describes all the known responses of the atzDEF operon.
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Nitrogen Control of atrazine utilization in pseudomonas sp strain adp
Applied and Environmental Microbiology, 2003Co-Authors: Vicente Garciagonzalez, Fernando Govantes, Richard G Burns, Liz J. Shaw, Eduardo SanteroAbstract:Pseudomonas sp. strain ADP uses the herbicide atrazine as the sole Nitrogen source. We have devised a simple atrazine degradation assay to determine the effect of other Nitrogen sources on the atrazine degradation pathway. The atrazine degradation rate was greatly decreased in cells grown on Nitrogen sources that support rapid growth of Pseudomonas sp. strain ADP compared to cells cultivated on growth-limiting Nitrogen sources. The presence of atrazine in addition to the Nitrogen sources did not stimulate degradation. High degradation rates obtained in the presence of ammonium plus the glutamine synthetase inhibitor MSX and also with an Nas- mutant derivative grown on nitrate suggest that Nitrogen regulation operates by sensing intracellular levels of some key Nitrogen-containing metabolite. Nitrate amendment in soil microcosms resulted in decreased atrazine mineralization by the wild-type strain but not by the Nas- mutant. This suggests that, although Nitrogen repression of the atrazine catabolic pathway may have a strong impact on atrazine biodegradation in Nitrogen-fertilized soils, the use of selected mutant variants may contribute to overcoming this limitation.