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John R Gallon - One of the best experts on this subject based on the ideXlab platform.
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interrelationships between the pathways of inorganic nitrogen assimilation in the cyanobacterium Gloeothece can be described using a mechanistic mathematical model
New Phytologist, 2003Co-Authors: Nicholas Stephens, Kevin J Flynn, John R GallonAbstract:Summary • A mathematical model is described that simulates the major features of the interactions between different nitrogen (N)-sources in the nonheterocystous diazotrophic cyanobacterium Gloeothece. • The interaction between ammonium and nitrate is related to the intracellular concentration of glutamine (GLN), which in turn is representative of cellular N-status. Development of nitrogenase activity is related to N-limitation but, once developed, continues for as long as there is sufficient glucan (carbon-reserve) in order to support N2 fixation and the assimilation of the resultant ammonium into amino acids. • Nitrogenase activity decreases in response to elevated N-status and also to increased net oxygen evolution, in keeping with biochemical reality. The model describes the diel cycle of C and N2 fixation as seen under alternating 12 h light and 12 h darkness, and also the N2 fixation cycle of about 40 h duration seen in cells cultured in continuous illumination. • This model has the potential to be adapted to describe N2 fixation in heterocystous cyanobacterium and in Trichodesmium.
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synthesis and proteolytic degradation of nitrogenase in cultures of the unicellular cyanobacterium Gloeothece strain atcc 27152
Microbiology, 1999Co-Authors: Lisa J Dougherty, John P H Reade, Lyndon J Rogers, John R GallonAbstract:In cultures of the unicellular cyanobacterium Gloeothece sp. ATCC 27152 growing under alternating 12 h light and 12 h darkness, nitrogenase activity appears as cultures enter the dark phase. Synthesis of both component proteins of nitrogenase commences immediately prior to the appearance of activity and continues until about 8 h into the period of darkness. The two components (Fe-protein and MoFe-protein) are synthesized in a molar ratio of about 3:1. Degradation of the nitrogenase proteins starts as early as 4 h into the dark period and increases markedly as cultures enter the light phase. As a result, both nitrogenase proteins are completely absent from cultures during most of the light phase. In contrast, all of the other proteins investigated appeared to be present throughout the cycle of alternating light and darkness. Degradation of nitrogenase depends upon protein synthesis during the last 6 h of darkness and is prevented by addition of protease inhibitors. Two proteins, of M(r) 47,000 and 29,000, are specifically synthesized during this period and it is possible that they have a role in nitrogenase degradation. Proteolytic activity of extracts of Gloeothece, measured as the ability to degrade azocasein, increased markedly during the early part of the light period, but this increase did not depend on protein synthesis. This activity does not therefore correspond to that specifically involved in nitrogenase catabolism, though it may act on initial breakdown products generated by a nitrogenase-specific degradative system. A phycobiliprotein appears to act as a temporary store of the degradation products of nitrogenase.
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effects of inorganic nitrogen compounds on the activity and synthesis of nitrogenase in Gloeothece nageli sp atcc 27152
New Phytologist, 1999Co-Authors: J Cheng, Charles R Hipkin, John R GallonAbstract:Addition of 2 mM nitrite or ammonium to aerobically incubated cultures of Gloeothece rapidly inhibited N2 fixation (measured as acetylene reduction). In contrast, 2 mM nitrate inhibited N2 fixation less rapidly and less extensively, and often temporarily stimulated nitrogenase activity. The inhibitory effects of both nitrate and ammonium could be prevented by addition of 3 mM L-methionine-DL-sulphoximine, suggesting that the true inhibitor of N2 fixation was an assimilatory product of ammonium rather than either ammonium or nitrate itself. The inhibition of N2 fixation by nitrite could not, however, be prevented by addition of L-methionine-DL- sulphoximine. On the other hand, nitrite (unlike nitrate and ammonium) did not inhibit N2 fixation in cultures incubated under a gas phase lacking oxygen. These findings suggest that the mechanism whereby nitrite inhibits N2 fixation in Gloeothece differs from that of either nitrate or ammonium. The inhibitory effect of nitrite on N2 fixation did not involve reduction of nitrite to nitric oxide, though nitric oxide was a potent inhibitor of nitrogenase activity in Gloeothece. Nitrate and nitrite inhibited the synthesis of nitrogenase in Gloeothece, while ammonium not only inhibited nitrogenase synthesis but also stimulated degradation of the enzyme. In addition, all three compounds favoured the appearance of the Fe-protein of nitrogenase in its larger, presumed inactive, form.
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modification of the fe protein of the nitrogenase of Gloeothece nageli sp atcc 27152 during growth under alternating light and darkness
New Phytologist, 1993Co-Authors: John R GallonAbstract:SUMMARY The Fe protein of the nitrogenase of the unicellular Cyanobacterium Gloeothece (Nageli) sp. ATCC 27152 can be resolved by SDS–PAGE into two antigenically detectable components of approximate Mr 38500 and 40000 respectively. The larger form of this protein may be produced by modification of the smaller form. Modification of the Fe protein is promoted under conditions where O2 (but not O2− or H2O2) has increased access to the enzyme, but does not allow nitrogenase to function under conditions of O2 stress. During growth of Gloeothece under alternating light and darkness, antigenically detectable Fe protein is absent throughout most of the light period. The restriction of nitrogenase activity to the period of darkness is better explained in terms of regulation of nitrogenase synthesis and degradation than by reversible modification of a constant intracellular concentration of Fe protein. However, newly synthesized Fe protein always appeared initially as its larger form, which may be catalytically inactive in aerobic cultures of Gloeothece. Conversion of this form to the smaller, assumed active, form of the Fe protein may be an additional factor in explaining the increase in nitrogenase activity that occurs during the first few hours of each dark phase.
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the effect of temperature on the sensitivity of nitrogenase to oxygen in the cyanobacteria anabaena cylindrica lemmermann and Gloeothece nageli
New Phytologist, 1993Co-Authors: John R Gallon, Dennis M Pederson, Geoffrey D SmithAbstract:SUMMARY Transient exposure to elevated temperature (37-40 °C) inhibited N2 fixation (acetylene reduction) in cultures of the heterocystous cyanobacterium Anabaena cylindrica (Lemmermann) ATCC 27899 and the unicellular, non-heterocystous cyanobacterium Gloeothece sp. (Nageli) ATCC 27152. In neither organism was inhibition of N2 fixation due to thermal inactivation of nitrogenase. Rather, inactivation of N2 fixation at elevated temperature was a consequence of increased sensitivity to inhibition by O2 In A. cylindrica, thermally induced inactivation of N2 fixation by O2 could be correlated with inhibition of uptake hydrogenase. However, in Gloeothece, inhibition of carbon-supported respiratory O2 consumption by elevated temperature was the probable cause of the increased sensitivity of N2 fixation to O2.
Paula Tamagnini - One of the best experts on this subject based on the ideXlab platform.
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itraq based quantitative proteomic analysis of Gloeothece sp pcc 6909 comparison with its sheathless mutant and adaptations to nitrate deficiency and sulfur limitation
Journal of Proteomics, 2011Co-Authors: S Pereira, Paula Tamagnini, Pedro Moradasferreira, Martin E Barriosllerena, Phillip C WrightAbstract:Gloeothece sp. PCC 6909 is a unicellular N(2)-fixing cyanobacterium with a well defined and highly developed sheath surrounding its cells. A sheathless mutant of this strain was previously obtained by chemical mutagenesis and, although lacking the sheath, it releases large amounts of polysaccharides into the culture medium. To provide a global understanding on the metabolic differences between the two phenotypes, the proteomes of the wild type and mutant were analyzed using a cross-species proteomics approach coupled with iTRAQ isobaric tagging technology, since their genome sequences are not yet available. Effects arising from the presence/absence of nitrate and sulfur are presented as two metabolically directed follow-up iTRAQ studies. These nutrients are believed to play a major role in Gloeothece's metabolism, including the production of extracellular polymeric substances - EPS. 454, 124, and 53 proteins were identified and reliably quantified using homology anchoring approaches for iTRAQ previously described. The results obtained strongly suggest that the chemical mutagenesis affected the regulation of a number of key cellular processes, as revealed by the significant fold changes observed for proteins covering a large spectrum of functional groups. Moreover, they provide new insights on the adaptations of Gloeothece cells to nitrate-deficiency and sulfur-limitation.
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sheathless mutant of cyanobacterium Gloeothece sp strain pcc 6909 with increased capacity to remove copper ions from aqueous solutions
Applied and Environmental Microbiology, 2008Co-Authors: Ernesto Micheletti, Paula Tamagnini, Pedro Moradasferreira, S Pereira, Francesca Mannelli, Roberto De PhilippisAbstract:Cyanobacteria are a large and widespread group of photoautotrophic microorganisms that combine the ability to perform an oxygenic plant-like photosynthesis with typical prokaryotic features (40). Outside their atypical gram-negative cell walls (15), many strains possess outermost structures, mainly of a polysaccharidic nature, that differ in thickness and consistency. These structures can be referred to as sheaths, capsules, and slimes (4). The term sheath is applied to the usually thin and electron-dense layer surrounding the cells or the cell groups; the capsule refers to the thick and gelatinous layer intimately associated with the cell surface and presenting sharp outlines, whereas the term slime is used to designate the mucilaginous material that is dispersed around the organism but does not reflect the shape of the cells. During cell growth, aliquots of these polysaccharides can be released into the surrounding medium (referred to as released exocellular polysaccharides [RPS]), causing a progressive increase in its viscosity (4). The cyanobacterial exopolysaccharides (EPSs; a general term which includes both the polysaccharidic structures that remain intimately associated with the cell, i.e., the sheath and capsule, and those released into the culture medium, i.e., the RPS) exhibit some typical characteristics that distinguish them from the polymers synthesized by other bacteria: they frequently contain two different uronic acids, they build a polymer particularly rich in negatively charged groups, they possess a larger number of different monosaccharides, which increases the number of possible conformations of the polymer, and they contain sulfate groups, a unique feature among prokaryotes and one that is shared by the EPSs produced by Archaea (5, 31). At present, heavy metals are one of the most widespread causes of pollution, and their continuous accumulation in water bodies and soils constitutes a serious hazard to both the environment and human health (11, 20). The use of EPS-producing microorganisms (or isolated EPSs) is a valid alternative to conventional chemical and physicochemical methods to remove metallic cations from polluted waters (35). This new technology presents advantages such as the use of natural and renewable sources, reduced costs, rapid kinetics of metal removal, the ability to remove metallic ions present at low concentrations, the possibility to treat contaminated waters simultaneously with several different metal ions, and the possibility of recovering valuable metals from the biosorbent (6, 18). In this context, EPS-producing cyanobacteria appear to be promising candidates due to the unique characteristics of their polysaccharidic envelopes (see above). The efficiency of cyanobacterial EPS in the removal of metal ions has been discussed previously, with an emphasis on the monosaccharidic composition of the polymer, the isolation of EPS, and the subsequent utilization with removal assays (5, 8, 21). Although the chemical composition of the sheaths of several cyanobacterial strains has been determined (14, 15, 32, 33, 38, 39) and the importance of the capsules and RPS in the metal-removal process has been recognized (6), information about the exact contribution of each type of EPSs and/or functional group to the biosorption of the metal is still very limited. This work aimed to understand the role of the various outermost polysaccharidic investments in the process of copper removal by the unicellular N2-fixing cyanobacterium Gloeothece sp. strain PCC 6909. This strain is characterized by a well-defined laminated sheath that encloses cells and cell groups, maintaining a firm colonial structure. In this study, both the wild-type and a sheathless mutant, previously obtained by chemical mutagenesis, were used to elucidate the contribution of each type of EPS to the metal-removal process. Moreover, chemical and physical analyses were performed to identify the major sites responsible for the metal binding.
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sheathless mutant of cyanobacterium Gloeothece sp strain pcc 6909 with increased capacity to remove copper ions from
2008Co-Authors: Ernesto Micheletti, Paula Tamagnini, Pedro Moradasferreira, S Pereira, Francesca Mannelli, Roberto De PhilippisAbstract:The cyanobacterium Gloeothece sp. strain PCC 6909 and its sheathless mutant were tested for their abilities to remove copper ions from aqueous solutions, with the aim of defining the role of the various outermost polysaccharidic investments in the removal of the metal ions. Microscopy studies and chemical analyses revealed that, although the mutant does not possess a sheath, it releases large amounts of polysaccharidic material (released exocellular polysaccharides [RPS]) into the culture medium. The RPS of the wild type and the mutant are composed of the same 11 sugars, although they are present in different amounts, and the RPS of the mutant possesses a larger amount of acidic sugars and a smaller amount of deoxysugars than the wild type. Unexpectedly, whole cultures of the mutant were more effective in the removal of the heavy metal than the wild type (46.3 3.1 and 26.7 1.5 mg of Cu 2 removed per g of dry weight, respectively). Moreover, we demonstrated that the contribution of the sheath to the metal-removal capacity of the wild type is scarce and that the RPS of the mutant is more efficient in removing copper. This suggests that the metal ions are preferably bound to the cell wall and to RPS functional groups rather than to the sheath. Therefore, the increased copper binding efficiency observed with the sheathless mutant can be attributed to the release of a polysaccharide containing larger amounts and/or more accessible functional groups (e.g., carboxyl and amide groups).
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characterization and transcriptional analysis of hupslw in Gloeothece sp atcc 27152 an uptake hydrogenase from a unicellular cyanobacterium
Microbiology, 2004Co-Authors: Paulo J Oliveira, Elsa Leitao, Paula Tamagnini, Pedro Moradasferreira, Fredrik OxelfeltAbstract:The structural genes (hupSL) encoding an uptake hydrogenase in the unicellular cyanobacterium Gloeothece sp. ATCC 27152, a strain capable of aerobic N2 fixation, were identified and sequenced. 3′-RACE experiments uncovered the presence of an additional ORF 184 bp downstream of hupL, showing a high degree of sequence identity with a gene encoding an uptake-hydrogenase-specific endopeptidase (hupW) in other cyanobacteria. In addition, the transcription start point was identified 238 bp upstream of the hupS translational start. RT-PCR experiments revealed that hupW is co-transcribed with the uptake hydrogenase structural genes in Gloeothece sp. ATCC 27152. In addition, Northern hybridizations clearly showed that hupSLW are transcribed under nitrogen fixing conditions, but not in the presence of combined nitrogen. A putative NtcA binding site was identified in the promoter region upstream of hupS, centred at −41·5 bp with respect to the transcription start point. Electrophoretic retardation of a labelled DNA fragment (harbouring the putative NtcA-binding motif) was significantly affected by an Escherichia coli cell-free extract containing overexpressed NtcA, suggesting that NtcA is involved in the transcriptional regulation of hupSLW.
Pedro Moradasferreira - One of the best experts on this subject based on the ideXlab platform.
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itraq based quantitative proteomic analysis of Gloeothece sp pcc 6909 comparison with its sheathless mutant and adaptations to nitrate deficiency and sulfur limitation
Journal of Proteomics, 2011Co-Authors: S Pereira, Paula Tamagnini, Pedro Moradasferreira, Martin E Barriosllerena, Phillip C WrightAbstract:Gloeothece sp. PCC 6909 is a unicellular N(2)-fixing cyanobacterium with a well defined and highly developed sheath surrounding its cells. A sheathless mutant of this strain was previously obtained by chemical mutagenesis and, although lacking the sheath, it releases large amounts of polysaccharides into the culture medium. To provide a global understanding on the metabolic differences between the two phenotypes, the proteomes of the wild type and mutant were analyzed using a cross-species proteomics approach coupled with iTRAQ isobaric tagging technology, since their genome sequences are not yet available. Effects arising from the presence/absence of nitrate and sulfur are presented as two metabolically directed follow-up iTRAQ studies. These nutrients are believed to play a major role in Gloeothece's metabolism, including the production of extracellular polymeric substances - EPS. 454, 124, and 53 proteins were identified and reliably quantified using homology anchoring approaches for iTRAQ previously described. The results obtained strongly suggest that the chemical mutagenesis affected the regulation of a number of key cellular processes, as revealed by the significant fold changes observed for proteins covering a large spectrum of functional groups. Moreover, they provide new insights on the adaptations of Gloeothece cells to nitrate-deficiency and sulfur-limitation.
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sheathless mutant of cyanobacterium Gloeothece sp strain pcc 6909 with increased capacity to remove copper ions from aqueous solutions
Applied and Environmental Microbiology, 2008Co-Authors: Ernesto Micheletti, Paula Tamagnini, Pedro Moradasferreira, S Pereira, Francesca Mannelli, Roberto De PhilippisAbstract:Cyanobacteria are a large and widespread group of photoautotrophic microorganisms that combine the ability to perform an oxygenic plant-like photosynthesis with typical prokaryotic features (40). Outside their atypical gram-negative cell walls (15), many strains possess outermost structures, mainly of a polysaccharidic nature, that differ in thickness and consistency. These structures can be referred to as sheaths, capsules, and slimes (4). The term sheath is applied to the usually thin and electron-dense layer surrounding the cells or the cell groups; the capsule refers to the thick and gelatinous layer intimately associated with the cell surface and presenting sharp outlines, whereas the term slime is used to designate the mucilaginous material that is dispersed around the organism but does not reflect the shape of the cells. During cell growth, aliquots of these polysaccharides can be released into the surrounding medium (referred to as released exocellular polysaccharides [RPS]), causing a progressive increase in its viscosity (4). The cyanobacterial exopolysaccharides (EPSs; a general term which includes both the polysaccharidic structures that remain intimately associated with the cell, i.e., the sheath and capsule, and those released into the culture medium, i.e., the RPS) exhibit some typical characteristics that distinguish them from the polymers synthesized by other bacteria: they frequently contain two different uronic acids, they build a polymer particularly rich in negatively charged groups, they possess a larger number of different monosaccharides, which increases the number of possible conformations of the polymer, and they contain sulfate groups, a unique feature among prokaryotes and one that is shared by the EPSs produced by Archaea (5, 31). At present, heavy metals are one of the most widespread causes of pollution, and their continuous accumulation in water bodies and soils constitutes a serious hazard to both the environment and human health (11, 20). The use of EPS-producing microorganisms (or isolated EPSs) is a valid alternative to conventional chemical and physicochemical methods to remove metallic cations from polluted waters (35). This new technology presents advantages such as the use of natural and renewable sources, reduced costs, rapid kinetics of metal removal, the ability to remove metallic ions present at low concentrations, the possibility to treat contaminated waters simultaneously with several different metal ions, and the possibility of recovering valuable metals from the biosorbent (6, 18). In this context, EPS-producing cyanobacteria appear to be promising candidates due to the unique characteristics of their polysaccharidic envelopes (see above). The efficiency of cyanobacterial EPS in the removal of metal ions has been discussed previously, with an emphasis on the monosaccharidic composition of the polymer, the isolation of EPS, and the subsequent utilization with removal assays (5, 8, 21). Although the chemical composition of the sheaths of several cyanobacterial strains has been determined (14, 15, 32, 33, 38, 39) and the importance of the capsules and RPS in the metal-removal process has been recognized (6), information about the exact contribution of each type of EPSs and/or functional group to the biosorption of the metal is still very limited. This work aimed to understand the role of the various outermost polysaccharidic investments in the process of copper removal by the unicellular N2-fixing cyanobacterium Gloeothece sp. strain PCC 6909. This strain is characterized by a well-defined laminated sheath that encloses cells and cell groups, maintaining a firm colonial structure. In this study, both the wild-type and a sheathless mutant, previously obtained by chemical mutagenesis, were used to elucidate the contribution of each type of EPS to the metal-removal process. Moreover, chemical and physical analyses were performed to identify the major sites responsible for the metal binding.
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sheathless mutant of cyanobacterium Gloeothece sp strain pcc 6909 with increased capacity to remove copper ions from
2008Co-Authors: Ernesto Micheletti, Paula Tamagnini, Pedro Moradasferreira, S Pereira, Francesca Mannelli, Roberto De PhilippisAbstract:The cyanobacterium Gloeothece sp. strain PCC 6909 and its sheathless mutant were tested for their abilities to remove copper ions from aqueous solutions, with the aim of defining the role of the various outermost polysaccharidic investments in the removal of the metal ions. Microscopy studies and chemical analyses revealed that, although the mutant does not possess a sheath, it releases large amounts of polysaccharidic material (released exocellular polysaccharides [RPS]) into the culture medium. The RPS of the wild type and the mutant are composed of the same 11 sugars, although they are present in different amounts, and the RPS of the mutant possesses a larger amount of acidic sugars and a smaller amount of deoxysugars than the wild type. Unexpectedly, whole cultures of the mutant were more effective in the removal of the heavy metal than the wild type (46.3 3.1 and 26.7 1.5 mg of Cu 2 removed per g of dry weight, respectively). Moreover, we demonstrated that the contribution of the sheath to the metal-removal capacity of the wild type is scarce and that the RPS of the mutant is more efficient in removing copper. This suggests that the metal ions are preferably bound to the cell wall and to RPS functional groups rather than to the sheath. Therefore, the increased copper binding efficiency observed with the sheathless mutant can be attributed to the release of a polysaccharide containing larger amounts and/or more accessible functional groups (e.g., carboxyl and amide groups).
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characterization and transcriptional analysis of hupslw in Gloeothece sp atcc 27152 an uptake hydrogenase from a unicellular cyanobacterium
Microbiology, 2004Co-Authors: Paulo J Oliveira, Elsa Leitao, Paula Tamagnini, Pedro Moradasferreira, Fredrik OxelfeltAbstract:The structural genes (hupSL) encoding an uptake hydrogenase in the unicellular cyanobacterium Gloeothece sp. ATCC 27152, a strain capable of aerobic N2 fixation, were identified and sequenced. 3′-RACE experiments uncovered the presence of an additional ORF 184 bp downstream of hupL, showing a high degree of sequence identity with a gene encoding an uptake-hydrogenase-specific endopeptidase (hupW) in other cyanobacteria. In addition, the transcription start point was identified 238 bp upstream of the hupS translational start. RT-PCR experiments revealed that hupW is co-transcribed with the uptake hydrogenase structural genes in Gloeothece sp. ATCC 27152. In addition, Northern hybridizations clearly showed that hupSLW are transcribed under nitrogen fixing conditions, but not in the presence of combined nitrogen. A putative NtcA binding site was identified in the promoter region upstream of hupS, centred at −41·5 bp with respect to the transcription start point. Electrophoretic retardation of a labelled DNA fragment (harbouring the putative NtcA-binding motif) was significantly affected by an Escherichia coli cell-free extract containing overexpressed NtcA, suggesting that NtcA is involved in the transcriptional regulation of hupSLW.
S Pereira - One of the best experts on this subject based on the ideXlab platform.
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itraq based quantitative proteomic analysis of Gloeothece sp pcc 6909 comparison with its sheathless mutant and adaptations to nitrate deficiency and sulfur limitation
Journal of Proteomics, 2011Co-Authors: S Pereira, Paula Tamagnini, Pedro Moradasferreira, Martin E Barriosllerena, Phillip C WrightAbstract:Gloeothece sp. PCC 6909 is a unicellular N(2)-fixing cyanobacterium with a well defined and highly developed sheath surrounding its cells. A sheathless mutant of this strain was previously obtained by chemical mutagenesis and, although lacking the sheath, it releases large amounts of polysaccharides into the culture medium. To provide a global understanding on the metabolic differences between the two phenotypes, the proteomes of the wild type and mutant were analyzed using a cross-species proteomics approach coupled with iTRAQ isobaric tagging technology, since their genome sequences are not yet available. Effects arising from the presence/absence of nitrate and sulfur are presented as two metabolically directed follow-up iTRAQ studies. These nutrients are believed to play a major role in Gloeothece's metabolism, including the production of extracellular polymeric substances - EPS. 454, 124, and 53 proteins were identified and reliably quantified using homology anchoring approaches for iTRAQ previously described. The results obtained strongly suggest that the chemical mutagenesis affected the regulation of a number of key cellular processes, as revealed by the significant fold changes observed for proteins covering a large spectrum of functional groups. Moreover, they provide new insights on the adaptations of Gloeothece cells to nitrate-deficiency and sulfur-limitation.
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sheathless mutant of cyanobacterium Gloeothece sp strain pcc 6909 with increased capacity to remove copper ions from aqueous solutions
Applied and Environmental Microbiology, 2008Co-Authors: Ernesto Micheletti, Paula Tamagnini, Pedro Moradasferreira, S Pereira, Francesca Mannelli, Roberto De PhilippisAbstract:Cyanobacteria are a large and widespread group of photoautotrophic microorganisms that combine the ability to perform an oxygenic plant-like photosynthesis with typical prokaryotic features (40). Outside their atypical gram-negative cell walls (15), many strains possess outermost structures, mainly of a polysaccharidic nature, that differ in thickness and consistency. These structures can be referred to as sheaths, capsules, and slimes (4). The term sheath is applied to the usually thin and electron-dense layer surrounding the cells or the cell groups; the capsule refers to the thick and gelatinous layer intimately associated with the cell surface and presenting sharp outlines, whereas the term slime is used to designate the mucilaginous material that is dispersed around the organism but does not reflect the shape of the cells. During cell growth, aliquots of these polysaccharides can be released into the surrounding medium (referred to as released exocellular polysaccharides [RPS]), causing a progressive increase in its viscosity (4). The cyanobacterial exopolysaccharides (EPSs; a general term which includes both the polysaccharidic structures that remain intimately associated with the cell, i.e., the sheath and capsule, and those released into the culture medium, i.e., the RPS) exhibit some typical characteristics that distinguish them from the polymers synthesized by other bacteria: they frequently contain two different uronic acids, they build a polymer particularly rich in negatively charged groups, they possess a larger number of different monosaccharides, which increases the number of possible conformations of the polymer, and they contain sulfate groups, a unique feature among prokaryotes and one that is shared by the EPSs produced by Archaea (5, 31). At present, heavy metals are one of the most widespread causes of pollution, and their continuous accumulation in water bodies and soils constitutes a serious hazard to both the environment and human health (11, 20). The use of EPS-producing microorganisms (or isolated EPSs) is a valid alternative to conventional chemical and physicochemical methods to remove metallic cations from polluted waters (35). This new technology presents advantages such as the use of natural and renewable sources, reduced costs, rapid kinetics of metal removal, the ability to remove metallic ions present at low concentrations, the possibility to treat contaminated waters simultaneously with several different metal ions, and the possibility of recovering valuable metals from the biosorbent (6, 18). In this context, EPS-producing cyanobacteria appear to be promising candidates due to the unique characteristics of their polysaccharidic envelopes (see above). The efficiency of cyanobacterial EPS in the removal of metal ions has been discussed previously, with an emphasis on the monosaccharidic composition of the polymer, the isolation of EPS, and the subsequent utilization with removal assays (5, 8, 21). Although the chemical composition of the sheaths of several cyanobacterial strains has been determined (14, 15, 32, 33, 38, 39) and the importance of the capsules and RPS in the metal-removal process has been recognized (6), information about the exact contribution of each type of EPSs and/or functional group to the biosorption of the metal is still very limited. This work aimed to understand the role of the various outermost polysaccharidic investments in the process of copper removal by the unicellular N2-fixing cyanobacterium Gloeothece sp. strain PCC 6909. This strain is characterized by a well-defined laminated sheath that encloses cells and cell groups, maintaining a firm colonial structure. In this study, both the wild-type and a sheathless mutant, previously obtained by chemical mutagenesis, were used to elucidate the contribution of each type of EPS to the metal-removal process. Moreover, chemical and physical analyses were performed to identify the major sites responsible for the metal binding.
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sheathless mutant of cyanobacterium Gloeothece sp strain pcc 6909 with increased capacity to remove copper ions from
2008Co-Authors: Ernesto Micheletti, Paula Tamagnini, Pedro Moradasferreira, S Pereira, Francesca Mannelli, Roberto De PhilippisAbstract:The cyanobacterium Gloeothece sp. strain PCC 6909 and its sheathless mutant were tested for their abilities to remove copper ions from aqueous solutions, with the aim of defining the role of the various outermost polysaccharidic investments in the removal of the metal ions. Microscopy studies and chemical analyses revealed that, although the mutant does not possess a sheath, it releases large amounts of polysaccharidic material (released exocellular polysaccharides [RPS]) into the culture medium. The RPS of the wild type and the mutant are composed of the same 11 sugars, although they are present in different amounts, and the RPS of the mutant possesses a larger amount of acidic sugars and a smaller amount of deoxysugars than the wild type. Unexpectedly, whole cultures of the mutant were more effective in the removal of the heavy metal than the wild type (46.3 3.1 and 26.7 1.5 mg of Cu 2 removed per g of dry weight, respectively). Moreover, we demonstrated that the contribution of the sheath to the metal-removal capacity of the wild type is scarce and that the RPS of the mutant is more efficient in removing copper. This suggests that the metal ions are preferably bound to the cell wall and to RPS functional groups rather than to the sheath. Therefore, the increased copper binding efficiency observed with the sheathless mutant can be attributed to the release of a polysaccharide containing larger amounts and/or more accessible functional groups (e.g., carboxyl and amide groups).
Nicholas Willoughby - One of the best experts on this subject based on the ideXlab platform.
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luminescent photobioreactor design for improved algal growth and photosynthetic pigment production through spectral conversion of light
Bioresource Technology, 2013Co-Authors: Seyedeh Fatemeh Mohsenpour, Nicholas WilloughbyAbstract:Growth characteristics of two strains of microalgae in bubble column photobioreactors were investigated under different cultivation conditions. Chlorella vulgaris and Gloeothece membranacea were cultivated in luminescent acrylic photobioreactors at different seed culture densities. Luminescent acrylic photobioreactors in blue, green, yellow, orange, and red colours capable of spectral conversion of light were used. The results indicated that the red luminescent photobioreactor enhanced biomass production in both strains of microalgae while pigmentation was induced under different light colours. Green light promoted chlorophyll production in C. vulgaris however chlorophyll production in G. membranacea cultures was less influenced by the light condition or culture density. Phycobiliproteins were the dominant pigments in G. membranacea and red light favoured synthesis of these pigments.
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spectral conversion of light for enhanced microalgae growth rates and photosynthetic pigment production
Bioresource Technology, 2012Co-Authors: Seyedeh Fatemeh Mohsenpour, Bryce S Richards, Nicholas WilloughbyAbstract:The effect of light conditions on the growth of green algae Chlorella vulgaris and cyanobacteria Gloeothece membranacea was investigated by filtering different wavelengths of visible light and comparing against a model daylight source as a control. Luminescent acrylic sheets containing violet, green, orange or red dyes illuminated by a solar simulator produced the desired wavelengths of light for this study. From the experimental results the highest specific growth rate for C. vulgaris was achieved using the orange range whereas violet light promoted the growth of G. membranacea. Red light exhibited the least efficiency in conversion of light energy into biomass in both strains of microalgae. Photosynthetic pigment formation was examined and maximum chlorophyll-a production in C. vulgaris was obtained by red light illumination. Green light yielded the best chlorophyll-a production in G. membranacea. The proposed illumination strategy offers improved microalgae growth without resorting to artificial light sources, reducing energy use and costs of cultivation.