The Experts below are selected from a list of 1821 Experts worldwide ranked by ideXlab platform
Brigitte Gontero - One of the best experts on this subject based on the ideXlab platform.
-
Glyceraldehyde-3-phosphate dehydrogenase is regulated by ferredoxin-NADP reductase in the diatom Asterionella Formosa
New Phytologist, 2014Co-Authors: Malika Mekhalfi, Carine Puppo, Luisana Avilan, Régine Lebrun, Pascal Mansuelle, Stephen C. Maberly, Brigitte GonteroAbstract:Diatoms are a widespread and ecologically important group of heterokont algae that contribute c. 20% to global productivity. Previous work has shown that regulation of their key Calvin cycle enzymes differs from that of the Plantae, and that in crude extracts, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) can be inhibited by nicotinamide adenine dinucleotide phosphate reduced (NADPH) under oxidizing conditions. The freshwater diatom, Asterionella Formosa, was studied using enzyme kinetics, chromatography, surface plasmon resonance, mass spectrometry and sequence analysis to determine the mechanism behind this GAPDH inhibition. GAPDH interacted with ferredoxin–nicotinamide adenine dinucleotide phosphate (NADP) reductase (FNR) from the primary phase of photosynthesis, and the small chloroplast protein, CP12. Sequences of copurified GAPDH and FNR were highly homologous with published sequences. However, the widespread ternary complex among GAPDH, phosphoribulokinase and CP12 was absent. Activity measurements under oxidizing conditions showed that NADPH can inhibit GAPDH-CP12 in the presence of FNR, explaining the earlier observed inhibition within crude extracts. Diatom plastids have a distinctive metabolism, including the lack of the oxidative pentose phosphate pathway, and so cannot produce NADPH in the dark. The observed down-regulation of GAPDH in the dark may allow NADPH to be rerouted towards other reductive processes contributing to their ecological success.
-
Effect of environmental conditions on various enzyme activities and triacylglycerol contents in cultures of the freshwater diatom, Asterionella Formosa (Bacillariophyceae)
Biochimie, 2014Co-Authors: Malika Mekhalfi, Sawsan Amara, Sylvie Robert, Frédéric Carrière, Brigitte GonteroAbstract:A detailed analysis of triacylglycerols (TAGs) contents, fatty acid patterns and key enzyme activities in the freshwater diatom Asterionella Formosa was performed under various conditions, including nitrate, iron and silicon limitation (stress conditions), or bicarbonate and phytohormones supplementation (stimulation conditions). Of all the conditions tested, the addition of bicarbonate produced the greatest increase (5-fold) in TAGs contents compared to the control while the biomass increased. The addition of phytohormones also allowed a significant increase in TAGs of about 3-fold while the biomass increased. Silicon, unlike iron and nitrate limitation, also triggered a significant increase in TAGs contents of 3.5-fold but negatively affected the biomass. Analysis of fatty acid profiles showed that the mono-unsaturated C16:1 fatty acid was the most abundant in A. Formosa, followed by C16:0, C14:0 and eicosapentaenoic acid (EPA; C20:5 n-3). EPA levels were found to increase under nitrate and iron limitation. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH), phosphoribulokinase (PRK), phosphofructokinase (PFK), glucose-6-phosphate dehydrogenase (G6PDH) and malate dehydrogenase (MDH) activities differed with growth conditions. Most enzymes were up-regulated in stimulated cells while in the case of stressed cells, the pattern of activities was more variable. Detailed analysis of all enzyme activities showed that the most important enzyme among those tested was GAPDH which could be a good candidate for genetic engineering of high lipid-producing algae. This study provides a better understanding of key enzymes and biochemical pathways involved in lipid accumulation processes in diatoms.
-
Consequences of the presence of 24-epibrassinolide, on cultures of a diatom, Asterionella Formosa.
Biochimie, 2012Co-Authors: Malika Mekhalfi, Luisana Avilan, Régine Lebrun, Hugo Botebol, Brigitte GonteroAbstract:Addition of the plant hormone 24-epibrassinolide to culture media stimulated the growth of a freshwater diatom, Asterionella Formosa. The hormone stimulated activity of glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a key enzyme from Calvin cycle, by 6-fold. Other key metabolic enzymes, phosphofructokinase and malate dehydrogenase were also stimulated but to a lesser extent. The activity of glucose-6-phosphate dehydrogenase, involved in the oxidative pentose phosphate pathway, also increased in the presence of the hormone but only under non reducing conditions. In cells stimulated by epibrassinolide, activated enzymes were sensitive to oxidized-DTT. GAPDH purified from cells grown in the presence of the hormone was not associated with a small protein of 8.5 kDa shown to be similar to CP12. Consequently the activity of GAPDH was no longer regulated by either oxidizing or reducing conditions. Among enzymes that, like GAPDH, responded positively to reducing agent were fructose-1,6-bisphosphatase (FBPase) and glucose-6-phosphate dehydrogenase (G6PDH). These enzymes were also sensitive to, and were negatively regulated by, oxidized-DTT. The activities in extracts from illuminated cells differed from those from darkened cells: FBPase, G6PDH and GAPDH, that were activated by DTT in darkened cells were no more activated in illuminated cells, but were oxidized by oxidized-DTT. Thus, oxidizing or reducing conditions mimic the conditions in dark and light, respectively. Unlike the other enzymes, phosphofructokinase (PFK) was inhibited by DTT but oxidized-DTT reversed this effect. The enzymes shown to be redox regulated in vitro by reduction/oxidation are very likely candidates for regulation in vivo by thioredoxins.
-
SPECIFICITY AND FUNCTION OF GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE IN A FRESHWATER DIATOM, Asterionella Formosa (BACILLARIOPHYCEAE)(1).
Journal of phycology, 2008Co-Authors: Jenny Erales, Brigitte Gontero, Stephen C. MaberlyAbstract:The plastidic GAPDH catalyses the only reductive step in the Calvin cycle and exists as different forms of which GapC1 enzyme is present in chromalveolates such as diatoms. Biochemical studies on diatoms are still fragmentary and thus, in this report, GAPDH from the freshwater diatom Asterionella Formosa Hassall, has been purified and kinetically characterised. It is a homotetrameric enzyme with a molecular mass of about 150 ± 15 kDa. The enzyme showed Michaelis-Menten kinetics with respect to both cofactors, NADPH and NADH, with a 16-fold greater catalytic constant for NADPH. The Km for NADPH was 140 µM, the lowest affinity reported, while the catalytic constant, 815 s-1, is the highest reported. The Km for NADH was 93 µM and the catalytic constant was 50 s-1, both are similar to reported values for other types of GAPDH. The GapC1 enzyme, like the Chlamydomonas reinhardtii P.A. Dang A4 GAPDH, exhibits a cooperative behaviour towards the substrate, BPGA, with both cofactors. Mass spectrometry analysis showed that when GapC1 enzyme was purified without reducing agents, it co-purified with a small protein with a mass of 8.2 kDa. This protein was recognized by antibodies against CP12. When associated with this protein, GAPDH displayed a lag that disappeared upon incubation with reducing agent in the presence of either BPGA or NADPH as a consequence of dissociation of the GAPDH/CP12 complex. Thus, as in other species of algae and higher plants, regulation of GapC1 enzyme in A. Formosa may occur through association-dissociation processes linked to dark-light transitions.
-
Specificity and function of glyceraldehyde-3-phosphate dehydrogenase in a freshwater diatom, Asterionella Formosa (bacillariophyceae) 1
European Journal of Phycology, 2008Co-Authors: Jenny Erales, Brigitte Gontero, Stephen C. MaberlyAbstract:The plastidic glyceraldehyde-3-phosphate dehydrogenase (GAPDH) catalyzes the only reductive step in the Calvin cycle and exists as different forms of which GapC1 enzyme is present in chromalveolates, such as diatoms. Biochemical studies on diatoms are still fragmentary, and, thus, in this report, GAPDH from the freshwater diatom Asterionella Formosa Hassall has been purified and kinetically characterized. It is a homotetrameric enzyme with a molecular mass of ~150 ± 15 kDa. The enzyme showed Michaelis–Menten kinetics with respect to both cofactors, NADPH and NADH, with a 16-fold greater catalytic constant for NADPH. The Km for NADPH was 140 μM, the lowest affinity reported, while the catalytic constant, 815 s−1, is the highest reported. The Km for NADH was 93 μM, and the catalytic constant was 50 s−1, both are similar to reported values for other types of GAPDH. The GapC1 enzyme, like the Chlamydomonas reinhardtii A4 GAPDH, exhibits a cooperative behavior toward the substrate, 1,3-bisphosphoglyceric acid (BPGA), with both cofactors. Mass spectrometry analysis showed that when GapC1 enzyme was purified without reducing agents, it copurified with a small protein with a mass of 8.2 kDa. This protein was recognized by antibodies against CP12. When associated with this protein, GAPDH displayed a lag that disappeared upon incubation with reducing agent in the presence of either BPGA or NADPH as a consequence of dissociation of the GAPDH/CP12 complex. Thus, as in other species of algae and higher plants, regulation of GapC1 enzyme in A. Formosa may occur through association-dissociation processes linked to dark-light transitions.
John P. Smol - One of the best experts on this subject based on the ideXlab platform.
-
Why is the relative abundance of Asterionella Formosa increasing in a Boreal Shield lake as nutrient levels decline
Journal of Paleolimnology, 2016Co-Authors: Branaavan Sivarajah, Kathleen M. Rühland, Andrew L. Labaj, Andrew M. Paterson, John P. SmolAbstract:The freshwater diatom Asterionella Formosa Hassall is a widely distributed species whose populations have been increasing in the recent sediments of numerous lakes worldwide. This taxon’s proliferation has commonly been associated with nutrient enrichment and, more recently, with twentieth century increases in atmospheric nitrogen deposition. However, a growing number of studies have reported increases in A. Formosa in the absence of increased nutrients and have thus raised questions about whether alternative causative factors (such as recent climate warming) may be important. Here we assess the relative importance of nutrients and climate warming on A. Formosa by comparing regional air temperature trends and 20 years of annually measured lake water nutrients (total inorganic nitrogen, total nitrogen, and total phosphorus) with past changes in relative abundance of this taxon from a sediment core obtained from a soft-water, Boreal Shield lake (George Lake, Killarney, Ontario). Measured lake water total phosphorus has always been very low and remains so to the present (
-
why is the relative abundance of Asterionella Formosa increasing in a boreal shield lake as nutrient levels decline
Journal of Paleolimnology, 2016Co-Authors: Branaavan Sivarajah, Kathleen M. Rühland, Andrew L. Labaj, Andrew M. Paterson, John P. SmolAbstract:The freshwater diatom Asterionella Formosa Hassall is a widely distributed species whose populations have been increasing in the recent sediments of numerous lakes worldwide. This taxon’s proliferation has commonly been associated with nutrient enrichment and, more recently, with twentieth century increases in atmospheric nitrogen deposition. However, a growing number of studies have reported increases in A. Formosa in the absence of increased nutrients and have thus raised questions about whether alternative causative factors (such as recent climate warming) may be important. Here we assess the relative importance of nutrients and climate warming on A. Formosa by comparing regional air temperature trends and 20 years of annually measured lake water nutrients (total inorganic nitrogen, total nitrogen, and total phosphorus) with past changes in relative abundance of this taxon from a sediment core obtained from a soft-water, Boreal Shield lake (George Lake, Killarney, Ontario). Measured lake water total phosphorus has always been very low and remains so to the present (<10 µg L−1). Total inorganic nitrogen (TIN) and total nitrogen (TN) concentrations, however, show distinct declining trends (p < 0.05) at George Lake since the 1990s, when substantial increases in mean annual and mean winter air temperatures (p < 0.01) were also recorded. These declines in lake water nitrogen concentrations match declines in atmospherically deposited nitrogen in this region. Since the late-1980s and early-1990s, there has been a marked increase in the relative abundance of A. Formosa, which had been virtually absent from the lake’s sediment record in earlier intervals. A. Formosa trends closely track increasing regional air temperatures, but also clearly coincide with declines in lake water nutrients and decreases in regional nitrogen deposition (p < 0.01). These trends have also occurred in other lakes in the region. Our results show that increases in nitrogen deposition and/or nutrient enrichment are not pre-conditions for increases in the relative abundance of A. Formosa. Instead, warming-related changes including longer open water periods, changes in lake mixing regimes, and lake thermal properties might have contributed to the recent increase in the relative abundance of A. Formosa in this lake and likely elsewhere.
Arif Gönülol - One of the best experts on this subject based on the ideXlab platform.
-
A Study on the Phytoplankton of Hasan UĞURLU Dam Lake (Samsun-Turkey)
Turkish Journal of Biology, 1998Co-Authors: Arif GönülolAbstract:The composition and seasonal variations of phytoplankton of Hasan UGURLU Dam Lake were studied using samples collected from two stations between July 1992 to December 1993. 57 taxa were identified belonging to the Bacillariophyta, Chlorophyta, Cyanophyta, Dinophyta and Euglenophyta divisions of phytoplankton. In the phytoplankton, Asterionella Formosa, Cyclotella planc-tonica, Pediastrum simplex and Ceratium hirundinella caused water blooms in certain months. The light density and temperature affected the composition and seasonal variations in phytoplankton considerably. Nutrient levels in the lake did not limit the seasonal variations in phytoplankton. It was determined that Lake Hasan Ugurlu had mesotrophic characteristics because of the morpho-metric structure, physical and chemical properties of the water and a phytoplankton type which caused water blooming by various taxa during certain months
-
Seasonal Variations of Phytoplankton Blooms in Suat Ugurlu (Samsun - Turkey)
Turkish Journal of Botany, 1998Co-Authors: Arif GönülolAbstract:The seasonal variations in phytoplankton blooms in Suat Ugurlu Reservoir were studied between July 1992 and De-cember 1993. In certain months, the species Asterionella Formosa Hassal, Cyclotella planctonica Brunthaler, Melosira granulata (Ehr.) Ralfs (Bacillariophyta); Pediastrum simplex Meyen, Pandorina morum Borry (Chlorophyta) and Ceratium hirundinella (O F. Muller) Schrank (Dinophyta) produced blooms in the lake. During the study period, the measured N/P ratio in the water varied from 10.3 mg/lt to 62.5. In accordance with these variations, P. simplex, P. morum and C. hirundinella, which consume high levels of phosphate, produced blooms in summer, whereas the blooms in winter were produced by A. Formosa, C. planctonica and M. granulata, which consume more nitrate than phosphate.
Jean-michel Claverie - One of the best experts on this subject based on the ideXlab platform.
-
Exploring the microbiome of the "star" freshwater diatom Asterionella Formosa in a laboratory context.
Environmental microbiology, 2018Co-Authors: Mila Kojadinovic-sirinelli, Adrien Villain, Carine Puppo, Laura Prioretti, Pierre Hubert, Yizhi Zhang, Gianluca Gregori, Sophie Fon Sing, Jean-françois Sassi, Jean-michel ClaverieAbstract:Most of our knowledge on the mechanisms underlying diatom-bacterial interactions has been acquired through studies involving isolation of culturable partners. Here, we established a laboratory model of intermediate complexity between complex natural communities and laboratory pure culture models. We investigated the whole community formed by the freshwater diatom Asterionella Formosa and its associated bacteria in a laboratory context, including both culturable and unculturable bacteria. Combining cellular and molecular approaches, we showed that in laboratory cultures, A. Formosa microbiome was dynamic and comprised of numerous bacterial species (mainly Proteobacteria and Bacteroidetes). Using metagenomics, we explored several metabolic potentials present within the bacterial community. Our analyses suggested that bacteria were heterotrophic although a third of them (Alpha- and Beta-proteobacteria) could also be phototrophic. About 60% of the bacteria, phylogenetically diverse, could metabolize glycolate. The capacity to synthesize molecules such as B vitamins appeared unevenly distributed among bacteria. Altogether, our results brought insights into the bacterial diversity found in diatom-bacterial communities and hinted at metabolic interdependencies within the community that could result in diatom-bacterial and bacterial-bacterial interactions. The present work allowed us to explore the functional architecture of the bacterial community associated with A. Formosa in culture and is complementary to field studies. This article is protected by copyright. All rights reserved.
-
Exploring the microbiome of the “star” freshwater diatom Asterionella Formosa in a laboratory context
'Wiley', 2018Co-Authors: Mila Kojadinovic-sirinelli, Adrien Villain, Carine Puppo, Laura Prioretti, Pierre Hubert, Yizhi Zhang, Grégori Gérald, Sophie Fon Sing, Jean-françois Sassi, Jean-michel ClaverieAbstract:International audienceMost of our knowledge on the mechanisms underlying diatom-bacterial interactions has been acquired through studies involving isolation of culturable partners. Here, we established a laboratory model of intermediate complexity between complex natural communities and laboratory pure culture models. We investigated the whole community formed by the freshwater diatom Asterionella Formosa and its associated bacteria in a laboratory context, including both culturable and unculturable bacteria. Combining cellular and molecular approaches, we showed that in laboratory cultures, A. Formosa microbiome was dynamic and comprised of numerous bacterial species (mainly Proteobacteria and Bacteroidetes). Using metagenomics, we explored several metabolic potentials present within the bacterial community. Our analyses suggested that bacteria were heterotrophic although a third of them (Alpha- and Beta-proteobacteria) could also be phototrophic. About 60% of the bacteria, phylogenetically diverse, could metabolize glycolate. The capacity to synthesize molecules such as B vitamins appeared unevenly distributed among bacteria. Altogether, our results brought insights into the bacterial diversity found in diatom-bacterial communities and hinted at metabolic interdependencies within the community that could result in diatom-bacterial and bacterial-bacterial interactions. The present work allowed us to explore the functional architecture of the bacterial community associated with A. Formosa in culture and is complementary to field studies. This article is protected by copyright. All rights reserved
-
Complete mitochondrial genome sequence of the freshwater diatom Asterionella Formosa
Mitochondrial DNA Part B, 2017Co-Authors: Adrien Villain, Mila Kojadinovic, Carine Puppo, Laura Prioretti, Pierre Hubert, Yizhi Zhang, Gianluca Gregori, Alain Roulet, Céline Roques, Jean-michel ClaverieAbstract:We report the complete mitochondrial genome sequence of the freshwater diatom Asterionella Formosa. The large 61.9 kb circular sequence encodes 34 proteins and 25 tRNAs that are universally conserved in other sequenced diatoms. We fully resolved a unique 24 kb region containing highly conserved repeated sequence units, possibly collocating with an origin of replication.
Masayuki Takahashi - One of the best experts on this subject based on the ideXlab platform.
-
Physico-chemical control of the growth of a diatom, Asterionella Formosa Hass., in a shallow eutrophic lake
2016Co-Authors: Sakae Kudoh, Masayuki TakahashiAbstract:Abstract. Physico-chemical environmental control of the growth rate of an algal population, the pennate diatom Asterionella Formosa Hass., was investigated for a year in natural water. This species occurred in vegetative form in the water column all the time, although its population density varied by five orders of magnitude from a maximum of 1.4 x 10 * cells 1 in February to a minimum of 0.8 x 101 cells r 1 in August. A mathematical model of a combination of multiplicative and Liebig types suggested that vegetative cells were severely limited in their growth rate, reaching almost 80% depression of the maximum rate between December and February by low temperatures and nearly 50 % depression in warm seasons by light intensity. Nutrient limitations were only observed in May, August and September, although they were not as great as by temperature and light intensity in the study lake. Population changing rates oiA.Formosa determined in the lake were low and agreed well with the estimated growth rates during winter, but those in summer were low and disagreed with the estimated high growth rates. This suggests that population change of the species was highly dependent upon the specific growth rate in winter, but other factors became predominant i
-
temperature dependent changes in colony size of the freshwater pennate diatom Asterionella Formosa bacillariophyceae and their possible ecological implications1
Journal of Phycology, 1994Co-Authors: Toshiyuki Hayakawa, Sakae Kudoh, Y. Suzuki, Masayuki TakahashiAbstract:Changes in colony size (cell number per colony) of Asterionella Formosa Hass. were experimentally evaluated in relation to water temperature using two types of clones having colony sizes of four or eight cells. The clones were isolated from two different temperate freshwater lakes. Both clones showed the same general trend with changing temperature. Most of the colonies were normal in size at low temperatures, but colony size was twice as large at high temperatures. Variable colony sizes were present at low percentages. Colony separation occurred at the oldest connection within the colony after cell division. Culture experiments showed that the rates of specific growth and colony separation were balanced except for a rather short period of time when the temperature was changed. Optical and scanning electron micrography did not show any distinctive morphological structure at the point of connection except for porelli and mucilage pads. Seasonal changes in colony size of A. Formosa observed in a freshwater lake are discussed based on these temperature results.
-
TEMPERATURE‐DEPENDENT CHANGES IN COLONY SIZE OF THE FRESHWATER PENNATE DIATOM Asterionella Formosa (BACILLARIOPHYCEAE) AND THEIR POSSIBLE ECOLOGICAL IMPLICATIONS1
Journal of Phycology, 1994Co-Authors: Toshiyuki Hayakawa, Sakae Kudoh, Y. Suzuki, Masayuki TakahashiAbstract:Changes in colony size (cell number per colony) of Asterionella Formosa Hass. were experimentally evaluated in relation to water temperature using two types of clones having colony sizes of four or eight cells. The clones were isolated from two different temperate freshwater lakes. Both clones showed the same general trend with changing temperature. Most of the colonies were normal in size at low temperatures, but colony size was twice as large at high temperatures. Variable colony sizes were present at low percentages. Colony separation occurred at the oldest connection within the colony after cell division. Culture experiments showed that the rates of specific growth and colony separation were balanced except for a rather short period of time when the temperature was changed. Optical and scanning electron micrography did not show any distinctive morphological structure at the point of connection except for porelli and mucilage pads. Seasonal changes in colony size of A. Formosa observed in a freshwater lake are discussed based on these temperature results.
