The Experts below are selected from a list of 2106 Experts worldwide ranked by ideXlab platform
Claudia Wiedner - One of the best experts on this subject based on the ideXlab platform.
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Cyanobacteria and Cyanotoxins: The Influence of Nitrogen versus Phosphorus
PloS one, 2012Co-Authors: Andrew M. Dolman, Jacqueline Rucker, Jutta Fastner, Frances R. Pick, Thomas Rohrlack, Ute Mischke, Claudia WiednerAbstract:The importance of nitrogen (N) versus phosphorus (P) in explaining total cyanobacterial biovolume, the biovolume of specific cyanobacterial taxa, and the incidence of cyanotoxins was determined for 102 north German lakes, using methods to separate the effects of joint variation in N and P concentration from those of differential variation in N versus P. While the positive relationship between total cyanobacteria biovolume and P concentration disappeared at high P concentrations, cyanobacteria biovolume increased continually with N concentration, indicating potential N limitation in highly P enriched lakes. The biovolumes of all cyanobacterial taxa were higher in lakes with above average joint NP concentrations, although the relative biovolumes of some Nostocales were higher in less enriched lakes. Taxa were found to have diverse responses to differential N versus P concentration, and the differences between taxa were not consistent with the hypothesis that potentially N2-fixing Nostocales taxa would be favoured in low N relative to P conditions. In particular Aphanizomenon gracile and the subtropical invasive species Cylindrospermopsis raciborskii often reached their highest biovolumes in lakes with high nitrogen relative to phosphorus concentration. Concentrations of all cyanotoxin groups increased with increasing TP and TN, congruent with the biovolumes of their likely producers. Microcystin concentration was strongly correlated with the biovolume of Planktothrix agardhii but concentrations of anatoxin, cylindrospermopsin and paralytic shellfish poison were not strongly related to any individual taxa. Cyanobacteria should not be treated as a single group when considering the potential effects of changes in nutrient loading on phytoplankton community structure and neither should the N2-fixing Nostocales. This is of particular importance when considering the occurrence of cyanotoxins, as the two most abundant potentially toxin producing Nostocales in our study were found in lakes with high N relative to P enrichment.
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A CARD-FISH protocol for the identification and enumeration of cyanobacterial akinetes in lake sediments.
FEMS microbiology ecology, 2012Co-Authors: Jessica Ramm, Jacqueline Rucker, Claudia Wiedner, Andreas Ballot, Ora Hadas, Achsa Lupu, Assaf SukenikAbstract:Akinetes are the dormant cells of Nostocales (cyanobacteria) that enable the organisms to survive harsh environmental conditions while resting in bottom sediments. The germination of akinetes assists the dispersal and persistence of the species. The assessment of the akinete pool in lake sediments is essential to predict the bloom formation of the Nostocales population. We present here the implementation of an improved catalysed reporter deposition (CARD)–fluorescence in situ hybridization (FISH) protocol to assist the identification and quantification of akinetes in sediment samples. Several 16S rRNA gene oligonucleotide probes were evaluated for labelling akinetes of various species of Anabaena, Aphanizomenon and Cylindrospermopsis. Akinetes of all the taxa studied were successfully labelled and could be easily detected by their bright fluorescence signal. The probes' specificity was tested with 32 strains of different taxa. All six Cylindrospermopsis raciborskii strains were labelled with a specific probe for its 16S rRNA gene. A more general probe labelled 73% of the Anabaena and Aphanizomenon strains. The counting data of field samples obtained with CARD-FISH and the regular light microscopy approach did not differ significantly, confirming the suitability of both methods. The CARD-FISH approach was found to be less time-consuming because of better visibility of akinetes.
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Modelling life cycle and population dynamics of Nostocales (cyanobacteria)
Environmental Modelling & Software, 2011Co-Authors: Klaus Jöhnk, Jacqueline Rucker, Brigitte Nixdorf, Rainer Brüggemann, B. Luther, U. Simon, Claudia WiednerAbstract:Cyanobacteria of the order Nostocales found in lakes in temperate regions are generally assumed to benefit from climate change. To predict their future development under varying environmental conditions, we developed a mathematical model that simulates their entire life cycle. Cylindrospermopsis raciborskii, a tropical species which spread to the northern temperate zone during the last decades, was used as the model organism. We calibrated and validated the model using a 13-year data set on the species' population dynamics gathered in a shallow lake in northern Germany. The predicted values were consistent with the observed data. We used sensitivity studies and Hasse diagrams based on partial order theory to rank the impact of different model parameters on life cycle dynamics. Our results show that the seasonal dynamics of C. raciborskii are mainly determined by the optimum growth temperature of its vegetative cells. The dynamics of pelagic populations in the water and akinete populations (resting stages) in the sediment is highly dependent on lake water temperature and underwater light intensity and, thus, on climatic conditions. Therefore, any future increase in lake water temperature will presumably lead to an increase in the size of C. raciborskii populations in particular and of Nostocales populations in general.
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Competitiveness of invasive and native cyanobacteria from temperate freshwaters under various light and temperature conditions
Journal of Plankton Research, 2010Co-Authors: Grit Mehnert, Jacqueline Rucker, Brigitte Nixdorf, Samuel Cirés, Franziska Leunert, Klaus Jöhnk, Claudia WiednerAbstract:Some tropical cyanobacteria spread to temperate freshwaters during the last decades. To evaluate their further development in temperate lakes we studied the temperature- and light-dependent growth of three invasive (Cylindrospermopsis raciborskii, Anabaena bergii, Aphanizomenon aphanizomenoides) and three native (Aphanizomenon gracile, Aphanizomenon flos-aquae, Anabaena macrospora) cyanobacterial species (Nostocales) from German lakes. We also included one potentially invasive (Aphanizomenon ovalisporum) Nostocales species. We conducted semi-continuous culture experiments and a microcosm experiment along a natural light gradient. Temperature data were used to design a model to simulate the development of selected species according to three temperature scenarios (past, present and future). Native species had significantly higher growth rates than invasive species and the potential invader A. ovalisporum at low temperatures (≤ 10°C), while the opposite was true at high temperatures (≥ 35°C). Maximum growth rates of A. ovalisporum, A. aphanizomenoides and C. raciborskii were clearly higher than those of A. bergii and the native species. Regarding light-dependent growth, significant differences were found between single species but not between all native and invasive species. The model simulation demonstrates a shift in dominance from the native A. gracile in the historic scenario to C. raciborskii populations in the future scenario, in which also the potential invader A. ovalisporum is able to establish populations in temperate lakes. Our findings suggest that any further temperature increase would promote the growth and development of Nostocales species in general, and that of the invasive species in particular, and would enable a more northward expansion of A. ovalisporum.
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Competitiveness of invasive and native cyanobacteria from temperate freshwaters under various light and temperature conditions
Journal of Plankton Research, 2010Co-Authors: Grit Mehnert, Jacqueline Rucker, Brigitte Nixdorf, Samuel Cirés, Franziska Leunert, Klaus Jöhnk, Claudia WiednerAbstract:Some tropical cyanobacteria have spread to temperate freshwaters during the last decades. To evaluate their further development in temperate lakes, we studied the temperature- and light-dependent growth of three invasive (Cylindrospermopsis raciborskii, Anabaena bergii and Aphanizomenon aphanizomenoides) and three native (Aphanizomenon gracile, Aphanizomenon flos-aquae and Anabaena macrospora) cyanobacterial species (Nostocales) from German lakes. We also included one potentially invasive (Aphanizomenon ovalisporum) Nostocales species. We conducted semi-continuous culture experiments and a microcosm experiment along a natural light gradient. Temperature data were used to design a model to simulate the development of selected species according to three temperature scenarios (past, present and future). Native species had significantly higher growth rates than invasive species and the potential invader A. ovalisporum at low temperatures (� 108C), while the opposite was true at high temperatures (� 358C). Maximum growth rates of A. ovalisporum, A. aphanizomenoides and C. raciborskii were clearly higher than those of A. bergii and the native species. Regarding light-dependent growth, significant differences were found between single species but not between all native and invasive species. The model simulation demonstrates a shift in dominance from the native A. gracile in the historic scenario to C. raciborskii populations in the future scenario, in which also the potential invader A. ovalisporum is able to establish populations in temperate lakes. Our findings suggest that any further temperature increase would promote the growth and development of Nostocales species in general, and that of the invasive species in particular, and would enable a more northward expansion of A. ovalisporum.
Jacqueline Rucker - One of the best experts on this subject based on the ideXlab platform.
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Dormant Cells (Akinetes) of Filamentous Cyanobacteria Demonstrate a Great Variability in Morphology, Physiology, and Ecological Function
Cyanobacteria, 2019Co-Authors: Assaf Sukenik, Jacqueline Rucker, Iris MaldenerAbstract:Abstract Akinetes are dormant cells of cyanobacteria species from the Nostocales and Stigonematales orders, allowing these phototrophic bacteria to survive in harsh and starvation conditions. These spore-like thick-walled, nonmotile cells differentiate from vegetative cells in response to environmental fluctuations. They serve a perennating role as they maintain the ability to resume the morphology and functions of vegetative cells including the renewal of cell division after a long period of dormancy. Here, we review recent advances in studies of akinetes emphasizing environmental triggers, cellular responses, morphological, and structural changes that occur during akinete differentiation and germination. Variations in akinete formation, structure, and metabolism among different species are highlighted and their role in bloom formation of Nostocales species is demonstrated.
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Cyanobacteria and Cyanotoxins: The Influence of Nitrogen versus Phosphorus
PloS one, 2012Co-Authors: Andrew M. Dolman, Jacqueline Rucker, Jutta Fastner, Frances R. Pick, Thomas Rohrlack, Ute Mischke, Claudia WiednerAbstract:The importance of nitrogen (N) versus phosphorus (P) in explaining total cyanobacterial biovolume, the biovolume of specific cyanobacterial taxa, and the incidence of cyanotoxins was determined for 102 north German lakes, using methods to separate the effects of joint variation in N and P concentration from those of differential variation in N versus P. While the positive relationship between total cyanobacteria biovolume and P concentration disappeared at high P concentrations, cyanobacteria biovolume increased continually with N concentration, indicating potential N limitation in highly P enriched lakes. The biovolumes of all cyanobacterial taxa were higher in lakes with above average joint NP concentrations, although the relative biovolumes of some Nostocales were higher in less enriched lakes. Taxa were found to have diverse responses to differential N versus P concentration, and the differences between taxa were not consistent with the hypothesis that potentially N2-fixing Nostocales taxa would be favoured in low N relative to P conditions. In particular Aphanizomenon gracile and the subtropical invasive species Cylindrospermopsis raciborskii often reached their highest biovolumes in lakes with high nitrogen relative to phosphorus concentration. Concentrations of all cyanotoxin groups increased with increasing TP and TN, congruent with the biovolumes of their likely producers. Microcystin concentration was strongly correlated with the biovolume of Planktothrix agardhii but concentrations of anatoxin, cylindrospermopsin and paralytic shellfish poison were not strongly related to any individual taxa. Cyanobacteria should not be treated as a single group when considering the potential effects of changes in nutrient loading on phytoplankton community structure and neither should the N2-fixing Nostocales. This is of particular importance when considering the occurrence of cyanotoxins, as the two most abundant potentially toxin producing Nostocales in our study were found in lakes with high N relative to P enrichment.
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A CARD-FISH protocol for the identification and enumeration of cyanobacterial akinetes in lake sediments.
FEMS microbiology ecology, 2012Co-Authors: Jessica Ramm, Jacqueline Rucker, Claudia Wiedner, Andreas Ballot, Ora Hadas, Achsa Lupu, Assaf SukenikAbstract:Akinetes are the dormant cells of Nostocales (cyanobacteria) that enable the organisms to survive harsh environmental conditions while resting in bottom sediments. The germination of akinetes assists the dispersal and persistence of the species. The assessment of the akinete pool in lake sediments is essential to predict the bloom formation of the Nostocales population. We present here the implementation of an improved catalysed reporter deposition (CARD)–fluorescence in situ hybridization (FISH) protocol to assist the identification and quantification of akinetes in sediment samples. Several 16S rRNA gene oligonucleotide probes were evaluated for labelling akinetes of various species of Anabaena, Aphanizomenon and Cylindrospermopsis. Akinetes of all the taxa studied were successfully labelled and could be easily detected by their bright fluorescence signal. The probes' specificity was tested with 32 strains of different taxa. All six Cylindrospermopsis raciborskii strains were labelled with a specific probe for its 16S rRNA gene. A more general probe labelled 73% of the Anabaena and Aphanizomenon strains. The counting data of field samples obtained with CARD-FISH and the regular light microscopy approach did not differ significantly, confirming the suitability of both methods. The CARD-FISH approach was found to be less time-consuming because of better visibility of akinetes.
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Modelling life cycle and population dynamics of Nostocales (cyanobacteria)
Environmental Modelling & Software, 2011Co-Authors: Klaus Jöhnk, Jacqueline Rucker, Brigitte Nixdorf, Rainer Brüggemann, B. Luther, U. Simon, Claudia WiednerAbstract:Cyanobacteria of the order Nostocales found in lakes in temperate regions are generally assumed to benefit from climate change. To predict their future development under varying environmental conditions, we developed a mathematical model that simulates their entire life cycle. Cylindrospermopsis raciborskii, a tropical species which spread to the northern temperate zone during the last decades, was used as the model organism. We calibrated and validated the model using a 13-year data set on the species' population dynamics gathered in a shallow lake in northern Germany. The predicted values were consistent with the observed data. We used sensitivity studies and Hasse diagrams based on partial order theory to rank the impact of different model parameters on life cycle dynamics. Our results show that the seasonal dynamics of C. raciborskii are mainly determined by the optimum growth temperature of its vegetative cells. The dynamics of pelagic populations in the water and akinete populations (resting stages) in the sediment is highly dependent on lake water temperature and underwater light intensity and, thus, on climatic conditions. Therefore, any future increase in lake water temperature will presumably lead to an increase in the size of C. raciborskii populations in particular and of Nostocales populations in general.
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Akinetes: Dormant Cells of Cyanobacteria
Dormancy and Resistance in Harsh Environments, 2010Co-Authors: Ruth N. Kaplan-levy, Jacqueline Rucker, Ora Hadas, Michael L. Summers, Assaf SukenikAbstract:Cyanobacteria are an ancient and morphologically diverse group of photosynthetic prokaryotes, which were the first to evolve oxygenic photosynthesis. Cyanobacteria are widely distributed in diversed environments. In the case of members of the orders Nostocales and Stigonematales, their persistence and success were attributed to their ability to form specialized cells: heterocysts, capable of fixing atmospheric nitrogen and spore-like cells, the akinetes. This review focuses on akinetes of Nostocales, emphasizing environmental triggers and cellular responses involved in differentiation, maturation, dormancy, and germination of these resting cells. Morphological and structural changes, variation in akinete composition, and metabolism are summarized. Special attention is given to the genetic regulation of the differentiation process in an attempt to close gaps in our understanding of the dormancy phenomenon in cyanobacteria and to identify open questions for future research.
Brigitte Nixdorf - One of the best experts on this subject based on the ideXlab platform.
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Modelling life cycle and population dynamics of Nostocales (cyanobacteria)
Environmental Modelling & Software, 2011Co-Authors: Klaus Jöhnk, Jacqueline Rucker, Brigitte Nixdorf, Rainer Brüggemann, B. Luther, U. Simon, Claudia WiednerAbstract:Cyanobacteria of the order Nostocales found in lakes in temperate regions are generally assumed to benefit from climate change. To predict their future development under varying environmental conditions, we developed a mathematical model that simulates their entire life cycle. Cylindrospermopsis raciborskii, a tropical species which spread to the northern temperate zone during the last decades, was used as the model organism. We calibrated and validated the model using a 13-year data set on the species' population dynamics gathered in a shallow lake in northern Germany. The predicted values were consistent with the observed data. We used sensitivity studies and Hasse diagrams based on partial order theory to rank the impact of different model parameters on life cycle dynamics. Our results show that the seasonal dynamics of C. raciborskii are mainly determined by the optimum growth temperature of its vegetative cells. The dynamics of pelagic populations in the water and akinete populations (resting stages) in the sediment is highly dependent on lake water temperature and underwater light intensity and, thus, on climatic conditions. Therefore, any future increase in lake water temperature will presumably lead to an increase in the size of C. raciborskii populations in particular and of Nostocales populations in general.
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Competitiveness of invasive and native cyanobacteria from temperate freshwaters under various light and temperature conditions
Journal of Plankton Research, 2010Co-Authors: Grit Mehnert, Jacqueline Rucker, Brigitte Nixdorf, Samuel Cirés, Franziska Leunert, Klaus Jöhnk, Claudia WiednerAbstract:Some tropical cyanobacteria spread to temperate freshwaters during the last decades. To evaluate their further development in temperate lakes we studied the temperature- and light-dependent growth of three invasive (Cylindrospermopsis raciborskii, Anabaena bergii, Aphanizomenon aphanizomenoides) and three native (Aphanizomenon gracile, Aphanizomenon flos-aquae, Anabaena macrospora) cyanobacterial species (Nostocales) from German lakes. We also included one potentially invasive (Aphanizomenon ovalisporum) Nostocales species. We conducted semi-continuous culture experiments and a microcosm experiment along a natural light gradient. Temperature data were used to design a model to simulate the development of selected species according to three temperature scenarios (past, present and future). Native species had significantly higher growth rates than invasive species and the potential invader A. ovalisporum at low temperatures (≤ 10°C), while the opposite was true at high temperatures (≥ 35°C). Maximum growth rates of A. ovalisporum, A. aphanizomenoides and C. raciborskii were clearly higher than those of A. bergii and the native species. Regarding light-dependent growth, significant differences were found between single species but not between all native and invasive species. The model simulation demonstrates a shift in dominance from the native A. gracile in the historic scenario to C. raciborskii populations in the future scenario, in which also the potential invader A. ovalisporum is able to establish populations in temperate lakes. Our findings suggest that any further temperature increase would promote the growth and development of Nostocales species in general, and that of the invasive species in particular, and would enable a more northward expansion of A. ovalisporum.
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Competitiveness of invasive and native cyanobacteria from temperate freshwaters under various light and temperature conditions
Journal of Plankton Research, 2010Co-Authors: Grit Mehnert, Jacqueline Rucker, Brigitte Nixdorf, Samuel Cirés, Franziska Leunert, Klaus Jöhnk, Claudia WiednerAbstract:Some tropical cyanobacteria have spread to temperate freshwaters during the last decades. To evaluate their further development in temperate lakes, we studied the temperature- and light-dependent growth of three invasive (Cylindrospermopsis raciborskii, Anabaena bergii and Aphanizomenon aphanizomenoides) and three native (Aphanizomenon gracile, Aphanizomenon flos-aquae and Anabaena macrospora) cyanobacterial species (Nostocales) from German lakes. We also included one potentially invasive (Aphanizomenon ovalisporum) Nostocales species. We conducted semi-continuous culture experiments and a microcosm experiment along a natural light gradient. Temperature data were used to design a model to simulate the development of selected species according to three temperature scenarios (past, present and future). Native species had significantly higher growth rates than invasive species and the potential invader A. ovalisporum at low temperatures (� 108C), while the opposite was true at high temperatures (� 358C). Maximum growth rates of A. ovalisporum, A. aphanizomenoides and C. raciborskii were clearly higher than those of A. bergii and the native species. Regarding light-dependent growth, significant differences were found between single species but not between all native and invasive species. The model simulation demonstrates a shift in dominance from the native A. gracile in the historic scenario to C. raciborskii populations in the future scenario, in which also the potential invader A. ovalisporum is able to establish populations in temperate lakes. Our findings suggest that any further temperature increase would promote the growth and development of Nostocales species in general, and that of the invasive species in particular, and would enable a more northward expansion of A. ovalisporum.
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concentrations of particulate and dissolved cylindrospermopsin in 21 aphanizomenon dominated temperate lakes
Toxicon, 2007Co-Authors: Jacqueline Rucker, Anke Stuken, Ingrid Chorus, Brigitte Nixdorf, Jutta Fastner, Claudia WiednerAbstract:Abstract The cyanobacterial toxin cylindrospermopsin (CYN) is widely distributed in German lakes, but volumetric data for risk assessment are lacking and it is unclear which cyanobacterial species produce CYN in Europe. We therefore analyzed CYN concentration and cyanobacterial composition of 21 German lakes in 2005. CYN was detected in 19 lakes (102 of 115 samples). In total, 45 samples contained particulate CYN only, and 57 contained both dissolved and particulate CYN. The concentrations were 0.002–0.484 μg L−1 for particulate CYN and 0.08–11.75 μg L−1 for dissolved CYN with a maximum of 12.1 μg L−1 total CYN. A drinking water guideline value of 1 μg L−1 proposed by Humpage and Falconer [2003. Oral toxicity of the cyanobacterial toxin CYN in male Swiss albino mice: determination of no observed adverse effect level for deriving a drinking water guideline value. Environ. Toxicol. 18, 94–103] was exceeded in 18 samples from eight lakes due to high concentrations of dissolved CYN. CYN occurrence in the German lakes could not be ascribed to the three known CYN-producing species Cylindrospermopsis raciborskii, Anabaena bergii and Aphanizomenon flos-aquae, which were detected in some lakes in low abundances. The highest correlation coefficients were observed between particulate CYN and the native Aphanizomenon gracile. It occurred in 98 CYN-positive samples, was the most abundant Nostocales and was the only Nostocales in five samples. This indicates that A. gracile is a potential CYN producer in German lakes.
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occurrence of the cyanobacterial toxin cylindrospermopsin in northeast germany
Environmental Toxicology, 2007Co-Authors: Jutta Fastner, Anke Stuken, Ingrid Chorus, Jacqueline Rucker, Karina Preussel, Brigitte Nixdorf, Antje Kohler, Claudia WiednerAbstract:Received 15 February 2006; revised 12 June 2006; accepted 20 July 2006ABSTRACT: The frequent occurrence of the cyanobacterial toxin cylindrospermopsin (CYN) in the (sub)-tropics has been largely associated with cyanobacteria of the order Nostocales of tropical origin, in partic-ular Cylindrospermopsis raciborskii. C. raciborskii is currently observed to spread northwards into temper-ate climatic zones. In addition, further cyanobacteria of the order Nostocales typically inhabiting waterbodies in temperate regions are being identified as CYN-producers. Therefore, data on the distribution ofCYN in temperate regions are necessary for a first assessment of potential risks due to CYN in water usedfor drinking and recreation. A total of 127 lakes situated in the north-eastern part of Germany were investi-gated in 2004 for the presence of the toxin CYN and the phytoplankton composition. The toxin could bedetected in half of the lakes (n ¼ 63) and in half of 165 samples (n ¼ 88). Concentrations reached up to73.2 g CYN/g DW. CYN thus proved more widely distributed than previously demonstrated. The analysesof phytoplankton data suggest Aphanizomenon sp. and Anabaena sp. as important CYN producers inGermany, and confirm recent findings of Aphanizomenon flos-aquae as CYN-producing species fre-quently inhabiting water bodies in temperate climatic regions. The data shown here suggest that CYNmay be an important cyanobacterial toxin in German water bodies and that further data are needed toassess this.
Samuel Cirés - One of the best experts on this subject based on the ideXlab platform.
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phylogeography of cylindrospermopsin and paralytic shellfish toxin producing Nostocales cyanobacteria from mediterranean europe spain
Applied and Environmental Microbiology, 2014Co-Authors: Samuel Cirés, Ramsy Agha, Andreas Ballot, David Velázquez, Mar Ia Cristina CaseroAbstract:Planktonic Nostocales cyanobacteria represent a challenge for microbiological research because of the wide range of cyanotoxins that they synthesize and their invasive behavior, which is presumably enhanced by global warming. To gain insight into the phylogeography of potentially toxic Nostocales from Mediterranean Europe, 31 strains of Anabaena (Anabaena crassa, A. lemmermannii, A. mendotae, and A. planctonica), Aphanizomenon (Aphanizomenon gracile, A. ovalisporum), and Cylindrospermopsis raciborskii were isolated from 14 freshwater bodies in Spain and polyphasically analyzed for their phylogeography, cyanotoxin production, and the presence of cyanotoxin biosynthesis genes. The potent cytotoxin cylindrospermopsin (CYN) was produced by all 6 Aphanizomenon ovalisporum strains at high levels (5.7 to 9.1 μg CYN mg−1 [dry weight]) with low variation between strains (1.5 to 3.9-fold) and a marked extracellular release (19 to 41% dissolved CYN) during exponential growth. Paralytic shellfish poisoning (PSP) neurotoxins (saxitoxin, neosaxitoxin, and decarbamoylsaxitoxin) were detected in 2 Aphanizomenon gracile strains, both containing the sxtA gene. This gene was also amplified in non-PSP toxin-producing Aphanizomenon gracile and Aphanizomenon ovalisporum. Phylogenetic analyses supported the species identification and confirmed the high similarity of Spanish Anabaena and Aphanizomenon strains with other European strains. In contrast, Cylindrospermopsis raciborskii from Spain grouped together with American strains and was clearly separate from the rest of the European strains, raising questions about the current assumptions of the phylogeography and spreading routes of C. raciborskii. The present study confirms that the nostocalean genus Aphanizomenon is a major source of CYN and PSP toxins in Europe and demonstrates the presence of the sxtA gene in CYN-producing Aphanizomenon ovalisporum.
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Overwintering populations of Anabaena, Aphanizomenon and Microcystis as potential inocula for summer blooms
Journal of Plankton Research, 2013Co-Authors: Samuel Cirés, Ramsy Agha, Lars Wörmer, Antonio QuesadaAbstract:Overwintering cyanobacterial populations of Nostocales and Microcystis were investigated in six freshwater reservoirs in Northwestern Spain during two consecutive winters. Surface sediments hosted 10–10 akinetes mL and 10–10 Microcystis colonies mL. Sediments from deeper areas close to dam accumulated 2-fold (Microcystis) and 11-fold (akinetes) greater concentrations than those at the shallower upstream areas. Anabaena spp. and Microcystis aeruginosa dominated the sediment pool, with minor amounts of akinetes of Aphanizomenon (Aph. flos-aquae, Aph. gracile) and benthic Nostocales (Cylindrospermum, Nostoc and Trichormus). Our study confirms the dual benthic-pelagic overwintering of Anabaena, Aphanizomenon and Microcystis, found in the pelagial at 7.5–9.88C. This study also provides an insight into the little known annual cycle of potential cyanotoxin-producers Aph. gracile and Anabaena circinalis. Our estimates show that: (i) only a small fraction (,1%) of the sediment pool of akinetes and Microcystis was resupended in the bottom water during winter which, however, may be sufficient inocula to build up the summer maxima under realistic in situ growth rates; and (ii) the time required for the development of summer populations is mainly driven by growth rates, and therefore by the environmental conditions faced by the inoculum, with a lower influence (although greater for Microcystis than for Nostocales) of the inoculum size.
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Competitiveness of invasive and native cyanobacteria from temperate freshwaters under various light and temperature conditions
Journal of Plankton Research, 2010Co-Authors: Grit Mehnert, Jacqueline Rucker, Brigitte Nixdorf, Samuel Cirés, Franziska Leunert, Klaus Jöhnk, Claudia WiednerAbstract:Some tropical cyanobacteria spread to temperate freshwaters during the last decades. To evaluate their further development in temperate lakes we studied the temperature- and light-dependent growth of three invasive (Cylindrospermopsis raciborskii, Anabaena bergii, Aphanizomenon aphanizomenoides) and three native (Aphanizomenon gracile, Aphanizomenon flos-aquae, Anabaena macrospora) cyanobacterial species (Nostocales) from German lakes. We also included one potentially invasive (Aphanizomenon ovalisporum) Nostocales species. We conducted semi-continuous culture experiments and a microcosm experiment along a natural light gradient. Temperature data were used to design a model to simulate the development of selected species according to three temperature scenarios (past, present and future). Native species had significantly higher growth rates than invasive species and the potential invader A. ovalisporum at low temperatures (≤ 10°C), while the opposite was true at high temperatures (≥ 35°C). Maximum growth rates of A. ovalisporum, A. aphanizomenoides and C. raciborskii were clearly higher than those of A. bergii and the native species. Regarding light-dependent growth, significant differences were found between single species but not between all native and invasive species. The model simulation demonstrates a shift in dominance from the native A. gracile in the historic scenario to C. raciborskii populations in the future scenario, in which also the potential invader A. ovalisporum is able to establish populations in temperate lakes. Our findings suggest that any further temperature increase would promote the growth and development of Nostocales species in general, and that of the invasive species in particular, and would enable a more northward expansion of A. ovalisporum.
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Competitiveness of invasive and native cyanobacteria from temperate freshwaters under various light and temperature conditions
Journal of Plankton Research, 2010Co-Authors: Grit Mehnert, Jacqueline Rucker, Brigitte Nixdorf, Samuel Cirés, Franziska Leunert, Klaus Jöhnk, Claudia WiednerAbstract:Some tropical cyanobacteria have spread to temperate freshwaters during the last decades. To evaluate their further development in temperate lakes, we studied the temperature- and light-dependent growth of three invasive (Cylindrospermopsis raciborskii, Anabaena bergii and Aphanizomenon aphanizomenoides) and three native (Aphanizomenon gracile, Aphanizomenon flos-aquae and Anabaena macrospora) cyanobacterial species (Nostocales) from German lakes. We also included one potentially invasive (Aphanizomenon ovalisporum) Nostocales species. We conducted semi-continuous culture experiments and a microcosm experiment along a natural light gradient. Temperature data were used to design a model to simulate the development of selected species according to three temperature scenarios (past, present and future). Native species had significantly higher growth rates than invasive species and the potential invader A. ovalisporum at low temperatures (� 108C), while the opposite was true at high temperatures (� 358C). Maximum growth rates of A. ovalisporum, A. aphanizomenoides and C. raciborskii were clearly higher than those of A. bergii and the native species. Regarding light-dependent growth, significant differences were found between single species but not between all native and invasive species. The model simulation demonstrates a shift in dominance from the native A. gracile in the historic scenario to C. raciborskii populations in the future scenario, in which also the potential invader A. ovalisporum is able to establish populations in temperate lakes. Our findings suggest that any further temperature increase would promote the growth and development of Nostocales species in general, and that of the invasive species in particular, and would enable a more northward expansion of A. ovalisporum.
Assaf Sukenik - One of the best experts on this subject based on the ideXlab platform.
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Dormant Cells (Akinetes) of Filamentous Cyanobacteria Demonstrate a Great Variability in Morphology, Physiology, and Ecological Function
Cyanobacteria, 2019Co-Authors: Assaf Sukenik, Jacqueline Rucker, Iris MaldenerAbstract:Abstract Akinetes are dormant cells of cyanobacteria species from the Nostocales and Stigonematales orders, allowing these phototrophic bacteria to survive in harsh and starvation conditions. These spore-like thick-walled, nonmotile cells differentiate from vegetative cells in response to environmental fluctuations. They serve a perennating role as they maintain the ability to resume the morphology and functions of vegetative cells including the renewal of cell division after a long period of dormancy. Here, we review recent advances in studies of akinetes emphasizing environmental triggers, cellular responses, morphological, and structural changes that occur during akinete differentiation and germination. Variations in akinete formation, structure, and metabolism among different species are highlighted and their role in bloom formation of Nostocales species is demonstrated.
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Deciphering the mechanisms against oxidative stress in developing and mature akinetes of the cyanobacterium Aphanizomenon ovalisporum.
Microbiology (Reading England), 2015Co-Authors: Ruth N. Kaplan-levy, Ora Hadas, Assaf SukenikAbstract:Cells of filamentous cyanobacteria of the orders Nostocales and Stigonematales can differentiate into dormant forms called akinetes. Akinetes play a key role in the survival, abundance and distribution of the species, contributing an inoculum for their perennial blooms. In the cyanobacterium Aphanizomenon ovalisporum, potassium deficiency triggers the formation of akinetes. Here we present experimental evidence for the production of reactive oxygen species (ROS) during akinete development in response to potassium deficiency. The function of ROS as a primer signal for akinete differentiation was negated. Nevertheless, akinetes acquired protective mechanisms against oxidative damage during their differentiation and maintained them as they matured, giving akinetes advantages enabling survival in harsh conditions.
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A CARD-FISH protocol for the identification and enumeration of cyanobacterial akinetes in lake sediments.
FEMS microbiology ecology, 2012Co-Authors: Jessica Ramm, Jacqueline Rucker, Claudia Wiedner, Andreas Ballot, Ora Hadas, Achsa Lupu, Assaf SukenikAbstract:Akinetes are the dormant cells of Nostocales (cyanobacteria) that enable the organisms to survive harsh environmental conditions while resting in bottom sediments. The germination of akinetes assists the dispersal and persistence of the species. The assessment of the akinete pool in lake sediments is essential to predict the bloom formation of the Nostocales population. We present here the implementation of an improved catalysed reporter deposition (CARD)–fluorescence in situ hybridization (FISH) protocol to assist the identification and quantification of akinetes in sediment samples. Several 16S rRNA gene oligonucleotide probes were evaluated for labelling akinetes of various species of Anabaena, Aphanizomenon and Cylindrospermopsis. Akinetes of all the taxa studied were successfully labelled and could be easily detected by their bright fluorescence signal. The probes' specificity was tested with 32 strains of different taxa. All six Cylindrospermopsis raciborskii strains were labelled with a specific probe for its 16S rRNA gene. A more general probe labelled 73% of the Anabaena and Aphanizomenon strains. The counting data of field samples obtained with CARD-FISH and the regular light microscopy approach did not differ significantly, confirming the suitability of both methods. The CARD-FISH approach was found to be less time-consuming because of better visibility of akinetes.
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Appearance and establishment of diazotrophic cyanobacteria in Lake Kinneret, Israel
Freshwater Biology, 2012Co-Authors: Ora Hadas, A. Nishri, Aaron Kaplan, Riki Pinkas, N. Malinsky-rushansky, A. Rimmer, Assaf SukenikAbstract:Summary 1. We propose that the appearance and establishment of Nostocales (cyanobacteria) species of the genera Aphanizomenon and Cylindrospermopsis in the warm subtropical Lake Kinneret (Sea of Galilee, Israel) from 1994 was linked to changes in climate conditions and summer nitrogen (N) availability. 2. From 1994 to 2009, an increase in frequency of events of elevated water temperature (>29 °C) in summer, and to some extent a greater frequency of lower summer wind speed events, affected water turbulence and water column stratification, thus providing better physical conditions for the establishment of these populations. 3. In recent years, N-depleted conditions in Lake Kinneret in early summer have promoted the development and domination of Nostocales that could gain an ecological advantage owing to their N2-fixing capability. 4. Nitrogen fixation rates coincided both with heterocyst abundance and with Nostocales biomass. The N supplied to the lake via nitrogen fixation ranged from negligible quantities when Nostocales represented only a minor component of the phytoplankton community to 123 tonnes when Cylindrospermopsis bloomed in 2005. This high N2 fixation rate equals the average summer dissolved inorganic nitrogen load to the lake via the Jordan River.
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Invasion of Nostocales (cyanobacteria) to Subtropical and Temperate Freshwater Lakes - Physiological, Regional, and Global Driving Forces.
Frontiers in microbiology, 2012Co-Authors: Assaf Sukenik, Aaron Kaplan, Ora Hadas, Antonio QuesadaAbstract:Similar to the increased number of studies on invasive plants and animals in terrestrial and aquatic ecosystems, many reports were recently published on the invasion of Nostocales (cyanobacteria) to freshwater environments worldwide. Invasion and proliferation of Nostocales in new habitats have the potential to significantly alter the structure of the native community and to modify ecosystem functioning. But most importantly, they influence the water quality due to a variety of toxic compounds that some species produce. Therefore a special attention was given to the invasion and persistence of toxic cyanobacteria in many aquatic ecosystems. Here we summarize the currently published records on the invasion of two Nostocales genera, Cylindrospermopsis and Aphanizomenon, to lakes and water reservoirs in subtropical and temperate zones. These invading species possess traits thought to be common to many invasive organisms: high growth rate, high resource utilization efficiency and overall superior competitive abilities over native species when local conditions vary. Assuming that dispersion routes of cyanobacteria have not been changed much in recent decades, their recent establishment and proliferation in new habitats indicate changes in the environment under which they can exploit their physiological advantage over the native phytoplankton population. In many cases, global warming was identified as the major driving force for the invasion of Nostocales. Due to this uncontrollable trend, invasive Nostocales species are expected to maintain their presence in new habitats and further expand to new environments. In other cases, regional changes in nutrient loads and in biotic conditions were attributed to the invasion events.
