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Nina Lundholm - One of the best experts on this subject based on the ideXlab platform.
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impacts of ocean acidification on growth and toxin content of the marine diatoms pseudo nitzschia australis and p fraudulenta
Marine Environmental Research, 2021Co-Authors: Nour Ayache, Nina Lundholm, Frederik Gai, Fabienne Herve, Zouher Amzil, Amandine M N CaruanaAbstract:Abstract This paper present the effects of ocean acidification on growth and domoic acid (DA) content of several strains of the toxic Pseudo-Nitzschia australis and the non-toxic P. fraudulenta. Three strains of each species (plus two subclones of P. australis) were acclimated and grown in semi-continuous cultures at three pH levels: 8.07, 7.77, and 7.40, in order to simulate changes of seawater pH from present to plausible future levels. Our results showed that lowering pH from current level (8.07) to predicted pH level in 2100 (7.77) did not affect the mean growth rates of some of the P. australis strains (FR-PAU-17 and L3-100), but affected other strains either negatively (L3-30) or positively (L3.4). However, the growth rates significantly decreased with pH lowered to 7.40 (by 13% for L3-100, 43% for L3-30 and 16% for IFR-PAU-17 compared to the rates at pH 8.07). In contrast, growth rates of the non-toxic P. fraudulenta strains were not affected by pH changing from 8.07 to 7.40. The P. australis strains produced DA at all pH levels tested, and the highest particulate DA concentration normalized to cell abundance (pDA) was found at pH 8.07. Total DA content (pDA and dissolved DA) was significantly higher at current pH (8.07) compared to pH (7.77), exept for one strain (L 3.4) where no difference was found. At lower pH levels 7.77–7.40, total DA content was similar, except for strains IFR-PAU-17 and L3-100 which had the lowest content at the pH 7.77. The diversity in the responses in growth and DA content highlights the inter- and intra-specific variation in Pseudo-Nitzschia species in response to ocean acidification. When exploring environmental responses of Pseudo-Nitzschia using cultured cells, not only strain-specific variation but also culturing history should be taken into consideration, as the light levels under which the subclones were cultured, afterwards affected both maximum growth rates and DA content.
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Seasonal plankton succession is in accordance with phycotoxin occurrence in Disko Bay, West Greenland.
Harmful Algae, 2021Co-Authors: Claudia Sabine Bruhn, Bernd Krock, Nina Lundholm, Sylke Wohlrab, Uwe JohnAbstract:Abstract Harmful algal blooms (HABs) are occurring more frequently in the world's oceans, probably as a consequence of climate change. HABs have not been considered a serious concern in the Arctic, even though the Arctic warms faster than any other region. While phycotoxins and toxin-producing phytoplankton have been found in Arctic waters on several occasions, there is a lack of information on seasonal succession of species and whether the occurrence of harmful species correlates with the presence of their respective phycotoxins. Hence, there is no baseline to assess future changes of HABs in this area. Here, we investigated two periods, from winter to spring and from the spring bloom until summer, in Disko Bay, West Greenland and followed the succession of toxins and their producers using metabarcoding, as well as analyses of particulate and dissolved toxins. We observed a typical seasonal succession with a spring bloom dominated by diatoms, followed by dinoflagellates in summer, with the two most important potentially toxic taxa found being Pseudo-Nitzschia spp. and Alexandrium ostenfeldii. The Pseudo-Nitzschia spp. peak correlated with a clear increase in particulate domoic acid, reaching 0.05 pg/L. Presence of Alexandrium ostenfeldii could be linked to an increase in spirolides, up to 56.4 pg/L in the particulate phase. Generally, the majority of detected dissolved toxins followed the succession pattern of the particulate toxins with a delay in time. Our results further show that Arctic waters are a suitable habitat for various toxin producers and that the strong seasonality of this environment is reflected by changing abundances of different toxins that pose a potential threat to the ecosystem and its beneficiaries.
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Transcriptomic responses to grazing reveal the metabolic pathway leading to the biosynthesis of domoic acid and highlight different defense strategies in diatoms
BMC Molecular Biology, 2019Co-Authors: Sara Harðardóttir, Bernd Krock, Sylke Wohlrab, Ditte Marie Hjort, Torkel Gissel Nielsen, Uwe John, Nina LundholmAbstract:Background A major cause of phytoplankton mortality is predation by zooplankton. Strategies to avoid grazers have probably played a major role in the evolution of phytoplankton and impacted bloom dynamics and trophic energy transport. Certain species of the genus Pseudo-Nitzschia produce the neurotoxin, domoic acid (DA), as a response to the presence of copepod grazers, suggesting that DA is a defense compound. The biosynthesis of DA comprises fusion of two precursors, a C10 isoprenoid geranyl pyrophosphate and l -glutamate. Geranyl pyrophosphate (GPP) may derive from the mevalonate isoprenoid (MEV) pathway in the cytosol or from the methyl-erythritol phosphate (MEP) pathway in the plastid. l -glutamate is suggested to derive from the citric acid cycle. Fragilariopsis , a phylogenetically related but nontoxic genus of diatoms, does not appear to possess a similar defense mechanism. We acquired information on genes involved in biosynthesis, precursor pathways and regulatory functions for DA production in the toxigenic Pseudo-Nitzschia seriata , as well as genes involved in responses to grazers to resolve common responses for defense strategies in diatoms. Results Several genes are expressed in cells of Pseudo-Nitzschia when these are exposed to predator cues. No genes are expressed in Fragilariopsis when treated similarly, indicating that the two taxa have evolved different strategies to avoid predation. Genes involved in signal transduction indicate that Pseudo-Nitzschia cells receive signals from copepods that transduce cascading molecular precursors leading to the formation of DA. Five out of seven genes in the MEP pathway for synthesis of GPP are upregulated, but none in the conventional MEV pathway. Five genes with known or suggested functions in later steps of DA formation are upregulated. We conclude that no gene regulation supports that l -glutamate derives from the citric acid cycle, and we suggest the proline metabolism to be a downstream precursor. Conclusions Pseudo-Nitzschia cells, but not Fragilariopsis , receive and respond to copepod cues. The cellular route for the C10 isoprenoid product for biosynthesis of DA arises from the MEP metabolic pathway and we suggest proline metabolism to be a downstream precursor for l -glutamate. We suggest 13 genes with unknown function to be involved in diatom responses to grazers.
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dangerous relations in the arctic marine food web interactions between toxin producing pseudo nitzschia diatoms and calanus copepodites
Marine Drugs, 2015Co-Authors: Sara Harðardóttir, Bernd Krock, Torkel Gissel Nielsen, Anna Tammilehto, Eva Friis Moller, Marina Pancic, Nina LundholmAbstract:Diatoms of the genus Pseudo-Nitzschia produce domoic acid (DA), a toxin that is vectored in the marine food web, thus causing serious problems for marine organisms and humans. In spite of this, knowledge of interactions between grazing zooplankton and diatoms is restricted. In this study, we examined the interactions between Calanus copepodites and toxin producing Pseudo-Nitzschia. The copepodites were fed with different concentrations of toxic P. seriata and a strain of P. obtusa that previously was tested to be non-toxic. The ingestion rates did not differ among the diets (P. seriata, P. obtusa, a mixture of both species), and they accumulated 6%–16% of ingested DA (up to 420 µg per dry weight copepodite). When P. seriata was exposed to the copepodites, either through physical contact with the grazers or separated by a membrane, the toxicity of P. seriata increased (up to 3300%) suggesting the response to be chemically mediated. The induced response was also triggered when copepodites grazed on another diatom, supporting the hypothesis that the cues originate from the copepodite. Neither pH nor nutrient concentrations explained the induced DA production. Unexpectedly, P. obtusa also produced DA when exposed to grazing copepodites, thus representing the second reported toxic polar diatom.
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induction of domoic acid production in the toxic diatom pseudo nitzschia seriata by calanoid copepods
Aquatic Toxicology, 2015Co-Authors: Anna Tammilehto, Bernd Krock, Torkel Gissel Nielsen, Eva Friis Moller, Nina LundholmAbstract:The toxic diatom Pseudo-Nitzschia seriata was exposed directly and indirectly (separated by a membrane) to copepods, Calanus hyperboreus and C. finmarchicus, to evaluate the effects of the copepods on domoic acid production and chain formation in P. seriata. The toxicity of P. seriata increased in the presence of the copepods. This response was chemically mediated without physical contact between the organisms suggesting that it was induced by potential waterborne cues from the copepods or changes in water chemistry. Domoic acid production may be related to defense against grazing in P. seriata although it was not shown in the present study. To evaluate if the induction of domoic acid production was mediated by the chemical cues from damaged P. seriata cells, live P. seriata cells were exposed to a P. seriata cell homogenate, but no effect was observed. Chain formation in P. seriata was affected only when in direct contact with the copepods. This study suggests that the presence of zooplankton may be one of the factors affecting the toxicity of Pseudo-Nitzschia blooms in the field.
Bernd Krock - One of the best experts on this subject based on the ideXlab platform.
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Seasonal plankton succession is in accordance with phycotoxin occurrence in Disko Bay, West Greenland.
Harmful Algae, 2021Co-Authors: Claudia Sabine Bruhn, Bernd Krock, Nina Lundholm, Sylke Wohlrab, Uwe JohnAbstract:Abstract Harmful algal blooms (HABs) are occurring more frequently in the world's oceans, probably as a consequence of climate change. HABs have not been considered a serious concern in the Arctic, even though the Arctic warms faster than any other region. While phycotoxins and toxin-producing phytoplankton have been found in Arctic waters on several occasions, there is a lack of information on seasonal succession of species and whether the occurrence of harmful species correlates with the presence of their respective phycotoxins. Hence, there is no baseline to assess future changes of HABs in this area. Here, we investigated two periods, from winter to spring and from the spring bloom until summer, in Disko Bay, West Greenland and followed the succession of toxins and their producers using metabarcoding, as well as analyses of particulate and dissolved toxins. We observed a typical seasonal succession with a spring bloom dominated by diatoms, followed by dinoflagellates in summer, with the two most important potentially toxic taxa found being Pseudo-Nitzschia spp. and Alexandrium ostenfeldii. The Pseudo-Nitzschia spp. peak correlated with a clear increase in particulate domoic acid, reaching 0.05 pg/L. Presence of Alexandrium ostenfeldii could be linked to an increase in spirolides, up to 56.4 pg/L in the particulate phase. Generally, the majority of detected dissolved toxins followed the succession pattern of the particulate toxins with a delay in time. Our results further show that Arctic waters are a suitable habitat for various toxin producers and that the strong seasonality of this environment is reflected by changing abundances of different toxins that pose a potential threat to the ecosystem and its beneficiaries.
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Transcriptomic responses to grazing reveal the metabolic pathway leading to the biosynthesis of domoic acid and highlight different defense strategies in diatoms
BMC Molecular Biology, 2019Co-Authors: Sara Harðardóttir, Bernd Krock, Sylke Wohlrab, Ditte Marie Hjort, Torkel Gissel Nielsen, Uwe John, Nina LundholmAbstract:Background A major cause of phytoplankton mortality is predation by zooplankton. Strategies to avoid grazers have probably played a major role in the evolution of phytoplankton and impacted bloom dynamics and trophic energy transport. Certain species of the genus Pseudo-Nitzschia produce the neurotoxin, domoic acid (DA), as a response to the presence of copepod grazers, suggesting that DA is a defense compound. The biosynthesis of DA comprises fusion of two precursors, a C10 isoprenoid geranyl pyrophosphate and l -glutamate. Geranyl pyrophosphate (GPP) may derive from the mevalonate isoprenoid (MEV) pathway in the cytosol or from the methyl-erythritol phosphate (MEP) pathway in the plastid. l -glutamate is suggested to derive from the citric acid cycle. Fragilariopsis , a phylogenetically related but nontoxic genus of diatoms, does not appear to possess a similar defense mechanism. We acquired information on genes involved in biosynthesis, precursor pathways and regulatory functions for DA production in the toxigenic Pseudo-Nitzschia seriata , as well as genes involved in responses to grazers to resolve common responses for defense strategies in diatoms. Results Several genes are expressed in cells of Pseudo-Nitzschia when these are exposed to predator cues. No genes are expressed in Fragilariopsis when treated similarly, indicating that the two taxa have evolved different strategies to avoid predation. Genes involved in signal transduction indicate that Pseudo-Nitzschia cells receive signals from copepods that transduce cascading molecular precursors leading to the formation of DA. Five out of seven genes in the MEP pathway for synthesis of GPP are upregulated, but none in the conventional MEV pathway. Five genes with known or suggested functions in later steps of DA formation are upregulated. We conclude that no gene regulation supports that l -glutamate derives from the citric acid cycle, and we suggest the proline metabolism to be a downstream precursor. Conclusions Pseudo-Nitzschia cells, but not Fragilariopsis , receive and respond to copepod cues. The cellular route for the C10 isoprenoid product for biosynthesis of DA arises from the MEP metabolic pathway and we suggest proline metabolism to be a downstream precursor for l -glutamate. We suggest 13 genes with unknown function to be involved in diatom responses to grazers.
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domoic acid in a marine pelagic food web exposure of southern right whales eubalaena australis to domoic acid on the peninsula valdes calving ground argentina
Harmful Algae, 2017Co-Authors: Valeria C Dagostino, Norma Santinelli, Viviana Sastre, Mariana Degrati, Bernd Krock, Torben Krohn, Silvana Laura Dans, Mónica Susana HoffmeyerAbstract:The gulfs that surround Peninsula Valdes (PV), Golfo Nuevo and Golfo San Jose in Argentina, are important calving grounds for the southern right whale Eubalaena australis. However, high calf mortality events in recent years could be associated with phycotoxin exposure. The present study evaluated the transfer of domoic acid (DA) from Pseudo-Nitzschia spp., potential producers of DA, to living and dead right whales via zooplanktonic vectors, while the whales are on their calving ground at PV. Phytoplankton and mesozooplankton (primary prey of the right whales at PV and potential grazers of Pseudo-Nitzschia cells) were collected during the 2015 whale season and analyzed for species composition and abundance. DA was measured in plankton and fecal whale samples (collected during whale seasons 2013, 2014 and 2015) using liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS). The genus Pseudo-Nitzschia was present in both gulfs with abundances ranging from 4.4 x 102 and 4.56 x 105 cell l -1. Pseudo-Nitzschia australis had the highest abundance with up to 4.56 x 105 cell l-1. DA in phytoplankton was generally low, with the exception of samples collected during a P. australis bloom. No clear correlation was found between DA in phytoplankton and mesozooplankton samples. The predominance of copepods in mesozooplankton samples indicates that they were the primary vector for the transfer of DA from Pseudo-Nitzschia spp. to higher trophic levels. High levels of DA were detected in four whale fecal samples (ranging from 0.30 to 710 mg g-1 dry weight of fecal sample or from 0.05 and 113.6 mg g-1 wet weight assuming a mean water content of 84%). The maximum level of DA detected in fecal samples (710 mg DA g-1 dry weight of fecal sample) is the highest reported in southern right whales to date. The current findings demonstrate for the first time that southern right whales, E. australis, are exposed to DA via copepods as vectors during their calving season in the gulfs of PV.
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dangerous relations in the arctic marine food web interactions between toxin producing pseudo nitzschia diatoms and calanus copepodites
Marine Drugs, 2015Co-Authors: Sara Harðardóttir, Bernd Krock, Torkel Gissel Nielsen, Anna Tammilehto, Eva Friis Moller, Marina Pancic, Nina LundholmAbstract:Diatoms of the genus Pseudo-Nitzschia produce domoic acid (DA), a toxin that is vectored in the marine food web, thus causing serious problems for marine organisms and humans. In spite of this, knowledge of interactions between grazing zooplankton and diatoms is restricted. In this study, we examined the interactions between Calanus copepodites and toxin producing Pseudo-Nitzschia. The copepodites were fed with different concentrations of toxic P. seriata and a strain of P. obtusa that previously was tested to be non-toxic. The ingestion rates did not differ among the diets (P. seriata, P. obtusa, a mixture of both species), and they accumulated 6%–16% of ingested DA (up to 420 µg per dry weight copepodite). When P. seriata was exposed to the copepodites, either through physical contact with the grazers or separated by a membrane, the toxicity of P. seriata increased (up to 3300%) suggesting the response to be chemically mediated. The induced response was also triggered when copepodites grazed on another diatom, supporting the hypothesis that the cues originate from the copepodite. Neither pH nor nutrient concentrations explained the induced DA production. Unexpectedly, P. obtusa also produced DA when exposed to grazing copepodites, thus representing the second reported toxic polar diatom.
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induction of domoic acid production in the toxic diatom pseudo nitzschia seriata by calanoid copepods
Aquatic Toxicology, 2015Co-Authors: Anna Tammilehto, Bernd Krock, Torkel Gissel Nielsen, Eva Friis Moller, Nina LundholmAbstract:The toxic diatom Pseudo-Nitzschia seriata was exposed directly and indirectly (separated by a membrane) to copepods, Calanus hyperboreus and C. finmarchicus, to evaluate the effects of the copepods on domoic acid production and chain formation in P. seriata. The toxicity of P. seriata increased in the presence of the copepods. This response was chemically mediated without physical contact between the organisms suggesting that it was induced by potential waterborne cues from the copepods or changes in water chemistry. Domoic acid production may be related to defense against grazing in P. seriata although it was not shown in the present study. To evaluate if the induction of domoic acid production was mediated by the chemical cues from damaged P. seriata cells, live P. seriata cells were exposed to a P. seriata cell homogenate, but no effect was observed. Chain formation in P. seriata was affected only when in direct contact with the copepods. This study suggests that the presence of zooplankton may be one of the factors affecting the toxicity of Pseudo-Nitzschia blooms in the field.
Mónica Susana Hoffmeyer - One of the best experts on this subject based on the ideXlab platform.
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domoic acid in a marine pelagic food web exposure of southern right whales eubalaena australis to domoic acid on the peninsula valdes calving ground argentina
Harmful Algae, 2017Co-Authors: Valeria C Dagostino, Norma Santinelli, Viviana Sastre, Mariana Degrati, Bernd Krock, Torben Krohn, Silvana Laura Dans, Mónica Susana HoffmeyerAbstract:The gulfs that surround Peninsula Valdes (PV), Golfo Nuevo and Golfo San Jose in Argentina, are important calving grounds for the southern right whale Eubalaena australis. However, high calf mortality events in recent years could be associated with phycotoxin exposure. The present study evaluated the transfer of domoic acid (DA) from Pseudo-Nitzschia spp., potential producers of DA, to living and dead right whales via zooplanktonic vectors, while the whales are on their calving ground at PV. Phytoplankton and mesozooplankton (primary prey of the right whales at PV and potential grazers of Pseudo-Nitzschia cells) were collected during the 2015 whale season and analyzed for species composition and abundance. DA was measured in plankton and fecal whale samples (collected during whale seasons 2013, 2014 and 2015) using liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS). The genus Pseudo-Nitzschia was present in both gulfs with abundances ranging from 4.4 x 102 and 4.56 x 105 cell l -1. Pseudo-Nitzschia australis had the highest abundance with up to 4.56 x 105 cell l-1. DA in phytoplankton was generally low, with the exception of samples collected during a P. australis bloom. No clear correlation was found between DA in phytoplankton and mesozooplankton samples. The predominance of copepods in mesozooplankton samples indicates that they were the primary vector for the transfer of DA from Pseudo-Nitzschia spp. to higher trophic levels. High levels of DA were detected in four whale fecal samples (ranging from 0.30 to 710 mg g-1 dry weight of fecal sample or from 0.05 and 113.6 mg g-1 wet weight assuming a mean water content of 84%). The maximum level of DA detected in fecal samples (710 mg DA g-1 dry weight of fecal sample) is the highest reported in southern right whales to date. The current findings demonstrate for the first time that southern right whales, E. australis, are exposed to DA via copepods as vectors during their calving season in the gulfs of PV.
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southern right whale eubalaena australis calf mortality at peninsula valdes argentina are harmful algal blooms to blame
Marine Mammal Science, 2016Co-Authors: Cara Wilson, Victoria J Rowntree, Mónica Susana Hoffmeyer, Spencer E. Fire, Norma Santinelli, Soledad Díaz Ovejero, Viviana A Sastre, Valeria C DagostinoAbstract:Peninsula Valdes (PV) in Argentina is an important calving ground for southern right whales (SRWs, Eubalaena australis). Since 2005, right whale mortality has increased at PV, with most of the deaths (~90%) being calves <3 mo old. We investigated the potential involvement of harmful algal blooms (HABs) in these deaths by examining data that include: timing of the SRW deaths, biotoxins in samples from dead SRWs, abundances of the diatom, Pseudo-Nitzschia spp., and the dinoflagellate, Alexandrium tamarense, shellfish harvesting closure dates, seasonal availability of whale prey at PV and satellite chlorophyll data. Evidence of the whales' exposure to HAB toxins includes trace levels of paralytic shellfish toxins (PSTs) and domoic acid (DA) in tissues of some dead whales, and fragments of Pseudo-Nitzschia spp. frustules in whale feces. Additionally, whales are present at PV during both closures of the shellfish industry (due to high levels of PSTs) and periods with high levels of Pseudo-Nitzschia spp. and A. tamarense. There is a positive statistical relationship between monthly Pseudo-Nitzschia densities (but not A. tamarense) and calf deaths in both gulfs of PV.
José M. Franco - One of the best experts on this subject based on the ideXlab platform.
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preliminary study for rapid determination of phycotoxins in microalgae whole cells using matrix assisted laser desorption ionization time of flight mass spectrometry
Rapid Communications in Mass Spectrometry, 2011Co-Authors: Beatriz Paz, Pilar Riobó, José M. FrancoAbstract:Rapid and sensitive methods for identification of several phycotoxins produced by microalgae species such as yessotoxins (YTXs) for Protoceratium reticulatum, okadaic acid (OA) and pectenotoxins (PTXs) for Prorocentrum spp. and Dinophysis spp., Palytoxins (PLTXs) for Ostreopsis spp., ciguatoxins (CTXs) for Gambierdiscus spp. or domoic acid (DA) for Pseudo-Nitzschia spp. are of great importance to the shellfish and fish industry. In this study, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used to detect several phycotoxins in whole cells of some microalgae which are known as toxin producers. To achieve an appropriate MALDI matrix and a sample preparation method, several matrices and solvent mixtures were tested. The most appropriate matrix system for toxin detection was obtained with 10 µg μL–1 of DHB in 0.1% TFA/ACN (3:7, v/v) by mixing the intact cells with the matrix solution directly on the MALDI target (dried-droplet technique). Toxin detection by this procedure is much faster than current procedures based on solvent extraction and chromatographic separation. This method allowed the rapid detection of main phycotoxins in some dinoflagellate cells of genus Ostreopsis, Prorocentrum, Protoceratium, Gambierdiscus, Dinophysis and diatoms from Pseudo-Nitzschia genus. Copyright © 2011 John Wiley & Sons, Ltd.
Adrian Marchetti - One of the best experts on this subject based on the ideXlab platform.
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marine snow formation by the toxin producing diatom pseudo nitzschia australis
Harmful Algae, 2017Co-Authors: Astrid Schnetzer, Adrian Marchetti, Robert H Lampe, Claudia R Beniteznelson, Christopher L Osburn, Avery O TattersAbstract:Abstract The formation of marine snow (MS) by the toxic diatom Pseudo-nitschia australis was simulated using a roller table experiment. Concentrations of particulate and dissolved domoic acid (pDA and dDA) differed significantly among exponential phase and MS formation under simulated near surface conditions (16 °C/12:12-dark:light cycle) and also differed compared to subsequent particle decomposition at 4 °C in the dark, mimicking conditions in deeper waters. Particulate DA was first detected at the onset of exponential growth, reached maximum levels associated with MS aggregates (1.21 ± 0.24 ng mL−1) and declined at an average loss rate of ∼1.2% pDA day−1 during particle decomposition. Dissolved DA concentrations increased throughout the experiment and reached a maximum of ∼20 ng mL−1 at final sampling on day 88. The succession by P. australis from active growth to aggregation resulted in increasing MS toxicity and based on DA loading of particles and known in situ sinking speeds, a significant amount of toxin could have easily reached the deeper ocean or seafloor. MS formation was further associated with significant dDA accumulation at a ratio of pDA: dDA: cumulative dDA of approximately 1:10:100. Overall, this study confirms that MS functions as a major vector for toxin flux to depth, that Pseudo-Nitzschia-derived aggregates should be considered ‘toxic snow’ for MS-associated organisms, and that effects of MS toxicity on interactions with aggregate-associated microbes and zooplankton consumers warrant further consideration.
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Iron requirements of the pennate diatom Pseudo-Nitzschia: Comparison of oceanic (high-nitrate, low-chlorophyll waters) and coastal species
2014Co-Authors: Adrian Marchetti, Maria T Maldonado, Erin S. Lane, Paul J. HarrisonAbstract:We quantified and compared physiological parameters and iron requirements of several oceanic Pseudonitzschia spp., newly isolated from the high-nitrate, low-chlorophyll waters of the northeast subarctic Pacific, with coastal Pseudo-Nitzschia spp. and the oceanic centric diatom Thalassiosira oceanica at a range of iron concentrations. In iron-replete conditions, the iron (Fe) : carbon (C) ratios in the six Pseudo-Nitzschia isolates ranged from 157 mmol Fe mol C 21 to 248 mmol Fe mol C 21, with no apparent differences between oceanic and coastal isolates. In low iron conditions, all Pseudo-Nitzschia spp. exhibited marked reductions in photosynthetic efficiency, whereas the extent of the reductions in specific growth rates varied among species. When iron-limited, the Fe: C ratios decreased significantly in all oceanic Pseudo-Nitzschia species, with the lowest ratios ranging from 2.8 mmol Fe mol C 21 to 3.7 mmol Fe mol C 21. Combined with faster growth rates, lower Fe: C ratios in oceanic isolates of Pseudo-Nitzschia resulted in significantly higher iron-use efficiencies relative to their coastal congeners and T. oceanica. The wide range between iron-replete (Fe-Qhigh) and iron-limited (Fe-Qlow) quotas indicates that oceanic Pseudo-Nitzschia spp. have an extensive plasticity in iron contents relative to other diatoms grown at similar iron concentrations reported in the literature; the Fe-Qhigh: Fe-Qlow ratios for oceanic species were 46 to 67, whereas for coastal Pseudo-Nitzschia species they were 16 and 43. We suggest that the ability of oceani
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ferritin is used for iron storage in bloom forming marine pennate diatoms
Nature, 2009Co-Authors: Adrian Marchetti, Micaela S Parker, Michael E. P. Murphy, Lauren P Moccia, Angele L Arrieta, Francois Ribalet, Maria T Maldonado, Virginia E ArmbrustAbstract:The non-haem protein ferritin is used by many plants, animals and microorganisms to store iron in a non-toxic soluble form that can be readily mobilized when required. Ferritin has now been found in the two diatoms, Pseudo-Nitzschia and Fragilariopsis, that dominate phytoplankton blooms induced by both natural and artificial oceanic iron supplementation. This is the first report of ferritin in any member of the Stramenopila, the eukaryote lineage that includes many plankton components including unicellular algae, diatoms and macroalgae. Phylogenetic analysis suggests that ferritin arose in this small subset of diatoms via lateral gene transfer, and it may be key to their success in the 30–40% of ocean waters in which iron availability is the factor limiting primary productivity. Natural or artificial oceanic iron supplementation induces blooms that are dominated by pennate diatoms. It is shown that these diatoms contain the iron storage protein ferritin, which may explain their success in iron-limited waters. Primary productivity in 30–40% of the world’s oceans is limited by availability of the micronutrient iron1,2. Regions with chronically low iron concentrations are sporadically pulsed with new iron inputs by way of dust3 or lateral advection from continental margins4. Addition of iron to surface waters in these areas induces massive phytoplankton blooms dominated primarily by pennate diatoms5,6. Here we provide evidence that the bloom-forming pennate diatoms Pseudo-Nitzschia and Fragilariopsis use the iron-concentrating protein, ferritin, to safely store iron. Ferritin has not been reported previously in any member of the Stramenopiles, a diverse eukaryotic lineage that includes unicellular algae, macroalgae and plant parasites. Phylogenetic analyses suggest that ferritin may have arisen in this small subset of diatoms through a lateral gene transfer. The crystal structure and functional assays of recombinant ferritin derived from Pseudo-Nitzschia multiseries reveal a maxi-ferritin that exhibits ferroxidase activity and binds iron. The protein is predicted to be targeted to the chloroplast to control the distribution and storage of iron for proper functioning of the photosynthetic machinery. Abundance of Pseudo-Nitzschia ferritin transcripts is regulated by iron nutritional status, and is closely tied to the loss and recovery of photosynthetic competence. Enhanced iron storage with ferritin allows the oceanic diatom Pseudo-Nitzschia granii to undergo several more cell divisions in the absence of iron than the comparably sized, oceanic centric diatom Thalassiosira oceanica. Ferritin in pennate diatoms probably contributes to their success in chronically low-iron regions that receive intermittent iron inputs, and provides an explanation for the importance of these organisms in regulating oceanic CO2 over geological timescales7,8.
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Ferritin is used for iron storage in bloom-forming marine pennate diatoms
Nature, 2008Co-Authors: Adrian Marchetti, Micaela S Parker, Michael E. P. Murphy, Lauren P Moccia, Angele L Arrieta, Francois Ribalet, Maria T Maldonado, Ellen O. Lin, E. Virginia ArmbrustAbstract:The non-haem protein ferritin is used by many plants, animals and microorganisms to store iron in a non-toxic soluble form that can be readily mobilized when required. Ferritin has now been found in the two diatoms, Pseudo-Nitzschia and Fragilariopsis, that dominate phytoplankton blooms induced by both natural and artificial oceanic iron supplementation. This is the first report of ferritin in any member of the Stramenopila, the eukaryote lineage that includes many plankton components including unicellular algae, diatoms and macroalgae. Phylogenetic analysis suggests that ferritin arose in this small subset of diatoms via lateral gene transfer, and it may be key to their success in the 30–40% of ocean waters in which iron availability is the factor limiting primary productivity. Natural or artificial oceanic iron supplementation induces blooms that are dominated by pennate diatoms. It is shown that these diatoms contain the iron storage protein ferritin, which may explain their success in iron-limited waters. Primary productivity in 30–40% of the world’s oceans is limited by availability of the micronutrient iron1,2. Regions with chronically low iron concentrations are sporadically pulsed with new iron inputs by way of dust3 or lateral advection from continental margins4. Addition of iron to surface waters in these areas induces massive phytoplankton blooms dominated primarily by pennate diatoms5,6. Here we provide evidence that the bloom-forming pennate diatoms Pseudo-Nitzschia and Fragilariopsis use the iron-concentrating protein, ferritin, to safely store iron. Ferritin has not been reported previously in any member of the Stramenopiles, a diverse eukaryotic lineage that includes unicellular algae, macroalgae and plant parasites. Phylogenetic analyses suggest that ferritin may have arisen in this small subset of diatoms through a lateral gene transfer. The crystal structure and functional assays of recombinant ferritin derived from Pseudo-Nitzschia multiseries reveal a maxi-ferritin that exhibits ferroxidase activity and binds iron. The protein is predicted to be targeted to the chloroplast to control the distribution and storage of iron for proper functioning of the photosynthetic machinery. Abundance of Pseudo-Nitzschia ferritin transcripts is regulated by iron nutritional status, and is closely tied to the loss and recovery of photosynthetic competence. Enhanced iron storage with ferritin allows the oceanic diatom Pseudo-Nitzschia granii to undergo several more cell divisions in the absence of iron than the comparably sized, oceanic centric diatom Thalassiosira oceanica. Ferritin in pennate diatoms probably contributes to their success in chronically low-iron regions that receive intermittent iron inputs, and provides an explanation for the importance of these organisms in regulating oceanic CO2 over geological timescales7,8.
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coupled changes in the cell morphology and elemental c n and si composition of the pennate diatom pseudo nitzschia due to iron deficiency
Limnology and Oceanography, 2007Co-Authors: Adrian Marchetti, Paul HarrisonAbstract:We investigated the changes in cell morphology and elemental composition with varying iron nutritional status in four oceanic and two coastal isolates of the marine pennate diatom Pseudo-Nitzschia. When iron-deficient, most isolates exhibited slower specific growth rates (m), reduced maximum photochemical yields (WM), and lower chlorophyll a (Chl a) contents than iron-replete cultures. Iron-deficient cells exhibited reduced cell volumes, primarily as the result of decreased valve transapical widths, which increased the valve aspect ratios. The increase in aspect ratios varied among isolates and was not correlated with the degree of growth limitation due to irondeficiency. In all Pseudo-Nitzschia isolates, the mean carbon (Ccell), nitrogen (Ncell), and silicon (Sicell) cell quotas of iron-deficient cells decreased when compared to iron-replete cells. Similarly, in five out of the six isolates, the mean C and N quotas normalized per unit cell volume (Cvol and Nvol) of iron-deficient cells also decreased, but by a lesser extent. In contrast, there were no clear differences in the changes in the mean Si quotas normalized per unit cell surface area (Sisa). The Sicell :N cell and Sicell :C cell ratios (quotas normalized per cell) of iron-deficient cells increased compared to iron-replete conditions due to greater reductions in C and N cell quotas compared to Si cell quotas. This increase in the Sicell :N cell ratio was proportional to the changes in the valve aspect ratios. Our results show that iron-deficient Pseudo-Nitzschia cells acclimate to low iron concentrations by increasing their valve aspect ratios, thus reducing their cell volumes and increasing their surface area–to–volume (SA : V) ratios. These changes in cell morphology increase the Si-containing valve surface area relative to the volume of the internal components, which may then influence the cellular elemental composition, in particular, the Si : N and Si : C ratios.
