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Thomas Mock - One of the best experts on this subject based on the ideXlab platform.
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Diatom Molecular Research Comes of Age: Model Species for Studying Phytoplankton Biology and Diversity
The Plant cell, 2020Co-Authors: Angela Falciatore, Marianne Jaubert, Jean-pierre Bouly, Benjamin Bailleul, Thomas MockAbstract:Diatoms are the world's most diverse group of algae, comprising at least 100,000 species. Contributing ;20% of annual global carbon fixation, they underpin major aquatic food webs and drive global biogeochemical cycles. Over the past two decades, Thalassiosira pseudonana and Phaeodactylum tricornutum have become the most important model systems for diatom molecular research, ranging from cell biology to ecophysiology, due to their rapid growth rates, small genomes, and the cumulative wealth of associated genetic resources. To explore the evolutionary divergence of diatoms, additional model species are emerging, such as Fragilariopsis Cylindrus and Pseudo-nitzschia multistriata. Here, we describe how functional genomics and reverse genetics have contributed to our understanding of this important class of microalgae in the context of evolution, cell biology, and metabolic adaptations. Our review will also highlight promising areas of investigation into the diversity of these photosynthetic organisms, including the discovery of new molecular pathways governing the life of secondary plastid-bearing organisms in aquatic environments.
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diatom molecular research comes of age model species for studying phytoplankton biology and diversity
The Plant Cell, 2020Co-Authors: Marianne Jaubert, Angela Falciatore, Jean-pierre Bouly, Benjamin Bailleul, Thomas MockAbstract:Diatoms are the most diverse group of algae with at least 100,000 species. Contributing approximately 20% of annual global carbon fixation, they underpin major aquatic food webs and drive global biogeochemical cycles. Over the last two decades, Thalassiosira pseudonana and Phaeodactylum tricornutum have become the most important references for diatom molecular research, ranging from cell biology to ecophysiology, because of their rapid growth rates, small genomes and the cumulative wealth of associated genetic resources. To ascertain the significance of the evolutionary divergence of diatoms, additional references are emerging such as Fragilariopsis Cylindrus and Pseudo-nitzschia multistriata. Here, we describe how functional genomics and reverse genetics have contributed to our understanding of this important class of microalgae in the context of evolution, cell biology and metabolic adaptations. Our review will also highlight promising areas of investigation into the diversity of these photosynthetic organisms, including the discovery of new molecular pathways governing the life of secondary plastid-bearing organisms in aquatic environments.
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Identifying metabolic pathways for production of extracellular polymeric substances by the diatom Fragilariopsis Cylindrus inhabiting sea ice
The ISME Journal, 2018Co-Authors: Shazia N. Aslam, Jan Strauss, Thomas Mock, David N. Thomas, Graham J. C. UnderwoodAbstract:Diatoms are significant primary producers in sea ice, an ephemeral habitat with steep vertical gradients of temperature and salinity characterizing the ice matrix environment. To cope with the variable and challenging conditions, sea ice diatoms produce polysaccharide-rich extracellular polymeric substances (EPS) that play important roles in adhesion, cell protection, ligand binding and as organic carbon sources. Significant differences in EPS concentrations and chemical composition corresponding to temperature and salinity gradients were present in sea ice from the Weddell Sea and Eastern Antarctic regions of the Southern Ocean. To reconstruct the first metabolic pathway for EPS production in diatoms, we exposed Fragilariopsis Cylindrus , a key bi-polar diatom species, to simulated sea ice formation. Transcriptome profiling under varying conditions of EPS production identified a significant number of genes and divergent alleles. Their complex differential expression patterns under simulated sea ice formation was aligned with physiological and biochemical properties of the cells, and with field measurements of sea ice EPS characteristics. Thus, the molecular complexity of the EPS pathway suggests metabolic plasticity in F. Cylindrus is required to cope with the challenging conditions of the highly variable and extreme sea ice habitat.
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building a locally diploid genome and transcriptome of the diatom fragilariopsis Cylindrus
Scientific Data, 2017Co-Authors: Pirita Paajanen, Jan Strauss, Cock Van Oosterhout, Mark Mcmullan, Matthew D Clark, Thomas MockAbstract:The genome of the cold-adapted diatom Fragilariopsis Cylindrus is characterized by highly diverged haplotypes that intersperse its homozygous genome. Here, we describe how a combination of PacBio DNA and Illumina RNA sequencing can be used to resolve this complex genomic landscape locally into the highly diverged haplotypes, and how to map various environmentally controlled transcripts onto individual haplotypes. We assembled PacBio sequence data with the FALCON assembler and created a haplotype resolved annotation of the assembly using annotations of a Sanger sequenced F. Cylindrus genome. RNA-seq datasets from six different growth conditions were used to resolve allele-specifc gene expression in F. Cylindrus. This approach enables to study differential expression of alleles in a complex genomic landscape and provides a useful tool to study how diverged haplotypes in diploid organisms are used for adaptation and evolution to highly variable environments.
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Evolutionary genomics of the cold-adapted diatom Fragilariopsis Cylindrus.
Nature, 2017Co-Authors: Thomas Mock, Pirita Paajanen, Jan Strauss, Mark Mcmullan, Robert Otillar, Jeremy Schmutz, Asaf Salamov, Remo Sanges, Andrew Toseland, Ben J WardAbstract:The Southern Ocean houses a diverse and productive community of organisms. Unicellular eukaryotic diatoms are the main primary producers in this environment, where photosynthesis is limited by low concentrations of dissolved iron and large seasonal fluctuations in light, temperature and the extent of sea ice. How diatoms have adapted to this extreme environment is largely unknown. Here we present insights into the genome evolution of a cold-adapted diatom from the Southern Ocean, Fragilariopsis Cylindrus, based on a comparison with temperate diatoms. We find that approximately 24.7 per cent of the diploid F. Cylindrus genome consists of genetic loci with alleles that are highly divergent (15.1 megabases of the total genome size of 61.1 megabases). These divergent alleles were differentially expressed across environmental conditions, including darkness, low iron, freezing, elevated temperature and increased CO2. Alleles with the largest ratio of non-synonymous to synonymous nucleotide substitutions also show the most pronounced condition-dependent expression, suggesting a correlation between diversifying selection and allelic differentiation. Divergent alleles may be involved in adaptation to environmental fluctuations in the Southern Ocean.
Kevin R Arrigo - One of the best experts on this subject based on the ideXlab platform.
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the effect of iron limitation on the photophysiology of phaeocystis antarctica prymnesiophyceae and fragilariopsis Cylindrus bacillariophyceae under dynamic irradiance
Journal of Phycology, 2012Co-Authors: Annecarlijn Alderkamp, Matthew M Mills, Gert L Van Dijken, Gemma Kulk, Anita G J Buma, Ronald J W Visser, Kevin R ArrigoAbstract:The effects of iron limitation on photoacclimation to dynamic irradiance were studied in Phaeocystis antarctica G. Karst. and Fragilariopsis Cylindrus (Grunow) W. Krieg. in terms of growth rate, photosynthetic parameters, pigment composition, and fluorescence characteristics. Under dynamic light conditions mimicking vertical mixing below the euphotic zone, P. antarctica displayed higher growth rates than F. Cylindrus both under iron (Fe)-replete and Fe-limiting conditions. Both species showed xanthophyll de-epoxidation that was accompanied by low levels of nonphotochemical quenching (NPQ) during the irradiance maximum of the light cycle. The potential for NPQ at light levels corresponding to full sunlight was substantial in both species and increased under Fe limitation in F. Cylindrus. Although the decline in Fv /Fm under Fe limitation was similar in both species, the accompanying decrease in the maximum rate of photosynthesis and growth rate was much stronger in F. Cylindrus. Analysis of the electron transport rates through PSII and on to carbon (C) fixation revealed a large potential for photoprotective cyclic electron transport (CET) in F. Cylindrus, particularly under Fe limitation. Probably, CET aided the photoprotection in F. Cylindrus, but it also reduced photosynthetic efficiency at higher light intensities. P. antarctica, on the other hand, was able to efficiently use electrons flowing through PSII for C fixation at all light levels, particularly under Fe limitation. Thus, Fe limitation enhanced the photophysiological differences between P. antarctica and diatoms, supporting field observations where P. antarctica is found to dominate deeply mixed water columns, whereas diatoms dominate shallower mixed layers.
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strategies and rates of photoacclimation in two major southern ocean phytoplankton taxa phaeocystis antarctica haptophyta and fragilariopsis Cylindrus bacillariophyceae
Journal of Phycology, 2010Co-Authors: Lindsey R Kropuenske, Matthew M Mills, Gert L Van Dijken, Annecarlijn Alderkamp, Gry Mine Berg, Dale H Robinson, Nicholas A Welschmeyer, Kevin R ArrigoAbstract:We investigated rates and mechanisms of photoacclimation in cultures of Phaeocystis antarctica G. Karst. and Fragilariopsis Cylindrus (Grunow) Willi Krieg, phytoplankton taxa that each dominate distinct areas of the Ross Sea, Antarctica. Both P. antarctica and F. Cylindrus acclimated to increases in irradiance by reducing the effective size of the pigment antenna (σPSII) via xanthophyll-cycle activity and reductions in chl. While enhanced photoprotection facilitated increases in specific growth rate and eventually led to higher light-saturated photosynthetic rates (Pcellm) in P. antarctica, increases in those variables were much smaller in F. Cylindrus. In response to a lower irradiance, relaxation of xanthophyll-cycle activity led to an increase in σPSII in both taxa, which occurred much more slowly in F. Cylindrus. A surprising increase in specific growth rate over the first 36 h of acclimation in P. antarctica may have facilitated the significant reductions in Pcellm observed in that taxon. In general, P. antarctica acclimated more quickly to changes in irradiance than F. Cylindrus, exhibited a wider range in photosynthetic rates, but was more susceptible to photoinhibition. This acclimation strategy is consistent with growth in deeply mixed water columns with variations in irradiance that allow time for repair. In contrast, the slower acclimation rates, extensive photoprotection, and low photoinhibition exhibited by F. Cylindrus suggest that it does not require the same period for repair as P. antarctica and is best suited for growth in habitats with relatively uniform irradiance, such as shallow mixed layers or sea ice.
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photophysiology in two major southern ocean phytoplankton taxa photosynthesis and growth of phaeocystis antarctica and fragilariopsis Cylindrus under different irradiance levels
Integrative and Comparative Biology, 2010Co-Authors: Kevin R Arrigo, Lindsey R Kropuenske, Matthew M Mills, Gert L Van Dijken, Annecarlijn Alderkamp, Dale H RobinsonAbstract:Synopsis The Ross Sea, Antarctica, supports two distinct populations of phytoplankton, one that grows well in sea ice and blooms in the shallow mixed layers of the Western marginal ice zone and the other that can be found in sea ice but thrives in the deeply mixed layers of the Ross Sea. Dominated by diatoms (e.g. Fragilariopsis Cylindrus) and the prymnesiophyte Phaeocystis antarctica, respectively, the processes leading to the development of these different phytoplankton assemblages are not well known. The goal of this article was to gain a better understanding of the photophysiological characteristics that allow each taxon to dominate its specific habitat. Cultures of F. Cylindrus and P. antarctica were each grown semi-continuously at four different constant irradiances (5, 25, 65, and 125 � molquanta/m 2 /s). Fragilariopsis Cylindrus produced far less photosynthetic pigment per cell than did P. antarctica but much more photoprotective pigment. Fragilariopsis Cylindrus also exhibited substantially lower rates of photosynthesis and growth but also was far less susceptible to photoinhibition of cell growth. Excess photosynthetic capacity, a measure of the ability of phytoplankton to exploit variable light environments, was significantly higher in both strains of P. antarctica than in F. Cylindrus. The combination of these characteristics suggests that F. Cylindrus has a competitive advantage under conditions where mixed layers are shallow and light levels are relatively constant and high. In contrast, P. antarctica should dominate waters where mixed layers are deep and light levels are variable. These results are consistent with distributions of phytoplankton in the Ross Sea and suggest that light is the primary factor determining composition of phytoplankton communities.
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photophysiology in two southern ocean phytoplankton taxa photosynthesis of phaeocystis antarctica prymnesiophyceae and fragilariopsis Cylindrus bacillariophyceae under simulated mixed layer irradiance
Journal of Phycology, 2010Co-Authors: Matthew M Mills, Lindsey R Kropuenske, Gert L Van Dijken, Annecarlijn Alderkamp, Gry Mine Berg, Dale H Robinson, Nicholas A Welschmeyer, Kevin R ArrigoAbstract:In the Ross Sea, the prymnesiophyte Phaeocystis antarctica G. Karst. dominates deeply mixed water columns, while diatoms dominate shallower mixed layers. Understanding what controls the dynamics of these two phytoplankton taxa is essential because they dominate virtually all coastal polar waters, have different nutrient utilization characteristics, and support dissimilar food webs. We cultured two strains of P. antarctica and one strain of the diatom Fragilariopsis Cylindrus (Grunow) Willi Krieg under three dynamic irradiance regimes that simulated different mixed-layer depths and measured their photosynthetic characteristics, cellular pigment concentrations, and cellular carbon and nitrogen content. In both species, chl a–normalized maximum carbon uptake rate (Pm* ) and specific growth rate were highest in the deeply mixed treatment that had a dark period. In all irradiance treatments, both (Pm* ) and photosynthetic efficiency (α*) were greater for the two P. antarctica strains than for the F. Cylindrus strain. In contrast, P. antarctica strains were more susceptible to photoinhibition (β*) than the F. Cylindrus strain. When photosynthetic rates of each phytoplankton taxon were normalized by cellular particulate organic carbon (POC), the difference in the maximal photosynthetic rate () was generally reduced. In the dynamic irradiance treatment that simulated the shallowest mixed-layer irradiance, all three phytoplankton had similar ; however, the diatom had a 2-fold higher POC-normalized photosynthetic efficiency (αC). Finally, we performed calculations using the measured POC-normalized photosynthetic parameters to show that αC and can play a greater role than βC in determining the competitive outcome between P. antarctica and F. Cylindrus in both shallow and deep mixed-layer environments of the Ross Sea.
Jan Strauss - One of the best experts on this subject based on the ideXlab platform.
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Genome-Scale Metabolic Reconstruction and in Silico Perturbation Analysis of the Polar Diatom Fragilariopsis Cylindrus Predicts High Metabolic Robustness
Biology, 2020Co-Authors: Michel Lavoie, Jan Strauss, Blanche Saint-béat, Sébastien Guerin, Antoine Allard, Simon Hardy, Angela Falciatore, Johann LavaudAbstract:Diatoms are major primary producers in polar environments where they can actively grow under extremely variable conditions. Integrative modeling using a genome-scale model (GSM) is a powerful approach to decipher the complex interactions between components of diatom metabolism and can provide insights into metabolic mechanisms underlying their evolutionary success in polar ecosystems. We developed the first GSM for a polar diatom, Fragilariopsis Cylindrus, which enabled us to study its metabolic robustness using sensitivity analysis. We find that the predicted growth rate was robust to changes in all model parameters (i.e., cell biochemical composition) except the carbon uptake rate. Constraints on total cellular carbon buffer the effect of changes in the input parameters on reaction fluxes and growth rate. We also show that single reaction deletion of 20% to 32% of active (nonzero flux) reactions and single gene deletion of 44% to 55% of genes associated with active reactions affected the growth rate, as well as the production fluxes of total protein, lipid, carbohydrate, DNA, RNA, and pigments by less than 1%, which was due to the activation of compensatory reactions (e.g., analogous enzymes and alternative pathways) with more highly connected metabolites involved in the reactions that were robust to deletion. Interestingly, including highly divergent alleles unique for F. Cylindrus increased its metabolic robustness to cellular perturbations even more. Overall, our results underscore the high robustness of metabolism in F. Cylindrus, a feature that likely helps to maintain cell homeostasis under polar conditions.
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Identifying metabolic pathways for production of extracellular polymeric substances by the diatom Fragilariopsis Cylindrus inhabiting sea ice
The ISME Journal, 2018Co-Authors: Shazia N. Aslam, Jan Strauss, Thomas Mock, David N. Thomas, Graham J. C. UnderwoodAbstract:Diatoms are significant primary producers in sea ice, an ephemeral habitat with steep vertical gradients of temperature and salinity characterizing the ice matrix environment. To cope with the variable and challenging conditions, sea ice diatoms produce polysaccharide-rich extracellular polymeric substances (EPS) that play important roles in adhesion, cell protection, ligand binding and as organic carbon sources. Significant differences in EPS concentrations and chemical composition corresponding to temperature and salinity gradients were present in sea ice from the Weddell Sea and Eastern Antarctic regions of the Southern Ocean. To reconstruct the first metabolic pathway for EPS production in diatoms, we exposed Fragilariopsis Cylindrus , a key bi-polar diatom species, to simulated sea ice formation. Transcriptome profiling under varying conditions of EPS production identified a significant number of genes and divergent alleles. Their complex differential expression patterns under simulated sea ice formation was aligned with physiological and biochemical properties of the cells, and with field measurements of sea ice EPS characteristics. Thus, the molecular complexity of the EPS pathway suggests metabolic plasticity in F. Cylindrus is required to cope with the challenging conditions of the highly variable and extreme sea ice habitat.
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building a locally diploid genome and transcriptome of the diatom fragilariopsis Cylindrus
Scientific Data, 2017Co-Authors: Pirita Paajanen, Jan Strauss, Cock Van Oosterhout, Mark Mcmullan, Matthew D Clark, Thomas MockAbstract:The genome of the cold-adapted diatom Fragilariopsis Cylindrus is characterized by highly diverged haplotypes that intersperse its homozygous genome. Here, we describe how a combination of PacBio DNA and Illumina RNA sequencing can be used to resolve this complex genomic landscape locally into the highly diverged haplotypes, and how to map various environmentally controlled transcripts onto individual haplotypes. We assembled PacBio sequence data with the FALCON assembler and created a haplotype resolved annotation of the assembly using annotations of a Sanger sequenced F. Cylindrus genome. RNA-seq datasets from six different growth conditions were used to resolve allele-specifc gene expression in F. Cylindrus. This approach enables to study differential expression of alleles in a complex genomic landscape and provides a useful tool to study how diverged haplotypes in diploid organisms are used for adaptation and evolution to highly variable environments.
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Evolutionary genomics of the cold-adapted diatom Fragilariopsis Cylindrus.
Nature, 2017Co-Authors: Thomas Mock, Pirita Paajanen, Jan Strauss, Mark Mcmullan, Robert Otillar, Jeremy Schmutz, Asaf Salamov, Remo Sanges, Andrew Toseland, Ben J WardAbstract:The Southern Ocean houses a diverse and productive community of organisms. Unicellular eukaryotic diatoms are the main primary producers in this environment, where photosynthesis is limited by low concentrations of dissolved iron and large seasonal fluctuations in light, temperature and the extent of sea ice. How diatoms have adapted to this extreme environment is largely unknown. Here we present insights into the genome evolution of a cold-adapted diatom from the Southern Ocean, Fragilariopsis Cylindrus, based on a comparison with temperate diatoms. We find that approximately 24.7 per cent of the diploid F. Cylindrus genome consists of genetic loci with alleles that are highly divergent (15.1 megabases of the total genome size of 61.1 megabases). These divergent alleles were differentially expressed across environmental conditions, including darkness, low iron, freezing, elevated temperature and increased CO2. Alleles with the largest ratio of non-synonymous to synonymous nucleotide substitutions also show the most pronounced condition-dependent expression, suggesting a correlation between diversifying selection and allelic differentiation. Divergent alleles may be involved in adaptation to environmental fluctuations in the Southern Ocean.
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evolutionary genomics of the cold adapted diatom fragilariopsis Cylindrus
Nature, 2017Co-Authors: Thomas Mock, Pirita Paajanen, Jan Strauss, Mark Mcmullan, Robert Otillar, Jeremy Schmutz, Asaf Salamov, Remo SangesAbstract:The genome of the Southern Ocean phytoplankton Fragilariopsis Cylindrus differs markedly from the genomes of its more temperate relatives, with divergent alleles being differentially expressed in environmentally specific conditions such as freezing and darkness. Diatoms are the main primary producers in the Southern Ocean, but how they have adapted to an environment with such extremes of light and temperature has remained unknown. Here Thomas Mock et al. report the genome sequence of a cold-adapted diatom from the Southern Ocean, Fragilariopsis Cylindrus, and compare this 'psychrophile' with diatoms that evolved in temperate oceans. They find that its genome contains highly diverged alleles that are differentially expressed across environmental conditions. The Southern Ocean houses a diverse and productive community of organisms1,2. Unicellular eukaryotic diatoms are the main primary producers in this environment, where photosynthesis is limited by low concentrations of dissolved iron and large seasonal fluctuations in light, temperature and the extent of sea ice3,4,5,6,7. How diatoms have adapted to this extreme environment is largely unknown. Here we present insights into the genome evolution of a cold-adapted diatom from the Southern Ocean, Fragilariopsis Cylindrus8,9, based on a comparison with temperate diatoms. We find that approximately 24.7 per cent of the diploid F. Cylindrus genome consists of genetic loci with alleles that are highly divergent (15.1 megabases of the total genome size of 61.1 megabases). These divergent alleles were differentially expressed across environmental conditions, including darkness, low iron, freezing, elevated temperature and increased CO2. Alleles with the largest ratio of non-synonymous to synonymous nucleotide substitutions also show the most pronounced condition-dependent expression, suggesting a correlation between diversifying selection and allelic differentiation. Divergent alleles may be involved in adaptation to environmental fluctuations in the Southern Ocean.
Dale H Robinson - One of the best experts on this subject based on the ideXlab platform.
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strategies and rates of photoacclimation in two major southern ocean phytoplankton taxa phaeocystis antarctica haptophyta and fragilariopsis Cylindrus bacillariophyceae
Journal of Phycology, 2010Co-Authors: Lindsey R Kropuenske, Matthew M Mills, Gert L Van Dijken, Annecarlijn Alderkamp, Gry Mine Berg, Dale H Robinson, Nicholas A Welschmeyer, Kevin R ArrigoAbstract:We investigated rates and mechanisms of photoacclimation in cultures of Phaeocystis antarctica G. Karst. and Fragilariopsis Cylindrus (Grunow) Willi Krieg, phytoplankton taxa that each dominate distinct areas of the Ross Sea, Antarctica. Both P. antarctica and F. Cylindrus acclimated to increases in irradiance by reducing the effective size of the pigment antenna (σPSII) via xanthophyll-cycle activity and reductions in chl. While enhanced photoprotection facilitated increases in specific growth rate and eventually led to higher light-saturated photosynthetic rates (Pcellm) in P. antarctica, increases in those variables were much smaller in F. Cylindrus. In response to a lower irradiance, relaxation of xanthophyll-cycle activity led to an increase in σPSII in both taxa, which occurred much more slowly in F. Cylindrus. A surprising increase in specific growth rate over the first 36 h of acclimation in P. antarctica may have facilitated the significant reductions in Pcellm observed in that taxon. In general, P. antarctica acclimated more quickly to changes in irradiance than F. Cylindrus, exhibited a wider range in photosynthetic rates, but was more susceptible to photoinhibition. This acclimation strategy is consistent with growth in deeply mixed water columns with variations in irradiance that allow time for repair. In contrast, the slower acclimation rates, extensive photoprotection, and low photoinhibition exhibited by F. Cylindrus suggest that it does not require the same period for repair as P. antarctica and is best suited for growth in habitats with relatively uniform irradiance, such as shallow mixed layers or sea ice.
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photophysiology in two major southern ocean phytoplankton taxa photosynthesis and growth of phaeocystis antarctica and fragilariopsis Cylindrus under different irradiance levels
Integrative and Comparative Biology, 2010Co-Authors: Kevin R Arrigo, Lindsey R Kropuenske, Matthew M Mills, Gert L Van Dijken, Annecarlijn Alderkamp, Dale H RobinsonAbstract:Synopsis The Ross Sea, Antarctica, supports two distinct populations of phytoplankton, one that grows well in sea ice and blooms in the shallow mixed layers of the Western marginal ice zone and the other that can be found in sea ice but thrives in the deeply mixed layers of the Ross Sea. Dominated by diatoms (e.g. Fragilariopsis Cylindrus) and the prymnesiophyte Phaeocystis antarctica, respectively, the processes leading to the development of these different phytoplankton assemblages are not well known. The goal of this article was to gain a better understanding of the photophysiological characteristics that allow each taxon to dominate its specific habitat. Cultures of F. Cylindrus and P. antarctica were each grown semi-continuously at four different constant irradiances (5, 25, 65, and 125 � molquanta/m 2 /s). Fragilariopsis Cylindrus produced far less photosynthetic pigment per cell than did P. antarctica but much more photoprotective pigment. Fragilariopsis Cylindrus also exhibited substantially lower rates of photosynthesis and growth but also was far less susceptible to photoinhibition of cell growth. Excess photosynthetic capacity, a measure of the ability of phytoplankton to exploit variable light environments, was significantly higher in both strains of P. antarctica than in F. Cylindrus. The combination of these characteristics suggests that F. Cylindrus has a competitive advantage under conditions where mixed layers are shallow and light levels are relatively constant and high. In contrast, P. antarctica should dominate waters where mixed layers are deep and light levels are variable. These results are consistent with distributions of phytoplankton in the Ross Sea and suggest that light is the primary factor determining composition of phytoplankton communities.
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photophysiology in two southern ocean phytoplankton taxa photosynthesis of phaeocystis antarctica prymnesiophyceae and fragilariopsis Cylindrus bacillariophyceae under simulated mixed layer irradiance
Journal of Phycology, 2010Co-Authors: Matthew M Mills, Lindsey R Kropuenske, Gert L Van Dijken, Annecarlijn Alderkamp, Gry Mine Berg, Dale H Robinson, Nicholas A Welschmeyer, Kevin R ArrigoAbstract:In the Ross Sea, the prymnesiophyte Phaeocystis antarctica G. Karst. dominates deeply mixed water columns, while diatoms dominate shallower mixed layers. Understanding what controls the dynamics of these two phytoplankton taxa is essential because they dominate virtually all coastal polar waters, have different nutrient utilization characteristics, and support dissimilar food webs. We cultured two strains of P. antarctica and one strain of the diatom Fragilariopsis Cylindrus (Grunow) Willi Krieg under three dynamic irradiance regimes that simulated different mixed-layer depths and measured their photosynthetic characteristics, cellular pigment concentrations, and cellular carbon and nitrogen content. In both species, chl a–normalized maximum carbon uptake rate (Pm* ) and specific growth rate were highest in the deeply mixed treatment that had a dark period. In all irradiance treatments, both (Pm* ) and photosynthetic efficiency (α*) were greater for the two P. antarctica strains than for the F. Cylindrus strain. In contrast, P. antarctica strains were more susceptible to photoinhibition (β*) than the F. Cylindrus strain. When photosynthetic rates of each phytoplankton taxon were normalized by cellular particulate organic carbon (POC), the difference in the maximal photosynthetic rate () was generally reduced. In the dynamic irradiance treatment that simulated the shallowest mixed-layer irradiance, all three phytoplankton had similar ; however, the diatom had a 2-fold higher POC-normalized photosynthetic efficiency (αC). Finally, we performed calculations using the measured POC-normalized photosynthetic parameters to show that αC and can play a greater role than βC in determining the competitive outcome between P. antarctica and F. Cylindrus in both shallow and deep mixed-layer environments of the Ross Sea.
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photophysiology in two major southern ocean phytoplankton taxa photoprotection in phaeocystis antarctica and fragilariopsis Cylindrus
Limnology and Oceanography, 2009Co-Authors: Lindsey R Kropuenske, Matthew M Mills, Dale H Robinson, Nicholas A Welschmeyer, Gert L Van Dijken, Shaun Bailey, Kevin R ArrigoaAbstract:Phytoplankton communities in the Ross Sea, Antarctica, are characterized by the haptophyte Phaeocystis antarctica Karsten, which dominates deep mixed layers, and diatoms, including Fragilariopsis Cylindrus Grunow, that thrive in shallower mixed layers. To investigate whether differences in photoprotective strategies explain these distributions, photosynthetic parameters, pigments, and fluorescence properties were measured in cultures grown under several irradiance regimes and during acclimation to increased irradiance. In P. antarctica, cellular concentrations of all pigments declined with increasing growth irradiance under continuous light, but xanthophyll cycle pigment concentrations increased with increasing irradiance under dynamic conditions without changes in chlorophyll. In contrast, F. Cylindrus exhibited declines in chlorophyll cell−1 with increasing irradiance under both continuous and dynamic conditions, but xanthophyll cycle cell21 pigments increased under continuous irradiance and declined under dynamic irradiance. P. antarctica did not exhibit non-photochemical quenching (NPQ) unless exposed to irradiance in excess of the mean growth irradiance. F. Cylindrus exhibited NPQ in response to lower irradiances but displayed less photoinhibitory quenching than P. antarctica after exposure to very high irradiance. Inhibitor experiments suggest that both taxa rely upon xanthophyll cycle photoprotection to maintain photosynthetic performance but only P. antarctica relies heavily upon protein synthesis, presumably for D1 protein repair. F. Cylindrus can thrive in shallow mixed layers because its high capacity for heat dissipation minimizes photoinhibition. P. antarctica utilizes xanthophyll cycle photoprotection to a lesser degree, but is able to dominate deeper mixed layers by effectively repairing the photodamage incurred when it is mixed to the surface.
Matthew M Mills - One of the best experts on this subject based on the ideXlab platform.
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the effect of iron limitation on the photophysiology of phaeocystis antarctica prymnesiophyceae and fragilariopsis Cylindrus bacillariophyceae under dynamic irradiance
Journal of Phycology, 2012Co-Authors: Annecarlijn Alderkamp, Matthew M Mills, Gert L Van Dijken, Gemma Kulk, Anita G J Buma, Ronald J W Visser, Kevin R ArrigoAbstract:The effects of iron limitation on photoacclimation to dynamic irradiance were studied in Phaeocystis antarctica G. Karst. and Fragilariopsis Cylindrus (Grunow) W. Krieg. in terms of growth rate, photosynthetic parameters, pigment composition, and fluorescence characteristics. Under dynamic light conditions mimicking vertical mixing below the euphotic zone, P. antarctica displayed higher growth rates than F. Cylindrus both under iron (Fe)-replete and Fe-limiting conditions. Both species showed xanthophyll de-epoxidation that was accompanied by low levels of nonphotochemical quenching (NPQ) during the irradiance maximum of the light cycle. The potential for NPQ at light levels corresponding to full sunlight was substantial in both species and increased under Fe limitation in F. Cylindrus. Although the decline in Fv /Fm under Fe limitation was similar in both species, the accompanying decrease in the maximum rate of photosynthesis and growth rate was much stronger in F. Cylindrus. Analysis of the electron transport rates through PSII and on to carbon (C) fixation revealed a large potential for photoprotective cyclic electron transport (CET) in F. Cylindrus, particularly under Fe limitation. Probably, CET aided the photoprotection in F. Cylindrus, but it also reduced photosynthetic efficiency at higher light intensities. P. antarctica, on the other hand, was able to efficiently use electrons flowing through PSII for C fixation at all light levels, particularly under Fe limitation. Thus, Fe limitation enhanced the photophysiological differences between P. antarctica and diatoms, supporting field observations where P. antarctica is found to dominate deeply mixed water columns, whereas diatoms dominate shallower mixed layers.
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strategies and rates of photoacclimation in two major southern ocean phytoplankton taxa phaeocystis antarctica haptophyta and fragilariopsis Cylindrus bacillariophyceae
Journal of Phycology, 2010Co-Authors: Lindsey R Kropuenske, Matthew M Mills, Gert L Van Dijken, Annecarlijn Alderkamp, Gry Mine Berg, Dale H Robinson, Nicholas A Welschmeyer, Kevin R ArrigoAbstract:We investigated rates and mechanisms of photoacclimation in cultures of Phaeocystis antarctica G. Karst. and Fragilariopsis Cylindrus (Grunow) Willi Krieg, phytoplankton taxa that each dominate distinct areas of the Ross Sea, Antarctica. Both P. antarctica and F. Cylindrus acclimated to increases in irradiance by reducing the effective size of the pigment antenna (σPSII) via xanthophyll-cycle activity and reductions in chl. While enhanced photoprotection facilitated increases in specific growth rate and eventually led to higher light-saturated photosynthetic rates (Pcellm) in P. antarctica, increases in those variables were much smaller in F. Cylindrus. In response to a lower irradiance, relaxation of xanthophyll-cycle activity led to an increase in σPSII in both taxa, which occurred much more slowly in F. Cylindrus. A surprising increase in specific growth rate over the first 36 h of acclimation in P. antarctica may have facilitated the significant reductions in Pcellm observed in that taxon. In general, P. antarctica acclimated more quickly to changes in irradiance than F. Cylindrus, exhibited a wider range in photosynthetic rates, but was more susceptible to photoinhibition. This acclimation strategy is consistent with growth in deeply mixed water columns with variations in irradiance that allow time for repair. In contrast, the slower acclimation rates, extensive photoprotection, and low photoinhibition exhibited by F. Cylindrus suggest that it does not require the same period for repair as P. antarctica and is best suited for growth in habitats with relatively uniform irradiance, such as shallow mixed layers or sea ice.
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photophysiology in two major southern ocean phytoplankton taxa photosynthesis and growth of phaeocystis antarctica and fragilariopsis Cylindrus under different irradiance levels
Integrative and Comparative Biology, 2010Co-Authors: Kevin R Arrigo, Lindsey R Kropuenske, Matthew M Mills, Gert L Van Dijken, Annecarlijn Alderkamp, Dale H RobinsonAbstract:Synopsis The Ross Sea, Antarctica, supports two distinct populations of phytoplankton, one that grows well in sea ice and blooms in the shallow mixed layers of the Western marginal ice zone and the other that can be found in sea ice but thrives in the deeply mixed layers of the Ross Sea. Dominated by diatoms (e.g. Fragilariopsis Cylindrus) and the prymnesiophyte Phaeocystis antarctica, respectively, the processes leading to the development of these different phytoplankton assemblages are not well known. The goal of this article was to gain a better understanding of the photophysiological characteristics that allow each taxon to dominate its specific habitat. Cultures of F. Cylindrus and P. antarctica were each grown semi-continuously at four different constant irradiances (5, 25, 65, and 125 � molquanta/m 2 /s). Fragilariopsis Cylindrus produced far less photosynthetic pigment per cell than did P. antarctica but much more photoprotective pigment. Fragilariopsis Cylindrus also exhibited substantially lower rates of photosynthesis and growth but also was far less susceptible to photoinhibition of cell growth. Excess photosynthetic capacity, a measure of the ability of phytoplankton to exploit variable light environments, was significantly higher in both strains of P. antarctica than in F. Cylindrus. The combination of these characteristics suggests that F. Cylindrus has a competitive advantage under conditions where mixed layers are shallow and light levels are relatively constant and high. In contrast, P. antarctica should dominate waters where mixed layers are deep and light levels are variable. These results are consistent with distributions of phytoplankton in the Ross Sea and suggest that light is the primary factor determining composition of phytoplankton communities.
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photophysiology in two southern ocean phytoplankton taxa photosynthesis of phaeocystis antarctica prymnesiophyceae and fragilariopsis Cylindrus bacillariophyceae under simulated mixed layer irradiance
Journal of Phycology, 2010Co-Authors: Matthew M Mills, Lindsey R Kropuenske, Gert L Van Dijken, Annecarlijn Alderkamp, Gry Mine Berg, Dale H Robinson, Nicholas A Welschmeyer, Kevin R ArrigoAbstract:In the Ross Sea, the prymnesiophyte Phaeocystis antarctica G. Karst. dominates deeply mixed water columns, while diatoms dominate shallower mixed layers. Understanding what controls the dynamics of these two phytoplankton taxa is essential because they dominate virtually all coastal polar waters, have different nutrient utilization characteristics, and support dissimilar food webs. We cultured two strains of P. antarctica and one strain of the diatom Fragilariopsis Cylindrus (Grunow) Willi Krieg under three dynamic irradiance regimes that simulated different mixed-layer depths and measured their photosynthetic characteristics, cellular pigment concentrations, and cellular carbon and nitrogen content. In both species, chl a–normalized maximum carbon uptake rate (Pm* ) and specific growth rate were highest in the deeply mixed treatment that had a dark period. In all irradiance treatments, both (Pm* ) and photosynthetic efficiency (α*) were greater for the two P. antarctica strains than for the F. Cylindrus strain. In contrast, P. antarctica strains were more susceptible to photoinhibition (β*) than the F. Cylindrus strain. When photosynthetic rates of each phytoplankton taxon were normalized by cellular particulate organic carbon (POC), the difference in the maximal photosynthetic rate () was generally reduced. In the dynamic irradiance treatment that simulated the shallowest mixed-layer irradiance, all three phytoplankton had similar ; however, the diatom had a 2-fold higher POC-normalized photosynthetic efficiency (αC). Finally, we performed calculations using the measured POC-normalized photosynthetic parameters to show that αC and can play a greater role than βC in determining the competitive outcome between P. antarctica and F. Cylindrus in both shallow and deep mixed-layer environments of the Ross Sea.
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photophysiology in two major southern ocean phytoplankton taxa photoprotection in phaeocystis antarctica and fragilariopsis Cylindrus
Limnology and Oceanography, 2009Co-Authors: Lindsey R Kropuenske, Matthew M Mills, Dale H Robinson, Nicholas A Welschmeyer, Gert L Van Dijken, Shaun Bailey, Kevin R ArrigoaAbstract:Phytoplankton communities in the Ross Sea, Antarctica, are characterized by the haptophyte Phaeocystis antarctica Karsten, which dominates deep mixed layers, and diatoms, including Fragilariopsis Cylindrus Grunow, that thrive in shallower mixed layers. To investigate whether differences in photoprotective strategies explain these distributions, photosynthetic parameters, pigments, and fluorescence properties were measured in cultures grown under several irradiance regimes and during acclimation to increased irradiance. In P. antarctica, cellular concentrations of all pigments declined with increasing growth irradiance under continuous light, but xanthophyll cycle pigment concentrations increased with increasing irradiance under dynamic conditions without changes in chlorophyll. In contrast, F. Cylindrus exhibited declines in chlorophyll cell−1 with increasing irradiance under both continuous and dynamic conditions, but xanthophyll cycle cell21 pigments increased under continuous irradiance and declined under dynamic irradiance. P. antarctica did not exhibit non-photochemical quenching (NPQ) unless exposed to irradiance in excess of the mean growth irradiance. F. Cylindrus exhibited NPQ in response to lower irradiances but displayed less photoinhibitory quenching than P. antarctica after exposure to very high irradiance. Inhibitor experiments suggest that both taxa rely upon xanthophyll cycle photoprotection to maintain photosynthetic performance but only P. antarctica relies heavily upon protein synthesis, presumably for D1 protein repair. F. Cylindrus can thrive in shallow mixed layers because its high capacity for heat dissipation minimizes photoinhibition. P. antarctica utilizes xanthophyll cycle photoprotection to a lesser degree, but is able to dominate deeper mixed layers by effectively repairing the photodamage incurred when it is mixed to the surface.
