Studies on the long-term responses of marine phytoplankton to ongoing ocean acidification (OA) ar... more Studies on the long-term responses of marine phytoplankton to ongoing ocean acidification (OA) are appearing rapidly in the literature. However, only a few of these have investigated diatoms, which is disproportionate to their contribution to global primary production. Here we show that a population of the model diatom Phaeodactylum tricornutum, after growing under elevated CO (1000 μatm, HCL, pH : 7.70) for 1860 generations, showed significant differences in photosynthesis and growth from a population maintained in ambient CO and then transferred to elevated CO for 20 generations (HC). The HCL population had lower mitochondrial respiration, than did the control population maintained in ambient CO (400 μatm, LCL, pH : 8.02) for 1860 generations. Although the cells had higher respiratory carbon loss within 20 generations under the elevated CO , being consistent to previous findings, they downregulated their respiration to sustain their growth in longer duration under the OA condition...
Permeable sediments are common across continental shelves and are critical contributors to marine... more Permeable sediments are common across continental shelves and are critical contributors to marine biogeochemical cycling. Organic matter in permeable sediments is dominated by microalgae, which as eukaryotes have different anaerobic metabolic pathways to prokaryotes such as bacteria and archaea. Here we present analyses of flow-through reactor experiments showing that dissolved inorganic carbon is produced predominantly as a result of anaerobic eukaryotic metabolic activity. In our experiments, anaerobic production of dissolved inorganic carbon was consistently accompanied by large dissolved H2 production rates, suggesting the presence of fermentation. The production of both dissolved inorganic carbon and H2 persisted following administration of broad spectrum bactericidal antibiotics, but ceased following treatment with metronidazole. Metronidazole inhibits the ferredoxin/hydrogenase pathway of fermentative eukaryotic H2 production, suggesting that pathway as the source of H2 and d...
Increasing atmospheric CO2 concentrations are causing ocean acidification (OA), altering carbonat... more Increasing atmospheric CO2 concentrations are causing ocean acidification (OA), altering carbonate chemistry with consequences for marine organisms. Here we show that OA increases by 46-212% the production of phenolic compounds in phytoplankton grown under the elevated CO2 concentrations projected for the end of this century, compared with the ambient CO2 level. At the same time, mitochondrial respiration rate is enhanced under elevated CO2 concentrations by 130-160% in a single species or mixed phytoplankton assemblage. When fed with phytoplankton cells grown under OA, zooplankton assemblages have significantly higher phenolic compound content, by about 28-48%. The functional consequences of the increased accumulation of toxic phenolic compounds in primary and secondary producers have the potential to have profound consequences for marine ecosystem and seafood quality, with the possibility that fishery industries could be influenced as a result of progressive ocean changes.
Diatoms, an important group of phytoplankton, bloom annually in the Southern Ocean, covering thou... more Diatoms, an important group of phytoplankton, bloom annually in the Southern Ocean, covering thousands of square kilometers and dominating the region's phytoplankton communities. In their role as the major food source to marine grazers, diatoms supply carbon, nutrients and energy to the Southern Ocean food web. Prevailing environmental conditions influence diatom phenotypic traits (for example, photophysiology, macromolecular composition and morphology), which in turn affect the transfer of energy, carbon and nutrients to grazers and higher trophic levels, as well as oceanic biogeochemical cycles. The paucity of phenotypic data on Southern Ocean phytoplankton limits our understanding of the ecosystem and how it may respond to future environmental change. Here we used a novel approach to create a 'snapshot' of cell phenotype. Using mass spectrometry, we measured nitrogen (a proxy for protein), total carbon and carbon-13 enrichment (carbon productivity), then used this dat...
Microalgae are capable of acclimating to changes in light and ultraviolet radiation (UVR, 280-400... more Microalgae are capable of acclimating to changes in light and ultraviolet radiation (UVR, 280-400 nm). However, little is known about how the ecologically important coccolithophore Emiliania huxleyi responds to UVR when acclimated to different light regimes. Here, we grew E. huxleyi under indoor constant light or fluctuating sunlight with or without UVR, and investigated its growth, photosynthetic performance and pigmentation. Under the indoor constant light regime, the specific growth rate (μ) was highest, while fluctuating outdoor solar radiation significantly decreased the growth rate. Addition of UVR further decreased the growth rate. The repair rate of photosystem II (PSII), as reflected in changes in PSII quantum yield, showed an inverse correlation with growth rate. Cells grown under the indoor constant light regime exhibited the lowest repair rate, while cells from the outdoor fluctuating light regimes significantly increased their repair rate. Addition of UVR increased both...
The fate of diazotrophic nitrogen (N(D)) fixed by planktonic cyanobacteria in pelagic food webs r... more The fate of diazotrophic nitrogen (N(D)) fixed by planktonic cyanobacteria in pelagic food webs remains unresolved, particularly for toxic cyanophytes that are selectively avoided by most herbivorous zooplankton. Current theory suggests that N(D) fixed during cyanobacterial blooms can enter planktonic food webs contemporaneously with peak bloom biomass via direct grazing of zooplankton on cyanobacteria or via the uptake of bioavailable N(D) (exuded from viable cyanobacterial cells) by palatable phytoplankton or microbial consortia. Alternatively, N(D) can enter planktonic food webs post-bloom following the remineralization of bloom detritus. Although the relative contribution of these processes to planktonic nutrient cycles is unknown, we hypothesized that assimilation of bioavailable N(D) (e.g., nitrate, ammonium) by palatable phytoplankton and subsequent grazing by zooplankton (either during or after the cyanobacterial bloom) would be the primary pathway by which N(D) was incorpor...
Hypersaline environments pose a number of ecological and metabolic challenges to the organisms th... more Hypersaline environments pose a number of ecological and metabolic challenges to the organisms that live in them. Primary producers, such as halotolerant species of the green microalgal genus Dunaliella, are no exception. In this paper we focus on the problems posed to the acquisition and metabolism of inorganic nutrients and on the consequences of exposure to high light and UV radiation. We show that not only does growth in high salinity environments have repercussions on the flow of carbon into osmolytes such as glycerol, it also affects speciation of inorganic carbon and the uptake of inorganic ions by the cells. The strategies that Dunaliella adopt to optimize resource utilization and the interactions among metabolic pathways are also discussed.
The chlorophyte alga Dunaliella rerriolecra was exposed to UV-B radiation (UVBR) and the characte... more The chlorophyte alga Dunaliella rerriolecra was exposed to UV-B radiation (UVBR) and the characteristics of dissolved inorganic carbon (D1C)-dependent oxygen evolution, carbon fixation and CO2-concentrating mechanism (CCM) activity were examined. Exposure response measurements were ...
... Karen Kevekordes 1 , Daryl Holland 1 , Norbert HÄubner 1 , Sommer Jenkins 1 , Rebecca Koss 1 ... more ... Karen Kevekordes 1 , Daryl Holland 1 , Norbert HÄubner 1 , Sommer Jenkins 1 , Rebecca Koss 1 , Simon Roberts 1 , John A. Raven 2 , Charles M. Scrimgeour 3 , Kirsten Shelly 1 ... Badger, MR , JT Andrews , SM Whitney , M. Ludwig , DC Yellowlees , W. Leggat , and GD Price . ...
Most of the algae and cyanobacteria that have been critically examined express a carbon-concentra... more Most of the algae and cyanobacteria that have been critically examined express a carbon-concentrating mechanism (CCM) when grown at, or below, the current atmospheric CO 2 concentration. This paper considers algae that appear to lack a CCM. Critical examination of the evidence on which the presence or absence of a CCM is decided shows that more information is frequently needed before the criteria can be fully applied. Examples are the pathways of glycolate metabolism in nongreen algae, and the 13 C/ 12 C discrimination shown by form ID Rubisco in vitro. The available evidence suggests that the algae lacking CCMs are some terrestrial green microalgae, some florideophyte freshwater red macroalgae, and a number of florideophyte red macroalgae from the supralittoral, littoral, and sublittoral, and almost all of the freshwater chrysophytes and synurophytes examined. Certain environmental, biochemical , and biophysical factors may permit the occurrence of algae lacking CCMs. The absence of CCMs is presumably the plesiomorphic (i.e., ancestral) condition in cyanobacteria (and algae?). Résumé : La plupart des algues et des cyanobactéries, qui ont été examinées attentivement, possèdent un mécanisme de concentration du carbone (CCM), lorsqu'elles sont cultivées à des concentrations de CO 2 égales ou inférieures à celle de l'atmosphère. Les auteurs examinent ici les algues qui n'ont pas de CCM. Un examen critique des preuves sur lesquelles la présence ou l'absence d'un CCM est reconnue, montre qu'il faut souvent plus d'informations avant que le critère puisse être appliqué. Par exemple, on note les sentiers métaboliques du glycolate chez les algues nonvertes, et la discrimination des 13 C/ 12 C manifestée par la forme ID de la Rubisco. Les preuves actuelles suggèrent que les algues qui n'ont pas de CCM sont certaines microalgues vertes terrestres, certaines macro-algues rouges floridéophytes d'eau douce, et un nombre de macroalgues rouges floridéophytes du supralittoral, du littoral et du sublittoral, ainsi que la plupart des chrysophytes et des synurophytes d'eau douce examinées. Certains facteurs environnementaux, biochimiques et biophysiques peuvent permettre la présence d'algues dépourvues de CCM. L'absence de CCM constitue vraisembla-blement la condition plésiomorphe (c.-à-d. ancestrale), chez les cyanobactéries.
This chapter discusses two of the processes, namely photorespiration and chlororespiration, in al... more This chapter discusses two of the processes, namely photorespiration and chlororespiration, in algae that run counter to the oxygen-yielding reactions of photosynthesis and which involve the oxidation of carbohydrate and/or the consumption of oxygen. Photorespiration is associated with the oxygenase activity of Rubisco and the mechanisms by which cells recoup carbon and energy that would otherwise be lost from the
Phytoplankton life forms, including unicells, colonies, pseudocolonies, and multicellular organis... more Phytoplankton life forms, including unicells, colonies, pseudocolonies, and multicellular organisms, span a huge size range. The smallest unicells are less than 1 microm3 (e.g. cyanobacteria), while large unicellular diatoms may attain 10(9) microm3, being visible to the naked eye. Phytoplankton includes chemo-organotrophic unicells, colonies and multicellular organisms that depend on symbionts or kleptoplastids for their capacity to photosynthesize. Analyses of physical (transport within cells, diffusion boundary layers, package effect, turgor, and vertical movements) and biotic (grazing, viruses and other parasitoids) factors indicate potential ecological constraints and opportunities that differ among the life forms. There are also variations among life forms in elemental stoichiometry and in allometric relations between biovolume and specific growth. While many of these factors probably have ecological and evolutionary significance, work is needed to establish those that are most important, warranting explicit description in models. Other factors setting limitations on growth rate (selecting slow-growing species) await elucidation.
Studies on the long-term responses of marine phytoplankton to ongoing ocean acidification (OA) ar... more Studies on the long-term responses of marine phytoplankton to ongoing ocean acidification (OA) are appearing rapidly in the literature. However, only a few of these have investigated diatoms, which is disproportionate to their contribution to global primary production. Here we show that a population of the model diatom Phaeodactylum tricornutum, after growing under elevated CO (1000 μatm, HCL, pH : 7.70) for 1860 generations, showed significant differences in photosynthesis and growth from a population maintained in ambient CO and then transferred to elevated CO for 20 generations (HC). The HCL population had lower mitochondrial respiration, than did the control population maintained in ambient CO (400 μatm, LCL, pH : 8.02) for 1860 generations. Although the cells had higher respiratory carbon loss within 20 generations under the elevated CO , being consistent to previous findings, they downregulated their respiration to sustain their growth in longer duration under the OA condition...
Permeable sediments are common across continental shelves and are critical contributors to marine... more Permeable sediments are common across continental shelves and are critical contributors to marine biogeochemical cycling. Organic matter in permeable sediments is dominated by microalgae, which as eukaryotes have different anaerobic metabolic pathways to prokaryotes such as bacteria and archaea. Here we present analyses of flow-through reactor experiments showing that dissolved inorganic carbon is produced predominantly as a result of anaerobic eukaryotic metabolic activity. In our experiments, anaerobic production of dissolved inorganic carbon was consistently accompanied by large dissolved H2 production rates, suggesting the presence of fermentation. The production of both dissolved inorganic carbon and H2 persisted following administration of broad spectrum bactericidal antibiotics, but ceased following treatment with metronidazole. Metronidazole inhibits the ferredoxin/hydrogenase pathway of fermentative eukaryotic H2 production, suggesting that pathway as the source of H2 and d...
Increasing atmospheric CO2 concentrations are causing ocean acidification (OA), altering carbonat... more Increasing atmospheric CO2 concentrations are causing ocean acidification (OA), altering carbonate chemistry with consequences for marine organisms. Here we show that OA increases by 46-212% the production of phenolic compounds in phytoplankton grown under the elevated CO2 concentrations projected for the end of this century, compared with the ambient CO2 level. At the same time, mitochondrial respiration rate is enhanced under elevated CO2 concentrations by 130-160% in a single species or mixed phytoplankton assemblage. When fed with phytoplankton cells grown under OA, zooplankton assemblages have significantly higher phenolic compound content, by about 28-48%. The functional consequences of the increased accumulation of toxic phenolic compounds in primary and secondary producers have the potential to have profound consequences for marine ecosystem and seafood quality, with the possibility that fishery industries could be influenced as a result of progressive ocean changes.
Diatoms, an important group of phytoplankton, bloom annually in the Southern Ocean, covering thou... more Diatoms, an important group of phytoplankton, bloom annually in the Southern Ocean, covering thousands of square kilometers and dominating the region's phytoplankton communities. In their role as the major food source to marine grazers, diatoms supply carbon, nutrients and energy to the Southern Ocean food web. Prevailing environmental conditions influence diatom phenotypic traits (for example, photophysiology, macromolecular composition and morphology), which in turn affect the transfer of energy, carbon and nutrients to grazers and higher trophic levels, as well as oceanic biogeochemical cycles. The paucity of phenotypic data on Southern Ocean phytoplankton limits our understanding of the ecosystem and how it may respond to future environmental change. Here we used a novel approach to create a 'snapshot' of cell phenotype. Using mass spectrometry, we measured nitrogen (a proxy for protein), total carbon and carbon-13 enrichment (carbon productivity), then used this dat...
Microalgae are capable of acclimating to changes in light and ultraviolet radiation (UVR, 280-400... more Microalgae are capable of acclimating to changes in light and ultraviolet radiation (UVR, 280-400 nm). However, little is known about how the ecologically important coccolithophore Emiliania huxleyi responds to UVR when acclimated to different light regimes. Here, we grew E. huxleyi under indoor constant light or fluctuating sunlight with or without UVR, and investigated its growth, photosynthetic performance and pigmentation. Under the indoor constant light regime, the specific growth rate (μ) was highest, while fluctuating outdoor solar radiation significantly decreased the growth rate. Addition of UVR further decreased the growth rate. The repair rate of photosystem II (PSII), as reflected in changes in PSII quantum yield, showed an inverse correlation with growth rate. Cells grown under the indoor constant light regime exhibited the lowest repair rate, while cells from the outdoor fluctuating light regimes significantly increased their repair rate. Addition of UVR increased both...
The fate of diazotrophic nitrogen (N(D)) fixed by planktonic cyanobacteria in pelagic food webs r... more The fate of diazotrophic nitrogen (N(D)) fixed by planktonic cyanobacteria in pelagic food webs remains unresolved, particularly for toxic cyanophytes that are selectively avoided by most herbivorous zooplankton. Current theory suggests that N(D) fixed during cyanobacterial blooms can enter planktonic food webs contemporaneously with peak bloom biomass via direct grazing of zooplankton on cyanobacteria or via the uptake of bioavailable N(D) (exuded from viable cyanobacterial cells) by palatable phytoplankton or microbial consortia. Alternatively, N(D) can enter planktonic food webs post-bloom following the remineralization of bloom detritus. Although the relative contribution of these processes to planktonic nutrient cycles is unknown, we hypothesized that assimilation of bioavailable N(D) (e.g., nitrate, ammonium) by palatable phytoplankton and subsequent grazing by zooplankton (either during or after the cyanobacterial bloom) would be the primary pathway by which N(D) was incorpor...
Hypersaline environments pose a number of ecological and metabolic challenges to the organisms th... more Hypersaline environments pose a number of ecological and metabolic challenges to the organisms that live in them. Primary producers, such as halotolerant species of the green microalgal genus Dunaliella, are no exception. In this paper we focus on the problems posed to the acquisition and metabolism of inorganic nutrients and on the consequences of exposure to high light and UV radiation. We show that not only does growth in high salinity environments have repercussions on the flow of carbon into osmolytes such as glycerol, it also affects speciation of inorganic carbon and the uptake of inorganic ions by the cells. The strategies that Dunaliella adopt to optimize resource utilization and the interactions among metabolic pathways are also discussed.
The chlorophyte alga Dunaliella rerriolecra was exposed to UV-B radiation (UVBR) and the characte... more The chlorophyte alga Dunaliella rerriolecra was exposed to UV-B radiation (UVBR) and the characteristics of dissolved inorganic carbon (D1C)-dependent oxygen evolution, carbon fixation and CO2-concentrating mechanism (CCM) activity were examined. Exposure response measurements were ...
... Karen Kevekordes 1 , Daryl Holland 1 , Norbert HÄubner 1 , Sommer Jenkins 1 , Rebecca Koss 1 ... more ... Karen Kevekordes 1 , Daryl Holland 1 , Norbert HÄubner 1 , Sommer Jenkins 1 , Rebecca Koss 1 , Simon Roberts 1 , John A. Raven 2 , Charles M. Scrimgeour 3 , Kirsten Shelly 1 ... Badger, MR , JT Andrews , SM Whitney , M. Ludwig , DC Yellowlees , W. Leggat , and GD Price . ...
Most of the algae and cyanobacteria that have been critically examined express a carbon-concentra... more Most of the algae and cyanobacteria that have been critically examined express a carbon-concentrating mechanism (CCM) when grown at, or below, the current atmospheric CO 2 concentration. This paper considers algae that appear to lack a CCM. Critical examination of the evidence on which the presence or absence of a CCM is decided shows that more information is frequently needed before the criteria can be fully applied. Examples are the pathways of glycolate metabolism in nongreen algae, and the 13 C/ 12 C discrimination shown by form ID Rubisco in vitro. The available evidence suggests that the algae lacking CCMs are some terrestrial green microalgae, some florideophyte freshwater red macroalgae, and a number of florideophyte red macroalgae from the supralittoral, littoral, and sublittoral, and almost all of the freshwater chrysophytes and synurophytes examined. Certain environmental, biochemical , and biophysical factors may permit the occurrence of algae lacking CCMs. The absence of CCMs is presumably the plesiomorphic (i.e., ancestral) condition in cyanobacteria (and algae?). Résumé : La plupart des algues et des cyanobactéries, qui ont été examinées attentivement, possèdent un mécanisme de concentration du carbone (CCM), lorsqu'elles sont cultivées à des concentrations de CO 2 égales ou inférieures à celle de l'atmosphère. Les auteurs examinent ici les algues qui n'ont pas de CCM. Un examen critique des preuves sur lesquelles la présence ou l'absence d'un CCM est reconnue, montre qu'il faut souvent plus d'informations avant que le critère puisse être appliqué. Par exemple, on note les sentiers métaboliques du glycolate chez les algues nonvertes, et la discrimination des 13 C/ 12 C manifestée par la forme ID de la Rubisco. Les preuves actuelles suggèrent que les algues qui n'ont pas de CCM sont certaines microalgues vertes terrestres, certaines macro-algues rouges floridéophytes d'eau douce, et un nombre de macroalgues rouges floridéophytes du supralittoral, du littoral et du sublittoral, ainsi que la plupart des chrysophytes et des synurophytes d'eau douce examinées. Certains facteurs environnementaux, biochimiques et biophysiques peuvent permettre la présence d'algues dépourvues de CCM. L'absence de CCM constitue vraisembla-blement la condition plésiomorphe (c.-à-d. ancestrale), chez les cyanobactéries.
This chapter discusses two of the processes, namely photorespiration and chlororespiration, in al... more This chapter discusses two of the processes, namely photorespiration and chlororespiration, in algae that run counter to the oxygen-yielding reactions of photosynthesis and which involve the oxidation of carbohydrate and/or the consumption of oxygen. Photorespiration is associated with the oxygenase activity of Rubisco and the mechanisms by which cells recoup carbon and energy that would otherwise be lost from the
Phytoplankton life forms, including unicells, colonies, pseudocolonies, and multicellular organis... more Phytoplankton life forms, including unicells, colonies, pseudocolonies, and multicellular organisms, span a huge size range. The smallest unicells are less than 1 microm3 (e.g. cyanobacteria), while large unicellular diatoms may attain 10(9) microm3, being visible to the naked eye. Phytoplankton includes chemo-organotrophic unicells, colonies and multicellular organisms that depend on symbionts or kleptoplastids for their capacity to photosynthesize. Analyses of physical (transport within cells, diffusion boundary layers, package effect, turgor, and vertical movements) and biotic (grazing, viruses and other parasitoids) factors indicate potential ecological constraints and opportunities that differ among the life forms. There are also variations among life forms in elemental stoichiometry and in allometric relations between biovolume and specific growth. While many of these factors probably have ecological and evolutionary significance, work is needed to establish those that are most important, warranting explicit description in models. Other factors setting limitations on growth rate (selecting slow-growing species) await elucidation.
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