| 1. |
- Persson, Agneta, 1963, et al.
(författare)
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Differences in Specific Mass Density Between Dinoflagellate Life Stages and Relevance to Accumulation by Hydrodynamic Processes
- 2021
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Ingår i: Journal of Phycology. - : Wiley. - 0022-3646 .- 1529-8817. ; 57:5, s. 1492-1503
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Tidskriftsartikel (refereegranskat)abstract
- One previously unstudied aspect of differences between sexual and asexual life stages in large-scale transport and accumulation is density (mass per unit volume) of cells in each life stage. The specific density was determined for Scrippsiella lachrymosa cells in medium with and without nitrogen (N) enrichment through density-gradient centrifugation. Growth medium without N addition is often called "encystment medium" when used for the purpose of resting cyst formation in cyst-forming dinoflagellates; mating gametes are usually seen after 2-3 days. Significant differences in specific density were found after 2 days in encystment medium simultaneously with the observation of typical gamete swimming behavior and mating. The specific density of cells in encystment medium was 1.06 g center dot cm(-3); whereas, the specific density of cells in growth medium was 1.11 g center dot cm(-3). Cells in encystment medium were found to have significantly increased lipid content, reduced chlorophyll content, and reduced internal complexity. The findings may explain differential transport of less dense and chemotactically aggregating gametes into surface blooms in contrast to denser vegetative cells that perform daily vertical migration and do not aggregate. Passive accumulation of non-migrating gametes into layers in stagnant water also can be explained, as well as sinking of zygotes when the storage of highly dense starch increases. Resting cysts had a density of over 1.14 g center dot cm(-3) and would sink to become part of the silt fraction of the sediment. We suggest that differences in behavior and buoyancy between sexual and asexual life stages cause differences in cell accumulation, and therefore large-scale, environmental transport could be directly dependent upon life-cycle transitions.
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| 2. |
- Persson, Agneta, 1963, et al.
(författare)
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Differences in swimming pattern between life cycle stages of the toxic dinoflagellate Alexandrium fundyense
- 2013
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Ingår i: Harmful Algae. - : Elsevier BV. - 1568-9883. ; 21-22, s. 36-43
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Tidskriftsartikel (refereegranskat)abstract
- Different life stages of Alexandrium fundyense have different swimming behavior; gametes often are said to "swarm" or "dance" before mating. This behavior was studied, and quantitative measures of these motility patterns in two-dimensions were generated using motion-analysis software applied to video records of individual-cell movements. Behavior, swimming patterns, and growth were studied in two strains of A. fundyense and compared in encystment medium and growth medium. Vegetative cells swam straight, rotating around the apical axis until they hit something and then swam straight in a different direction. Gamete swimming behavior was slower and characterized by frequent direction changes and circular motion. Gametes contacted other cells frequently (>5 cell contacts min(-1) cell(-1)). Zygotes swam slowly when newly formed and later became nearly immobile; these cells continued to contact other cells and also surfaces. The results are in accordance with field observations of long swimming distances for vegetative cells, accumulation in thin layers of gametes, and sinking of developing resting cysts attached to marine snow for zygotes. (C) 2012 Elsevier B.V. All rights reserved.
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| 3. |
- Persson, Agneta, 1963, et al.
(författare)
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Dinoflagellate gamete formation and environmental cues: Observations, theory, and synthesis
- 2008
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Ingår i: Harmful Algae. - : Elsevier BV. - 1568-9883. ; 7:6, s. 798-801
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Tidskriftsartikel (refereegranskat)abstract
- For some species of cyst-producing dinoflagellates, the sexual life cycle is well studied in laboratory cultures. Dinoflagellate blooms in stratified waters, vertical migration of vegetative cells, and the accumulation of populations within thin layers are well-documented phenomena in nature. We propose a conceptual model that places these phenomena in a functional, ecological context: vegetative cells of a dinoflagellate population display vertical migration, but at the end of the bloom, environmental or internal cues shift the cell cycle to gamete formation. Then the vertical migrations cease, and cells accumulate in a layer at the pycnocline where gametes fuse to form zygotes, which then sink to the sediment as resting cysts. We support this conceptual model with experimental and environmental evidence. (C) 2008 Elsevier B.V. All rights reserved.
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| 4. |
- Persson, Agneta, 1963, et al.
(författare)
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Toxin content differs between life stages of Alexandrium fundyense (Dinophyceae)
- 2012
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Ingår i: Harmful Algae. - : Elsevier BV. - 1568-9883. ; 19:-, s. 101-107
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Tidskriftsartikel (refereegranskat)abstract
- Different life stages of two mating-compatible clones of the paralytic shellfish toxin (PST)-producing dinoflagellate Alexandrium fundyense Balech were separated using a combination of techniques; culturing and sampling methods were used to separate vegetative cells and gametes, and sorting flow cytometry was used to separate zygotes. PST profiles were significantly different between life stages; the two gonyautoxins GTX1 and 2 were present in vegetative and senescent cells, but disappeared from gametes and zygotes. Toxin-profile changes were shown to occur very quickly in both strains when pellicle cyst formation was induced by shaking (four minutes) followed by rinsing on a screen. These pellicle cysts produced from exponentially-growing, vegetative cells lost GTX1 and 2 completely. Rapid toxin epimerization of GTX1 to GTX4 and GTX2 to GTX3 is one possible explanation, although the biological advantage of this remains unclear. Another possible explanation is that during the mating phase of a bloom or when cells are disturbed, GTX1 and GTX2 are released into the surrounding water. It may be advantageous for a dinoflagellate bloom to be surrounded by free toxins in the water. (c) 2012 Elsevier B.V. All rights reserved.
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| 5. |
- Persson, Agneta, 1963, et al.
(författare)
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Grazing on toxic Alexandrium fundyense resting cysts and vegetative cells by the eastern oyster (Crassostrea virginica)
- 2006
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Ingår i: Harmful Algae. - : Elsevier BV. - 1568-9883. ; 5:6, s. 678-684
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Tidskriftsartikel (refereegranskat)abstract
- In laboratory experiments, oysters (Crassostrea virginica) were fed Alexandrium fundyense (strain CB501) vegetative cells or resting cysts (from strains CB501 and GMT25) produced from laboratory cultures. The toxicity per cyst was 1.7 pg STXequiv/cyst and for vegetative cells 3.9 pg STXequiv/cell. The toxic, resting cysts and vegetative cells were removed from suspension in the experimental containers within about 4 h. Oysters fed toxic vegetative cells digested 72% of cells ingested, and 28% survived gut passage by forming temporary cysts. Toxin levels of oysters fed vegetative cells averaged 27 μg STXequiv/100 g meat. Resting cysts added to the experimental containers adhered to the walls so that only 40% of the cysts added were available to the oysters during the experiment. Of the cysts that were ingested, approximately 59% were digested, and oysters accumulated toxins (an average of 1.2 μg STXequiv/100 g meat), showing that consumption of resting cysts can cause toxicity in oysters. Direct consumption of resting cysts, thus, may explain shellfish toxicity in areas without known blooms, but with toxic resting cysts in the sediment. These results suggest a possible role of toxic cysts in mediating time-lags between surface blooms and appearance of toxicity in benthic grazers, and the possible role of benthic grazers in controlling seed populations, except in anoxic areas, which can serve as cyst “refuges” from grazing mortality.
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| 6. |
- Persson, Agneta, 1963, et al.
(författare)
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Sexual life stages and temperature dependent morphological changes allow cryptic occurrence of the Florida red tide dinoflagellate Karenia brevis
- 2013
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Ingår i: Harmful Algae. - 1568-9883. ; 30, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- Karenia brevis, the Florida red tide dinoflagellate, has been studied extensively, but very little attention has been paid to its sexual life cycle. We found that the life cycle of K. brevis is heterothallic, most probably not resting cyst-producing, but with life stages of different morphology. The isogamous gametes were slightly smaller than vegetative cells and not as broad and flat. The late zygote was yellow-brown in appearance with a thicker wall and more rounded shape lacking carina. Pellicle cysts of these zygotes closely resembled the few earlier descriptions of "possible cysts" of the species. In addition, temperature-dependent, morphological changes and pellicle-cyst formation were observed. Cells placed in the cold (15 degrees C) formed spherical, thin-walled pellicle cysts that germinated into cells that were round in cross-section and longer than wide - so morphologically different from vegetative cells that they would not be correctly identified if encountered in field samples. Cells grown at 25 degrees C were wider and flatter than cells grown at 20 degrees C. Cells warmed from cold conditions became flat and wide within hours, returning to the typical shape. Also the morphological differences between sexual life stages were large enough to allow misidentification and cryptic occurrence of K. brevis. The cell shape of K. brevis was not fixed, but could vary from very wide and flat to elongate with rounded cross-section in the same culture of clonal cells and in the same cells within a short time (hours). In addition to the culture studies, sediment samples from a Karenia "hot spot" area were concentrated, and the dinoflagellate cyst fraction was investigated for resting cysts. Cysts were not found, and Karenia cells did not germinate from slurry cultures of the concentrated cyst fraction. (C) 2013 Elsevier B.V. All rights reserved.
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| 7. |
- Persson, Agneta, 1963, et al.
(författare)
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The Eastern mudsnail, Ilyanassa obsoleta, actively forages for, consumes, and digests cysts of the dinoflagellate, Scrippsiella lachrymosa
- 2008
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Ingår i: Malacologia. - 0076-2997. ; 50:1-2, s. 341-345
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Tidskriftsartikel (refereegranskat)abstract
- The Eastern mudsnail, Ilyanassa obsoleta, was attracted to, consumed, and digested resting cysts of the dinoflagellate Scrippsiella lachrymosa when cysts were presented in grazing experiments. Twenty snails were observed individually for one hour in petri dishes divided into four parts wherein cysts were present in one quadrant, sediment particles of the same size range were in another quadrant, and two quadrants were free of particles. Actively foraging snails were nearly twice as likely to be found in quadrants containing S. lachrymosa cysts as in the other quadrants until cysts were consumed. Microscope observations of fecal pellets from snails feeding on cysts revealed digestive destruction of the cysts. These findings indicate that deposit-feeding grazers can actively seek dinoflagellate cysts as a food item, thereby influencing distribution of cysts and subsequent germination of dinoflagellate vegetative cells.
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| 8. |
- Sauvage, Justine, et al.
(författare)
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Bacterial exudates as growth-promoting agents for the cultivation of commercially relevant marine microalgal strains
- 2022
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Ingår i: Journal of the World Aquaculture Society. - : Wiley. - 0893-8849 .- 1749-7345. ; 53:6, s. 1101-1119
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Tidskriftsartikel (refereegranskat)abstract
- In laboratory and industrial cultivation of marine microalgae, it is customary to enrich cultures with macronutrients (N, P), chelated trace metals, and vitamins at similar to 10(4) x concentrations found in nature to obtain high culture densities. Other naturally occurring growth-promoting compounds found in local seawater are not enriched and remain at environmental concentrations. Microalgae may thus be deprived of the mutualistic contributions of co-occurring microorganisms with which they have evolved complex chemical relationships. In the present study, we assess the direct (mixed bacteria-microalgae cultivation) and indirect (exposure to exudates only, without physical contact) effects of 10 bacterial strains on the growth of five marine microalgal strains used as feeds in marine aquaculture hatcheries. Bacterial strains were selected based upon previously reported growth-promoting characteristics in plants or microalgae, or known release of probiotics. Our experiments demonstrate superior stimulation of microalgal growth by bacterial exudates, and without the presence of the bacteria that produced these exudates. However, response to bacterial exudate enrichment was dependent upon the microalgae strain and bacterial pairing. Exudates from Bacillus, Mesorhizobium, arid Phaeobacter strains were most effective, with 22%-69% increases in microalgal specific growth rate. Such findings indicate that bacterial exudates accelerate rate-limiting processes governing nutrient acquisition, assimilation, or anabolism, and possibly algal release of exopolymeric substances. Maximal cell density, however, remained constrained by macronutrient limitation. Scaledup trials in an oyster hatchery confirmed the practical benefit of bacterial exudate culture medium enrichment and demonstrated the suitability of exudate-enriched microalgae to feed hatchery-reared bay scallops. This work presents a promising strategy to improve microalgal culture media formulations using bacterial exudate components as growth promoters, and is the first such study to identify specific pairings with relevance for aquaculture production.
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| 9. |
- Sauvage, Justine, et al.
(författare)
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Biodegradable, metal-chelating compounds as alternatives to EDTA for cultivation of marine microalgae
- 2021
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Ingår i: Journal of Applied Phycology. - : Springer Science and Business Media LLC. - 0921-8971 .- 1573-5176. ; 33, s. 3519-3537
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Tidskriftsartikel (refereegranskat)abstract
- Iron (Fe) is an essential nutrient for microalgal metabolism. The low solubility of Fe in oxic aquatic environments can be a growth-limiting factor for phytoplankton. Synthetic chelating agents, such as ethylenediaminetetraacetic acid (EDTA), are used widely to maintain Fe in solution for microalgal cultivation. The non-biodegradable nature of EDTA, combined with sub-optimal bioavailability of Fe-EDTA complexes to microalgae, indicates opportunity to improve microalgal cultivation practices that amplify production efficiency and environmental compatibility. In the present study, the effects of four organic chelating ligands known to form readily bioavailable organic complexes with Fe in natural aquatic environments were investigated in relation to growth and biochemical composition of two marine microalgae grown as live feeds in shellfish hatcheries (Chaetoceros calcitrans and Tisochrysis lutea). Three saccharides, alginic acid (ALG), glucuronic acid (GLU), and dextran (DEX), as well as the siderophore desferrioxamine B (DFB), were compared to EDTA. Organic ligands characterized by weaker binding capacity for cationic metals (i.e., ALG, GLU, DEX) significantly improved microalgal growth and yields in laboratory-scale static batch cultures or bubbled photobioreactors. Maximal microalgal growth enhancement relative to the control (e.g., EDTA) was recorded for GLU, followed by ALG, with 20-35% increase in specific growth rate in the early stages of culture development of C. calcitrans and T. lutea. Substitution of EDTA with GLU resulted in a 27% increase in cellular omega 3-polyunsaturetd fatty acid content of C. calcitrans and doubled final cell yields. Enhanced microalgal culture performance is likely associated with increased intracellular Fe uptake efficiency combined with heterotrophic growth stimulated by the organic ligands. Based upon these results, we propose that replacement of EDTA with one of these organic metal-chelating ligands is an effective and easily implementable strategy to enhance the environmental compatibility of microalgal cultivation practices while also maximizing algal growth and enhancing the nutritional quality of marine microalgal species commonly cultured for live-feed applications in aquaculture.
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| 10. |
- Sauvage, Justine, et al.
(författare)
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Effect of pluronic block polymers and N-acetylcysteine culture media additives on growth rate and fatty acid composition of six marine microalgae species
- 2021
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 0175-7598 .- 1432-0614. ; 105, s. 2139-2156
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Tidskriftsartikel (refereegranskat)abstract
- The efficiency of microalgal biomass production is a determining factor for the economic competitiveness of microalgae-based industries. N-acetylcysteine (NAC) and pluronic block polymers are two compounds of interest as novel culture media constituents because of their respective protective properties against oxidative stress and shear-stress-induced cell damage. Here we quantify the effect of NAC and two pluronic (F127 and F68) culture media additives upon the culture productivity of six marine microalgal species of relevance to the aquaculture industry (four diatoms-Chaetoceros calcitrans, Chaetoceros muelleri, Skeletonema costatum, and Thalassiosira pseudonana; two haptophytes-Tisochrysis lutea and Pavlova salina). Algal culture performance in response to the addition of NAC and pluronic, singly or combined, is dosage- and species-dependent. Combined NAC and pluronic F127 algal culture media additives resulted in specific growth rate increases of 38%, 16%, and 24% for C. calcitrans, C. muelleri, and P. salina, respectively. Enhanced culture productivity for strains belonging to the genus Chaetoceros was paired with an similar to 27% increase in stationary-phase cell density. For some of the species examined, culture media enrichments with NAC and pluronic resulted in increased omega-3-fatty acid content of the algal biomass. Larval development (i.e., growth and survival) of the Pacific oyster (Crassostrea gigas) was not changed when fed a mixture of microalgae grown in NAC- and F127-supplemented culture medium. Based upon these results, we propose that culture media enrichment with NAC and pluronic F127 is an effective and easily adopted approach to increase algal productivity and enhance the nutritional quality of marine microalgal strains commonly cultured for live-feed applications in aquaculture.
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