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Collos, Y., Jauzein, C., Laabir, M., & Vaquer, A. (2013). Discrepancies between net particulate carbon production and 13C-labelled bicarbonate uptake by Alexandrium catenella (Dinophyceae): grazing controls the balance between autotrophic and non autotrophic carbon acquisition1. Journal of Phycology, 49(3), 441–446.
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Collos, Y., Jauzein, C., Ratmaya, W., Souchu, P., Abadie, E., & Vaquer, A. (2014). Comparing diatom and Alexandrium catenella/tamarense blooms in Thau lagoon: Importance of dissolved organic nitrogen in seasonally N-limited systems. Harmful Algae, 37, 84–91.
Résumé: Diatom blooms in Thau lagoon are always related to rain events leading to inputs of inorganic nutrients such as phosphate, ammonium and nitrate through the watershed with time lags of about 1 week. In contrast, blooms of Alexandrium catenella/tamarense can occur following periods of 3 weeks without precipitation and no significant input of conventional nutrients such as nitrate and phosphate. Field results also indicate a significant drop (from 22–25 to 15–16 μM over 3 days) in dissolved organic nitrogen (DON) at the bloom peak, as well as a significant inverse relationship between A. catenella/tamarense cell density and DON concentrations that is not apparent for diatom blooms. Such dinoflagellate blooms are also associated with elevated (6–9 μM) ammonium concentrations, a curious feature also observed by other investigators, possibly the results of ammonium excretion by this organism during urea or other organic nitrogen assimilation. The potential use of DON by this organism represents short cuts in the nitrogen cycle between plants and nutrients and requires a new model for phytoplankton growth that is different from the classical diatom bloom model. In contrast to such diatom blooms that are due to conventional (nitrate, phosphate) nutrient pulses, Alexandrium catenella/tamarense blooms on the monthly time scale are due to organic nutrient enrichment, a feature that allows net growth rates of about 1.3 d−1, a value higher than that generally attributed to such organisms.
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Fertouna-Bellakhal, M., Dhib, A., Fathalli, A., Bellakhal, M., Chomérat, N., Masseret, E., et al. (2015). Alexandrium pacificum Litaker sp. nov (Group IV): Resting cyst distribution and toxin profile of vegetative cells in Bizerte Lagoon (Tunisia, Southern Mediterranean Sea). Harmful Algae, 48, 69–82.
Résumé: Abstract
A high spatial resolution sampling of Alexandrium pacificum cysts, along with sediment characteristics (% H2O, % organic matter (OM), granulometry), vegetative cell abundance and environmental factors were investigated at 123 study stations in Bizerte Lagoon (Tunisia). Morphological examination and ribotyping of cells obtained from a culture called ABZ1 obtained from a cyst isolated in lagoon sediment confirmed that the species was A. pacificum. The toxin profile from the ABZ1 culture harvested during exponential growth phase was simple and composed of the N-sulfocarbamoyl toxins C1 (9.82 pg toxin cell−1), the GTX6 (3.26 pg toxin cell−1) and the carbamoyl toxin Neo-STX (0.38 pg toxin cell−1). The latter represented only 2.8% of the total toxins in this strain. High abundance of A. pacificum cysts correlated with enhanced percentages of water and organic matter in the sediment. In addition, sediment fractions of less than 63 μm were examined as a favorable potential seedbed for initiation of future blooms and outbreaks of A. pacificum in the lagoon. A significant difference in the cyst distribution pattern was recorded among the lagoon's different zones, with the higher cyst abundance occurring in the inner waters. Also, no correlation due to the specific hydrodynamics of the lagoon was observed in the spatial distribution of A. pacificum cysts and vegetative cells.
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Hadjadji, I., Frehi, H., Ayada, L., Abadie, E., & Collos, Y. (2014). A comparative analysis of Alexandrium catenella/tamarense blooms in Annaba Bay (Algeria) and Thau lagoon (France); phosphorus limitation as a trigger. Comptes Rendus Biologies, 337(2), 117–122.
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Jean, N., Dumont, E., Herzi, F., Balliau, T., Laabir, M., Masseret, E., et al. (2017). Modifications of the soluble proteome of a mediterranean strain of the invasive neurotoxic dinoflagellate Alexandrium catenella under metal stress conditions. Aquat. Toxicol., 188, 80–91.
Résumé: The soluble proteome of the mediterranean strain ACT03 of the invasive neurotoxic dinoflagellate Alexandrium catenella exposed to lead or zinc at 6, 12 or 18 mu M (total concentrations), or under control conditions, was characterized by two-dimensional gel electrophoresis (2-DE). Zinc reduced (P < 0.05) the total number of protein spots (-41%, -52% and -60%, at 6, 12 or 18 M, respectively). Besides, most of the proteins constituting the soluble proteome were down-regulated in response to lead or zinc stresses. These proteins were involved mainly in photosynthesis (20-37% for lead; 36-50% for zinc) (ribulose-1,5-bisphosphate carboxylase/oxygenase: RUBISCO; ferredoxin-NADP(+) reductase: FNR; peridinin-chlorophyll a-protein: PCP), and in the oxidative stress response (29-34% for lead; 17-36% for zinc) (superoxide dismutase: SOD; proteasome alpha/beta subunits). These negative effects could be partly compensated by the up-regulation of specific proteins such as ATP-synthase beta subunit (+16.3 fold after exposure to lead at 12 M). Indeed, an increase in the abundance of ATP-synthase could enrich the ATP pool and provide more energy available for the cells to survive under metal stress, and make the ATP-synthase transport of metal cations out of the cells more efficient. Finally, this study shows that exposure to lead or zinc have a harmful effect on the soluble proteome of A. catenella ACT03, but also suggests the existence of an adaptative proteomic response to metal stresses, which could contribute to maintaining the development of this dinoflagellate in trace metal-contaminated ecosystems.
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