chlorophyll-a and domoic-acid

The toxigenic diatom Pseudo-nitzschia multiseries Hasle, isolated from the U.S. Pacific Northwest, was examined in unialgal laboratory cultures and in natural assemblages during shipboard experiments, to examine cellular growth and domoic acid (DA) production as a function of nitrogen (N) substrate and availability expected during bloom development and decline. Laboratory experiments utilizing batch cultures conducted at saturating (120 μmol photons m

Topics: Cell Culture Techniques; Chlorophyll; Diatoms; Kainic Acid; Marine Toxins; Nitrogen

In order to assess the effects of Fe-enrichment on the growth and domoic acid (DA) production of the toxigenic diatom

Topics: Allelopathy; Cell Culture Techniques; Cells, Cultured; Chlorophyll; Chlorophyll A; Diatoms; Humans; Iron; Kainic Acid; Marine Toxins; Neurotoxins; Seafood

The effects of inorganic and organic nitrogen supply on the growth and domoic acid (DA) production of Pseudo-nitzschia cf. seriata and Pseudo-nitzschia calliantha from Bizerte Lagoon (SW Mediterranean Sea) were studied during field and laboratory experiments. Nitrogen enrichments (40 µM NO3 (-); 10 µM NH4 (+); 20 µM CH4N2O) and a control, with no added N, were carried out in separate carboys with seawater collected from Bizerte Lagoon. In the field experiments, all N-enrichments resulted in significant increases in chlorophyll a concentration, and maintained exponential growth until the end of the experiment. The initial diatom community was dominated by a bloom of P. cf. seriata (9.3 × 10(5) cells l(-1)). After 6 days of incubation, the abundance of P. cf. seriata was greatest in the urea addition (1.52 × 10(6) cells l(-1)), compared to the ammonium treatment (0.47 × 10(6) cells l(-1)), nitrate treatment (0.70 × 10(6) cells l(-1)) and control (0.36 × 10(6) cells l(-1)). The specific growth rates, calculated from increases in chlorophyll a and cell abundance, were statistically different across all treatments, with the highest in the urea and nitrate additions. Similar results were obtained from the laboratory experiments. These were carried out with P. calliantha isolated from Bizerte Lagoon and grown in f/2 medium enriched with 40 µM nitrate, 10 µM ammonium and 20 µM urea. The exponential growth rate was significantly faster for the cells cultured with urea (1.50 d(-1)) compared to the nitrate (0.90 d(-1)) and ammonium (0.80 d(-1)) treatments and the control (0.40 d(-1)). Analysis of DA, performed at the beginning and the end of the both experiments in all treatments, revealed very low concentrations (below the limit of quantification, 0.02- 1.310(-7) pg cell(-1), respectively).The field and laboratory experiments demonstrate that P.cf. seriata and P. calliantha are able to grow efficiently on the three forms of N, but with a preference for urea.

Topics: Chlorophyll; Chlorophyll A; Diatoms; Kainic Acid; Marine Toxins; Mediterranean Sea; Nitrates; Nitrogen; Seawater; Water Pollutants, Chemical

In spring/summer 2015, a toxic bloom by the diatom Pseudo-nitzschia (PN) occurred along the west coast of the United States which led to closures of the harvest of razor clams and Dungeness crabs. Twice monthly observations of temperature, salinity, nutrients, chlorophyll and phytoplankton species composition allowed us to track oceanographic conditions preceding and during the development of the bloom. PN cells were first detected during late winter 2015. A PN bloom was initiated following the onset of coastal upwelling in mid-April; subsequent peaks in May and June were sustained by episodic upwelling events and reached magnitudes of 105 cells/L and 106 cells/L, 40% and 90% of the total diatom abundance, respectively. The bloom temporarily crashed in July due to a lack of upwelling, but PN cells increased again in August due to a resumption of upwelling, albeit with lower magnitude. Macronutrient conditions prior to this bloom likely played a critical role in triggering the bloom and its toxicity (particularly silicic acid limitation stress). Nutrient stress preceding the toxic bloom was related to two oceanographic events: an anomalously warm and thick water mass that occupied the northern North Pacific from September 2014 through 2015 leading to a highly-stratified water column, and the drawdown of nitrate and silicic acid during an unusually intense winter phytoplankton bloom in February and early March 2015.

Topics: Chlorophyll; Diatoms; Kainic Acid; Nitrates; Oregon; Salinity; Seasons; Silicic Acid; Temperature

Bacteria are known to influence domoic acid (DA) production by Pseudo-nitzschia spp., but the link between DA production and physiology of diatoms requires more investigation. We compared a toxic P. multiseries to a non-toxic P. delicatissima, investigating links between DA production, physiological parameters, and co-occurring bacteria. Bacterial communities in cultures of both species were reduced by antibiotic treatment, and each of the diatoms was inoculated with the bacterial community of the other species. The physiology of P. delicatissima was minimally affected by the absence of bacteria or the presence of alien bacteria, and no DA was detected. P. multiseries grew faster without bacteria, did not produce a significant amount of DA, and exhibited physiological characteristics of healthy cells. When grown with alien bacteria, P. multiseries did not grow and produced more DA; the physiology of these cells was affected, with decreases in chlorophyll content and photosynthetic efficiency, an increase in esterase activity, and almost 50% mortality of the cells. The alien bacterial community had morphological and cellular characteristics very different from the original bacteria, and the number of free-living bacteria per algal cell was much higher, suggesting the involvement of bacteria in DA production.

Topics: Anti-Bacterial Agents; Bacteria; Cell Physiological Phenomena; Chlorophyll; Diatoms; Kainic Acid; Marine Toxins; Photosynthesis; Species Specificity

Microalgae have differing sensitivities to copper toxicity. Some species within the genus Pseudo-nitzschia produce domoic acid (DA), a phycotoxin that has been hypothesised to chelate Cu and ameliorate Cu toxicity to the cells. To better characterise the effect of Cu on Pseudo-nitzschia, a toxic strain of P. multiseries and a non-toxic strain of P. delicatissima were exposed to Cu(II) for 96 h (50 μg l(-1) for P. delicatissima and 50, 100 and 150 μg l(-1) for P. multiseries). Physiological measurements were performed daily on Pseudo-nitzschia cells using fluorescent probes and flow cytometry to determine the cell density, lipid concentration, chlorophyll autofluorescence, esterase activity, percentage of dead algal cells, and number of living and dead bacteria. Photosynthetic efficiency and O(2) consumption and production of cells were also measured using pulse amplitude modulated fluorometry and SDR Oxygen Sensor dish. The DA content was measured using ELISA kits. After 48 h of Cu exposure, P. delicatissima mortality increased dramatically whereas P. multiseries survival was unchanged (in comparison to control cells). Cellular esterase activity, chlorophyll autofluorescence, and lipid content significantly increased upon Cu exposure in comparison to control cells (24h for P. delicatissima, up to 96 h for P. multiseries). Bacterial concentrations in P. multiseries decreased significantly when exposed to Cu, whereas bacterial concentrations were similar between control and exposed populations of P. delicatissima. DA concentrations in P. multiseries were not modified by Cu exposure. Addition of DA to non-toxic P. delicatissima did not enhance cells survival; hence, extracellular DA does not protect Pseudo-nitzschia spp. against copper toxicity. Results suggested that cells of P. delicatissima are much more sensitive to Cu than P. multiseries. This difference is probably not related to the ability of P. multiseries to produce DA but could be explained by species differences in copper sensitivity, or a difference of bacterial community between the algal species.

Topics: Animals; Cell Survival; Chelating Agents; Chlorophyll; Copper; Diatoms; Esterases; Flow Cytometry; Kainic Acid; Water Pollutants, Chemical

Diatoms of the genus Pseudo-nitzschia are potentially toxic microalgae, whose blooms can trigger amnesic shellfish poisoning. The purpose of this study was to test and adapt different probes and procedures in order to assess the physiological status of Pseudo-nitzschia multiseries at the cell level using flow cytometry. To perform these analyses, probes and procedures were first optimized for concentration and incubation time. The percentage of dead Pseudo-nitzschia cells, the metabolic activity of live cells and their intracellular lipid content were then measured following a complete growth cycle. In addition, chlorophyll autofluorescence and efficiency of photosynthesis (quantum yield) were monitored. The concentration and viability of bacteria present in the medium were also assessed. Domoic acid (DA) was quantified as well. Just before the exponential phase, cells exhibited high metabolic activity, but low DA content. DA content per cell became most abundant at the beginning of the exponential phase when lipid storage was high, which provided a metabolic energy source, and when they were surrounded by a high number of bacteria (high bacteria/P. multiseries ratio). These physiological measurements tended to decrease during exponential phase and until stationary phase, at which time P. multiseries cells did not contain any DA nor store any lipids, and started to die.

Topics: Aquatic Organisms; Bacteria; Bacterial Load; Cell Survival; Chlorophyll; Diatoms; Flow Cytometry; Fluorescence; Kainic Acid; Lipids; Marine Toxins; Microscopy, Fluorescence; Shellfish Poisoning

Oceanic high-nitrate, low-chlorophyll environments have been highlighted for potential large-scale iron fertilizations to help mitigate global climate change. Controversy surrounds these initiatives, both in the degree of carbon removal and magnitude of ecosystem impacts. Previous open ocean enrichment experiments have shown that iron additions stimulate growth of the toxigenic diatom genus Pseudonitzschia. Most Pseudonitzschia species in coastal waters produce the neurotoxin domoic acid (DA), with their blooms causing detrimental marine ecosystem impacts, but oceanic Pseudonitzschia species are considered nontoxic. Here we demonstrate that the sparse oceanic Pseudonitzschia community at the high-nitrate, low-chlorophyll Ocean Station PAPA (50 degrees N, 145 degrees W) produces approximately 200 pg DA L(-1) in response to iron addition, that DA alters phytoplankton community structure to benefit Pseudonitzschia, and that oceanic cell isolates are toxic. Given the negative effects of DA in coastal food webs, these findings raise serious concern over the net benefit and sustainability of large-scale iron fertilizations.

Topics: Chlorophyll; Climate Change; Copper; Diatoms; Ecosystem; Iron; Kainic Acid; Marine Toxins; Neurotoxins; Nitrates; Seawater