Effects of Ammonium and Nitrate on Growth and Domoic Acid Production by Nitzschia pungens in Batch Culture (original) (raw)
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The amount of urea used as fertilizer in agriculture has tripled over the last four last decades. This nutrient is discharged in large quantities from rivers to coastal waters, and is used as food by many microalgae. Previous studies have shown that numerous toxic species can assimilate both organic and inorganic nitrogen. This has also been proposed by some researchers as a potential cause of the increased occurrence of some diatom species of the genus Pseudo-nitzschia that produce domoic acid, a neurotoxin that can contaminate shellfish. Moreover, higher domoic acid content has been reported for P. austra/is in the presence of urea. We investigated the influence of urea on the content of domoic acid in P. mu/tiseries and P. pungens. Our results showed that, in batch cultures, P. muftiseries contains more toxin per cell in the presence of urea. In continuous cultures, substitution of nitrates by urea increases the cellular toxin content of P. pungens. These findings suggest the imp...
Marine Drugs, 2014
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.
Photosynthesis and growth of Nitzschia pungens f. multiseries Hasle, a neurotoxin producing diatom
Journal of Experimental Marine Biology and Ecology, 1991
The pennate diatom Nitzschia pungens f. multiseries Hasle implicated in the amnesic shellfish poisoning in bays of eastern Prince Edward Island, produces a neurotoxin, domoic acid. Batch cultures of this diatom were grown at photosynthet,_'¢ photon flux densities (PPFD) of 1100 (high light, HL) and 105 (low light, LL) #mol m -2 s-~ at 10 °C. The relationships between photosynthesis and PPFD were established on Days 1,4, 8, 15, 25 and 34 and were quantitatively described. Maximum specific growth rates (#max) for the HL and LL cultures were 0.74 and 0.56 day-~ respectively. Cells grown ~t HL had higher assimilation number (Pmn: 2.2 #g C [#g Chl a] -~ h-~) but lower initial slopes (gn: 6.06 ng C [#g Chl a] -I1-! [#mol m-2 s-t] --l)than those grown at LL (ProS: 1.7 #g C [#g Chl a] -i h-~; 0ta: 8.69 ng C [#g Chl a] -i h -~ [#tool m -2 s -~] -~ ). Both Pm B and 0t n increased from Day 1 to Day 4, and then decreased as the cells aged. Temporal variations in the rate of growth, cellular Chl a, cell concentration, carbon and nitrogen showed differences in their magnitude and lag phase.
Environmental Monitoring and Assessment, 2017
Pseudo-nitzschia is a diatom genus capable of producing the neurotoxin domoic acid (DA), which has been related to mortalities of marine vertebrates, and the amnesic shellfish poisoning (ASP) in human consumers of contaminated bivalves. This study reports DA production among Pseudo-nitzschia strains isolated from shellfish farming areas in southern Brazil. Twenty-seven cultures of potentially toxigenic Pseudonitzschia species were established. Growth, steppedchain formation, and DA production were evaluated in static, intermittently illuminated (12:12 photoperiod) batch cultures for 12 selected strains, and under continuous light and/or turbulence for a single Pseudonitzschia calliantha strain. Growth rate ranged from 0.16 to 0.39 day −1 among the 12 strains. Only P. calliantha and P. cf. multiseries yielded detectable levels of intracellular DA, reaching up to 0.054 fg cell −1 in late exponential and 0.15 pg cell −1 in early stationary phase, respectively. Continuous light impaired cell growth, and turbulence enhanced step-chain formation by threefold during exponential growth phase, but no DA production was detected under both conditions. The effect of turbulence on chain formation should be further evaluated in the field, once particle size is expected to affect the ingestion of toxic cells and thus toxin accumulation by certain DA vectors. The low cell toxicity revealed herein under laboratory conditions is in accordance with the low frequency of DA contamination episodes in south Brazilian waters. Nevertheless, monitoring of Pseudo-nitzschia abundance and DA presence in farming areas is continuously required to assure the quality of local shellfish products.
Marine Drugs, 2013
Because domoic acid, a neurotoxic secondary metabolite produced by marine diatoms in the genus Pseudo-nitzschia, is hypothesized to be part of a high affinity iron uptake system, we investigated whether domoic acid could improve the competitive ability of Pseudo-nitzschia delicatissima, and whether the availability of iron changed the outcome of competition experiments. We found that domoic acid had a slight negative effect on growth of the diatom Skeletonema marinoi when it was grown in monocultures. However, when S. marinoi was cultured with P. delicatissima the presence of domoic acid resulted in a reduction of S. marinoi cells by up to 38% and an increase in P. delicatissima cell numbers by up to 17% under iron replete conditions. Similar effects were not observed in low iron treatments. Domoic acid was not taken up by P. delicatissima cells. Overall, our results indicate that domoic acid can improve the competitive ability of Pseudo-nitzschia spp. and that iron is likely to be involved. This study provides an unusual example of indirect inhibition of competitor growth mediated by a secondary metabolite.
Marine drugs, 2017
In order to assess the effects of Fe-enrichment on the growth and domoic acid (DA) production of the toxigenic diatom , static cultures that received the addition of different iron (Fe) concentrations were maintained for 30 days. Intra- and extracellular DA concentrations were evaluated over time, and growth and chain-formation were compared to those of non-toxic diatoms, sp. Growth rates of (μ = 0.45-0.73 d) were similar among cultures containing different Fe concentrations. Likewise, the similar incidence and length of stepped cell chains (usually 2-4; up to 8-cell long) among the treatments reinforces that the cultures were not growth-inhibited under any condition tested, suggesting an efficient Fe acquisition mechanism. Moreover, DA concentrations were significantly higher under the highest Fe concentration, indicating that Fe is required for toxin synthesis. sp. reached comparable growth rates under the same Fe concentrations, except when the dissolved cell contents from a cult...