Dynamics and physiology of saxitoxin production by the dinoflagellatesAlexandrium spp.

Abstract

Toxin content (fmol cell-1) and a suite of elemental and macromolecular variables were measured in batch cultures of the dinoflagellates Alexandrium fundyense, A. tamarense and Alexandrium sp. from the southern New England region, USA. A different perspective was provided by semicontinuous cultures which revealed sustained, steady-state physiological adaptations by cells to N and P limitation. Two types of variability were investigated. In batch culture, changes in nutrient availability with time caused growth stage variability in toxin content, which often peaked in mid-exponential growth. A second type of variability that could be superimposed on growth stage differences is best exemplified by the high toxin content of cells grown at suboptimal temperatures. Calculations of the net rate of toxin production (Rto x; fmol cell-1 d-1) for these different culture treatments and modes made it possible to separate the dynamics of toxin production from cell division. Over a wide range of growth rates, cells produced toxin at rates approximating those needed to replace "losses" to daughter cells during division. The exception to this direct proportionality was with P limitation, which was associated with a dramatic increase in the rate of toxin production as cells stopped dividing due to nutrient limitation in batch culture. Growth stage variability in batch culture thus reflects small imbalances (generally within a factor of two) between the specific rates of toxin production and cell division. N limitation and CO z depletion both affect pathways involved in toxin synthesis before those needed for cell division; P limitation does the opposite. The patterns of toxin accumulation were the same as for major cellular metabolites or elemental pools. The highest rates of toxin production appear to result from an increased availability of arginine (Arg) within the cell, due to either a lack of competition for this amino acid from pathways involved in cell division or to increased de novo synthesis. There were no significant changes in toxin content with either acclimated growth at elevated salinity, or with short term increases or decreases of salinity. These results demonstrate that toxin production is a complex process which, under some conditions, is closely coupled to growth rate; under other conditions, these processes are completely uncoupled. Explanations for the observed variability probably relate to pool sizes of important metabolites and to the differential response of key biochemical reactions to these pool sizes and to environmental conditions.

Nitrate and phosphate supplementation to increase toxin production by the marine dinoflagellate Alexandrium tamarense

“…3). In addition, our results showed that the cellular toxin content was higher under lower phosphate conditions, which was also documented by other studies (Boyer et al, 1987;Anderson et al, 1990;Maestrini et al, 2000;Guisande et al, 2002;Frangó -pulos et al, 2004).…”

“…However, the dinoflagellate species produce a high amount of toxins under nutrient limitation. Enhanced toxin production has been observed in PSP producers under phosphorus limitation (Boyer et al, 1987;Anderson et al, 1990;Maestrini et al, 2000;Guisande et al, 2002;Frangó pulos et al, 2004) and in other toxic species under nitrogen and phosphorus limitation (Johansson and Granéli, 1999). The toxin production is a compensatory strategy to minimize the competitive disadvantages of dinoflagellates under nutrient limitation (Frangó pulos , 2004).…”

Osmotic stress triggers toxin production by the dinoflagellate Karenia brevis

“…The presence of voltage-activated Na + or Ca 2+ channels could provide a link between ion transport and brevetoxin production; however, further research is needed to identify the presence of voltage-activated channels in dinoflagellates. It is important to note that similar studies with another toxic dinoflagellate, Alexandrium fundyense, found that osmotic stress did not influence toxin production (38), which suggests that osmoregulation may differ among dinoflagellate groups.…”

Physiological and behavioral diagnostics of nitrogen limitation for the toxic dinoflagellate Alexandrium fundyense

“…. The degree to which nutrient limitation effects cellular toxicity during natural blooms is unknown, but toxin production and content have been shown to decrease in nitrogen stressed laboratory cultures (Boyer et al 1985;Anderson et al 1990a;Anderson et al 1990b;.…”