Changes in toxin content, biomass and pigments of the dinoflagellate Alexandrium minutum during nitrogen refeeding and growth into nitrogen or phosphorus stress

Abstract

Two stralns of the paralytic shellfish tox~n (PST) producing dinoflagellate Alexandrium lninutum Halim (highly toxic ALlV and weakly toxic AL2V) were grown in batch culture with either nitrate or phosphate as the limiting nutrient. In comparison with cells of the strain ALlV, cells of AL2V grew at a similar C-specific rate, had a higher C/N ratio, and lower ratios of chl a/chl c2 and chl a/peridinin. Neither chlorophylls nor carotenoids could be used to estimate C-biomass, N-biomass or toxin content for this organism. The toxin profile for both strains was dominated (up to 95 %) by the gonyautoxin GTX4, with smaller proportions of GTX1. GTX2 and GTX3. The rate of toxin synthesis for both strains was greatest 1 to 2 d after the N-refeeding of N-deprived cells, with the net rate of toxin synthesis exceeding that of C-biomass and cell division by a factor of up to 4. Toxin synthesis was not enhanced by short-term P-stress. N-stress alone led to a decrease in toxin cell-', but P-stress followed by N-stress did not result in such a decline, implicating phosphorus in the regulation of toxin metabolism. Although arginine is a major precursor for PST synthesis, taurine, glycine, glutamine, and cell N showed similar relations to that observed for arginine with respect to toxin content. Furthermore, the mole ratio of arginine/toxin could vary by a factor of up to 5 between ALlV and AL2V at peak values of toxin cell-', and by more than 5 within a strain when growing under different conditions. These observations suggest that the relationship between free arginine content and toxin content is complex. No explanation for the higher toxin content of A L l V IS apparent, except that ALlV has a higher N-content per cell and this may be conducive to a higher rate of synthesis of the N-rich toxins.

Grazer-induced toxin formation in dinoflagellates: a transcriptomic model study

“…The main challenge in both these approaches is the inherent difficulty in discerning the differences leading to the different toxin levels from those due to unrelated physiological effects. The predator-induced differences in PSP toxin accumulation provide a system in which samples of the same strain with substantially different toxin quotas can be compared without resorting to severe P-starvation to increase cell toxin quota, or to application of other harsh conditions known to lead to a reduction in PSP toxin content (Flynn et al, 1994;Hwang & Lu, 2000;Touzet et al, 2007).…”

Chemical and Physical Factors Influencing Toxin Content

“…In general, changes in toxin content are associated with disturbed (unbalanced) physiology, with the up-shock or down-shock of cells exiting or entering stationary phases (Anderson 1994;Flynn et al 1994Flynn et al , 1996Granéli 1999a, 1999b;Granéli et al 1998;Edvardsen et al 1990, cited in Granéli et al 1998). Toxin production in normal experiments can be difficult to measure against a background of changing cell biomass, cell size and indeed toxin leakage or catabolism.…”

“…Nonetheless, depending on the chemical composition of the toxin, different treatments may be expected to have different impacts. Thus N-rich PSP-toxins are synthesized during N-upshock and P-stress (which gives relatively high N-status) and not during N-downshock (Flynn et al 1994;Granéli et al 1998). Table 18.1 illustrates the importance of up/down shock events in affecting toxicity.…”

“…Also, the dinoflagel-late G. catenatum has been shown to increase its intracellular toxin concentration under P deficiency (Boyer et al 1987, cited in Cembella 1998Flynn et al 1996). Synthesis of N-containing toxins (such as DA and PSP) declines under N stress (Bates et al 1991, cited in Bates 1998Boyer et al 1987, cited in Cembella 1998, and increases after reintroduction of N (Bates et al 1991, cited in Bates 1998Flynn et al 1994). Toxin content in A. excavatum (Levasseur et al 1995, cited in Granéli et al 1998 and P. multiseries (Bates et al 1993, cited in Bates 1998) has also been shown to increase when N is available in high concentration, but even more so if ammonium is used as a N source rather than nitrate (Levasseur et al 1995, cited in Granéli et al 1998.…”

Positive effects of continuous low nitrate levels on growth and photosynthesis of Alexandrium tamarense (Gonyaulacales, Dinophyceae)

“…Blooms of A. tamarense have been recorded in many oceanic regions and have attracted concern from around the world (Glibert et al 1988;Ichimi et al 2001;Weise et al 2002). Because strong relationships appear to exist between algal blooms and nutrient enrichment, numerous studies have been carried out on the nutrients that affect growth and toxin production of A. tamarense and other dinoflagellate species, and have especially focused on nitrogen and phosphorus supply (Boyer et al 1987;Flynn et al 1994;Yamamoto & Tarutani 1999;John & Flynn 2000). Most studies agreed that nitrogen or phosphorus restriction reduced population growth of dinoflagellates, although its effects on toxin productivity are more complicated (Siu et al 1997;Flynn 2002b;Wang & Hsieh 2002).…”