Effects of silicate limitation on production of domoic acid, a neurotoxin, by the diatom Pseudo-nitzschia multiseries. I. Batch culture studies

Abstract

ABSTRACT. Dornoic acid (DA) production by Pseudo-nitzschia multiseries (Hasle) was studied at various silicate concentrations and under silicate perturbation. Both slowly dividing and non-dividing population~ produced DA, and the production rates were inversely correlated with the ambient silicate concentrations. Production of DA was significantly enhanced when overall cell metabolism (i.e growth rate) declined as a result of silicate stress. Following silicate starvation, cultures supplemented with silicate registered uptake, but suspended DA production. Results suggest that luxury uptake of Si by P. multisenes may happen only in phys~ologically active populations, i.e, the exponential phase, but not in the stationary phase. There were 2 stages of DA production The first stage corresponded to a decline in growth caused by moderately low lcvels of remaining s~licate in the medium, wh.ile the second stage was caused by severe silicate limitation. The production rate during the second stage (13.67 to 30.20 fg DA cell-' d-') was about an order of magnitude higher than during the first stage (0.97 to 4.98 fg DA cell-' d-l). Increases and decreases in cellular DA content corresponded to decreases and increases in growth rates.KEY WORDS: Domoic acid . Pseudo-nitzschia multiseries . Silicate limitation . Batch culture INTRODUCTIONPseudo-nitzschia multiseries, formerly known as Pseudonitzschia pungens f. multiseries (Hasle, 1995), produces domoic acid (DA), which has caused amnesic shellfish poisoning (ASP) in Atlantic Canada (Addison & Stewart 1989). The ASP problem has now been observed on both the Atlantic and Pacific coasts of North America (Fritz et al. 1992, Garrison et al. 1992. Studies on DA production have shown it to occur only during the stationary phase, coinciding with low levels of silicate in the medium (Subba Rao et al. 1990, Bates et al. 1991, Pan et al. 1991). These observations suggest a possible relationship between silicate limitation and DA production. However, direct linkage between DA production and silicon depletion is unlikely, as silicate is neither a component of DA nor apparently involved in its synthesis.The magnitude of a diatom bloom is often directly related to the availability of silicon in sea water. Silicon regulates the growth and frustule formation of diatoms. Decreases in silicate concentrations to low or undetectable levels in marine and freshwater habitats during diatom blooms have been well documented (Paasche 1973a, Sommer & Stabel 1983, Egge & Aksnes 1992, Harrison et al. 1993.In cultures, silicate concentrations in the medium may regulate the yield of diatom cells (Taguchi et al. 1987). Cessation of cell division, which may be due to cessation of DNA synthesis (Darley & Volcani 1969, Sullivan & Volcani 1973, was found to accompany depletion of silicon in the culture medium (Lewin 1955, Lewin & Chen 1968, Vaulot et al. 1987, Brzezinski et al. 1990. Bates et al. (1991) first showed a connection between silicate limitation and DA production. Two of their 5 treatments with low s...

Intra- and interspecies differences in growth and toxicity of Pseudo-nitzschia while using different nitrogen sources

“…In CLN47 and Pn-12, there is evidence of toxin production during late exponential phase, similar to results for P. pseudodelicatissima (Pan et al 2001), P. australis (Garrison et al 1992) and for P. multiseries (Pan et al 1996a). A possible explanation for DA production in late exponential phase, before the culture has stopped growing, is that this phase may be a period of transition, when some cells have stopped dividing and are producing DA while others are still growing (Pan et al 1996a, Bates 1998. High DA content during lag phase is probably from the inoculum used to start the culture; however, it is possible that the shock of being transferred led to DA production in lag phase cultures (Bates 1998).…”

“…Many Pseudo-nitzschia culture studies present results from one strain (Bates et al 1991, Douglas & Bates 1992, Hillebrand & Sommer 1996, Pan et al 1996a,b, Fehling et al 2004, Armstrong Howard et al 2007. Others compare one strain of multiple species (Jackson et al 1992, Maldonado et al 2002, Fehling et al 2005.…”

Establishing the link between <em>Ostreopsis</em> cf.<em>ovata</em> blooms and human health impacts using ecology and epidemiology

“…As has been observed in toxin producing microalgae, toxin cell concentrations may vary with the physiological phase as well as in response to environmental forcings (e.g. Bates et al 1991, Pan et al 1996, Taroncher-Oldenberg et al 1997, although the response can be speciesspecific. For instance, in laboratory experiments (Bolli et al 2007), paralytic shellfish toxin cell content in Alexandrium catenella and A. minutum decreased from the exponential to the stationary phase, and it was also lower under turbulent than calm conditions.…”

Pseudo-nitzschia physiological ecology, phylogeny, toxicity, monitoring and impacts on ecosystem health

“…These demonstrated that DA production is usually minimal or nondetectable during exponential growth in batch cultures, and increases during the stationary phase as cell division slows as a result of either Si or P limitation. Similarly, studies have shown a reciprocal relationship between growth rate and DA production in Si- (Bates et al, 1996;Pan et al, 1996b;Kudela et al, 2004a) or Plimited continuous cultures of this species (Pan et al, 1996c;Hagströ m et al, 2011). An exception to the pattern of minimal or non-detectable DA during fast growth is P. cf.…”