CHANGES IN DOMOIC ACID PRODUCTION AND CELLULAR CHEMICAL COMPOSITION OF THE TOXIGENIC DIATOM PSEUDO‐NITZSCHIA MULTISERIES UNDER PHOSPHATE LIMITATION¹

Abstract

Production of domoic acid (DA), a neurotoxin, by the diatom Pseudo‐nitzschia multiseries (previously Nitzschia pungens f. multiseries) Hasle and its cellular chemical composition were studied in phosphate‐limited chemostat continuous cultures and in subsequent batch cultures. Under steady‐state chemostat conditions, DA production increased from 0.01 to 0.26 pg DA · cell−1· d−1 as the growth rate decreased. When the nutrient supply was discontinued (to produce a batch culture), DA production was enhanced by a factor of ca. 3. DA production was temporarily suspended upon addition of phosphate to the batch cultures but resumed 1 d later at a higher rate coincident with the decline of phosphate uptake. In both steady‐state continuous culture and batch culture, more DA was produced when alkaline phosphatase activity (APA) was high. The association of high DA production with high levels of APA and high cellular N:P ratios strongly suggests that phosphate limitation enhances DA production. Also, DA production was high when other primary metabolism (e.g. uptake of carbon, nitrogen, phosphorus and silicon, and cell division) was low, but chlorophyll a and adenosine triphosphate were generally high. This suggests that the synthesis of DA requires a substantial amount of biogenic energy.

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

“…Other studies also have observed measurable levels of DA prior to the onset of stationary growth, e.g. in P. australis (Garrison et al, 1992), P. multiseries (Pan et al, 1996a;Radan, 2008;Thessen et al, 2009) and P. fraudulenta (Thessen et al, 2009). P. cuspidata even exhibited greater cellular DA in the exponential phase relative to stationary phase when N, not Si or P, was the macronutrient inducing the onset of stationary growth (Auro, 2007).…”

Bacterial community composition differs with species and toxigenicity of the diatom Pseudo-nitzschia

“…In comparison, many strains of species including P. delicatissima, P. pungens, and open-ocean Pseudo-nitzschia have not been documented to produce DA, or else produce DA at low levels (as low as fg DA cell -1 ) (Bates et al 1998, Bates 2000, Lundholm et al 2006, Marchetti et al 2008, Trick et al 2010. For a single strain in culture, DA levels within the medium typically are highest when cell growth is limited by silicic acid (Bates et al 1991, Pan et al 1996b, phosphate (Pan et al 1996a), or iron (Rue & Bruland 2001, Maldonado et al 2002. Exponentially growing Pseudo-nitzschia cells can also produce enhanced levels of DA when using urea as a nitrogen source in comparison to inorganic nitrogen sources (Howard et al 2007), and field studies have documented DA production by nutrient-replete Pseudo-nitzschia cells (Marchetti et al 2004).…”

Domoic acid: The synergy of iron, copper, and the toxicity of diatoms

“…examined to date with highly sensitive, enzyme-linked immunosorbent assay (ELISA)-based analytical methods have been found, at one time or another, to produce the toxin domoic acid (DA). However, the factors regulating toxin production are not known, and toxin concentrations in a given species can vary from high to undetectable in both laboratory cultures (e.g., Pan et al 1996;Maldonado et al 2002) as well as in natural waters (e.g., Trainer et al 2000Trainer et al , 2002. Early research indicated that growth limitation by silicon (Si) and phosphorus (P) would increase cell toxicity after prolonged senescence (Bates et al 1991;Pan et al 1996).…”

“…However, the factors regulating toxin production are not known, and toxin concentrations in a given species can vary from high to undetectable in both laboratory cultures (e.g., Pan et al 1996;Maldonado et al 2002) as well as in natural waters (e.g., Trainer et al 2000Trainer et al , 2002. Early research indicated that growth limitation by silicon (Si) and phosphorus (P) would increase cell toxicity after prolonged senescence (Bates et al 1991;Pan et al 1996). Subsequent findings have shown that cell toxicity during exponential growth is stimulated by low iron availability, resulting in the release of DA to solution, which, in turn, increases rates of iron uptake (Maldonado et al 2002).…”