title: Role of dissolved nitrate and phosphate in isolates ofMesodinium rubrumand toxin-producingDinophysis acuminata.
abstract: Dinophysis acuminata, a producer of toxins associated with diarrhetic shellfish poisoning (DSP) and/or pectenotoxins (PTXs), is a mixotrophic species that requires both ciliate prey and light for growth. Linkages have been described in the literature between natural abundances of the predatorDinophysisand its prey,Mesodinium rubrum, and culture experiments have demonstrated that prey, in addition to light, is required for toxin production byDinophysis acuminata; together these suggestMesodiniumis a critical component forDinophysisgrowth and toxicity. However, little is known about the role of dissolved inorganic nutrients onMesodiniumgrowth or that of toxin-producingDinophysis. Accordingly, a series of experiments were conducted to investigate the possible uptake of dissolved nitrate and phosphate by 1)Dinophysisstarved of prey, 2)Dinophysisfeeding onMesodinium rubrum, and 3)M. rubrumgrown in nutritionally-modified media. All single-clone or mixed cultures were monitored for dissolved and particulate nutrient levels over the growth cycle, as well as growth rate, biomass, and toxin production when appropriate.D. acuminatadid not utilize dissolved nitrate or phosphate in the medium under any nutrient regime tested, i.e., nutrient-enriched and nutrient-reduced, in the absence or presence of prey, or during any growth phase monitored, i.e., exponential and plateau phases. Changes in particulate phosphorus and nitrogen inD. acuminata, were instead, strongly influenced by the consumption ofM. rubrumprey, and these levels quickly stabilized once prey were no longer available.M. rubrum, on the other hand, rapidly assimilated dissolved nitrate and phosphate into its particulate nutrient fraction, with maximum uptake rates of 1.38 pmol N/cell/day and 1.63 pmol P/cell/day. WhileD. acuminatadid not benefit directly from the dissolved nitrate and phosphate, its growth (0.37±0.01 day-1) and toxin production rates for okadaic acid (OA), dinophysistoxin-1 (DTX1) or pectenotoxin-2 (PTX2), 0.1, 0.9 and 2.6 pg /cell/day, respectively, were directly coupled to prey availability. These results suggest that while dissolved nitrate and phosphate do not have a direct effect on toxin production or retention byD. acuminata, these nutrient pools contribute to prey growth and biomass, thereby indirectly influencingD. acuminatablooms and overall toxin in the system.
authors.affiliation: Ocean College, Zhejiang University, Hangzhou, 310058, China; Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
authors.forename: Mengmeng
authors.initials: M
authors.lastname: Tong
authors.affiliation: Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA; Virginia Institute of Marine Science, College of William and Mary, Gloucester Point, VA, 23062, USA.
authors.forename: Juliette L
authors.initials: JL
authors.lastname: Smith
authors.affiliation: Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
authors.forename: David M
authors.initials: DM
authors.lastname: Kulis
authors.affiliation: Biology Department, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
authors.forename: Donald M
authors.initials: DM
authors.lastname: Anderson
keywords: Diarrhetic Shellfish Poisoning (DSP); Dinophysis acuminata; Mesodinium rubrum; dinophysistoxin (DTX); dissolved inorganic nutrients; nitrate; okadaic acid (OA); pectenotoxins (PTXs); phosphate