Effects of light and food availability on toxin production, growth and photosynthesis in Dinophysis acuminata

Abstract

Diarrhetic shellfish poisoning (DSP) toxins constitute a severe health risk to shellfish consumers and a serious economic risk to the shellfish industry. The most prominent producers of DSP toxins are the mixotrophic dinoflagellates Dinophysis spp., which rely on chloroplasts from their prey, the ciliate Mesodinium rubrum; i.e. they are kleptoplastidic. Studies based on field collected material have indicated that cellular toxin contents in Dinophysis spp. vary intraspecifically by several orders of magnitude, but the regulating factors of cellular toxin contents are still poorly understood. We isolated 7 strains of D. acuminata, all of which produced pectenotoxin-2 (PTX-2) in the range of 12.7 to 35.6 pg cell −1 when supplied with abundant nutrients, light and food. One strain was selected for detailed studies on the effects of irradiance and food availability on photoacclimation, photosynthesis, growth and toxin production. Photoacclimation was detected for the first time in this genus, indicating some genetic control of sequestered chloroplasts. Growth and photosynthesis increased 4-fold with irradiances from 7 to 130 µmol photons m −2 s −1 after a minimum of 2 wk under ample food conditions. Despite this, cellular PTX-2 content increased only slightly from (mean ± SE) 4.6 ± 0.3 to 7.8 ± 1.1 pg PTX-2 cell −1 . Toxin production continued for up to 30 d after food was depleted, leading to a build-up of toxin in D. acuminata cells to 24.7 ± 1.7 pg PTX-2 cell −1. Thus, we demonstrate that PTX-2 content is not directly coupled to irradiance and that PTX-2 production is not directly associated with ingestion of ciliate prey. Intraspecific variations in toxicity are instead most likely governed primarily by growth phase and genetic differences between different populations of Dinophysis spp.

Distribution of Dinophysis species and their association with lipophilic phycotoxins in plankton from the Argentine Sea

“…Cell concentrates of this species from New Zealand yielded much more PTX than DTX (PTX/DTX ratio >22) (MacKenzie et al, 2005). A similar situation was observed among seven strains of D. acuminata from Denmark, which produced PTX-2, whereas none produced OA or DTX (Nielsen et al, 2012). Similarly, a D. acuminata culture isolated from Eel Pond, Woods Hole, Massachusetts, USA exposed to two different irradiance treatments (dark and light) showed a cellular PTX-2 content an order of magnitude greater than that of OA and DTX-1 in both treatments (Smith et al, 2012).…”

SEASONAL AND SPATIAL PATTERNS OF TOXIGENIC SPECIES OF Dinophysis AND Pseudo-nitzschia IN A SUBTROPICAL BRAZILIAN ESTUARY

“…Because of its high cellular diarrhetic toxin content (i.e., cell quota), D. acuminata can be harmful to humans in abundances as low as 1.0 x 10³ cells L -1 (reviewed in Reguera et al, 2014). Even lower abundances can cause episodes of intoxication (e.g., 100-200 cells L -1 ; YASUMOTO et al, 1985), especially in situations that favor the retention of high toxin quotas in the cells, such as growth limitation due to the lack of prey or light (NIELSEN et al, 2012;MAFRA et al, 2014). Thus, although D. acuminata did not dominate the phytoplankton assemblage at any particular point, on several occasions the abundance of this species was greater than the alert threshold established by monitoring programs such as Brazil's (CIDASC, 2012).…”

Quantification and profiling of lipophilic marine toxins in microalgae by UHPLC coupled to high-resolution orbitrap mass spectrometry

“…To determine an appropriate concentration range for method validation, a representative environmental concentration of cells (harmful algae) was taken into account. Based on current literature [7,33,38,39], a concentration of 100 cells mL −1 was selected as a representative scenario. Production of marine toxins per cell may, however, vary and depends on various factors including light, species strain, temperature, salinity and pH [8].…”

“…However, optimized and validated analytical procedures for a simultaneous analysis of different groups of lipophilic marine toxins in algal matrix have not been reported yet and only few studies focused on the development of quantitative methods for one group of toxin [28]. Optimized extraction protocols for different dinoflagellate species have been reported, but most of them focus on a limited number of compounds within one class, single algae strains and/or single extraction steps [7,8,12,28]. To allow for an early warning of potential shellfish poisoning events through phytoplankton monitoring, a fast, general and accurate method is needed [2].…”

“…During the last decade, several algal species such as Dinophysis sp. [6][7][8], Prorocentrum sp. [9,10], Protoceratium reticulatum [11,12] and Azadinium sp.…”