SURFACTANT PROMOTION OF THE INHIBITORY EFFECTS OF CUPRIC GLUTAMATE ON THE DINOFLAGELLATE ALEXANDRIUM(1)

Bioluminescence and toxicity as driving factors in harmful algal blooms: Ecological functions and genetic variability

Dinoflagellates are an ecologically important group of marine microbial eukaryotes with a remarkable array of adaptive strategies. It is ironic that two of the traits for which dinoflagellates are best known, toxin production and bioluminescence, are rarely linked when considering the ecological significance of either. Although dinoflagellate species that form some of the most widespread and frequent harmful algal blooms (HABs) are bioluminescent, the molecular and eco-evolutionary associations between these two traits has received little attention. Here, the major themes of biochemistry and genetics, ecological functions, signaling mechanisms, and evolution are addressed, with parallels and connections drawn between the two. Of the 17 major classes of dinoflagellate toxins, only two are produced by bioluminescent species: saxitoxin (STX) and yessotoxin. Of these, STX has been extensively studied, including the identification of the STX biosynthetic genes. While numerous theories have been put forward as to the eco-evolutionary roles of both bioluminescence and toxicity, a general consensus is that both function as grazing deterrents. Thus, both bioluminescence and toxicity may aid in HAB initiation as they alleviate grazing pressure on the HAB species. A large gap in our understanding is the genetic variability among natural bloom populations, as both toxic and non-toxic strains have been isolated from the same geographic location. The same applies to bioluminescence, as there exist both bioluminescent and non-bioluminescent strains of the same species. Recent evidence demonstrating that blooms are not monoclonal events necessitates a greater level of understanding as to the genetic variability of these traits among sub-populations as well as the mechanisms by which cells acquire or lose the trait, as sequence analysis of STX+ and STX- species indicate the key gene required for toxicity is lost rather than gained. While the extent of genetic variability for both bioluminescence and toxicity among natural HAB sub-populations remains unknown, it is an area that needs to be explored in order to gain greater insights into the molecular mechanisms and environmental parameters driving HAB evolution.

Inhibition of copper uptake in yeast reveals the copper transporter Ctr1p as a potential molecular target of saxitoxin

Saxitoxin is a secondary metabolite produced by several species of dinoflagellates and cyanobacteria which targets voltage-gated sodium and potassium channels in higher vertebrates. However, its molecular target in planktonic aquatic community members that co-occur with the toxin producers remains unknown. Previous microarray analysis with yeast identified copper and iron-homeostasis genes as being differentially regulated in response to saxitoxin. This study sought to identify the molecular target in microbial cells by comparing the transcriptional profiles of key copper and iron homeostasis genes (CTR1, FRE1, FET3, CUP1, CRS5) in cells exposed to saxitoxin, excess copper, excess iron, an extracellular Cu(I) chelator, or an intracellular Cu(I) chelator. Protein expression and localization of Ctr1p (copper transporter), Fet3p (multicopper oxidase involved in high-affinity iron uptake), and Aft1p (iron regulator) were also compared among treatments. Combined transcript and protein profiles suggested saxitoxin inhibited copper uptake. This hypothesis was confirmed by intracellular Cu(I) imaging with a selective fluorescent probe for labile copper. On the basis of the combined molecular and physiological results, a model is presented in which the copper transporter Ctr1p serves as a molecular target of saxitoxin and these observations are couched in the context of the eco-evolutionary role this toxin may serve for species that produce it.

Toxicity of the amphoteric surfactant, cocamidopropyl betaine, to the marine macroalga, Ulva lactuca

The degradation of the synthetic, amphoteric surfactant, cocamidopropyl betaine (CAPB) and its toxicity to the marine macroalga, Ulva lactuca, has been evaluated using several different physiological test end-points over different periods of exposure up to 120 h. Droplet surface angle measurements revealed that, following a period of acclimation of about 24 h, CAPB began to degrade and that primary degradation was complete within 120 h. Effective quantum yield (∆F/F(m)') and relative growth rates (RGRs) were the most sensitive measures of phytotoxicity, with CAPB concentrations at and above 10 mg l(-1) eliciting irreversible, time-dependent and/or dose-dependent responses. Cell membrane damage, estimated from measurements of ion leakage, was detected only at a concentration of 40 mg l(-1) after 48 h of exposure to CAPB but by 120 h damage was evident at all measured concentrations above 10 mg l(-1). These observations suggest that both CAPB and its metabolites are intrinsically toxic to U. lactuca. The findings of this study are discussed in terms of the environmental consequences of applying CAPB to control harmful algal blooms.