Modifications of the soluble proteome of a mediterranean strain of the invasive neurotoxic dinoflagellate Alexandrium catenella under metal stress conditions.

The soluble proteome of the mediterranean strain ACT03 of the invasive neurotoxic dinoflagellate Alexandrium catenella exposed to lead or zinc at 6, 12 or 18µM (total concentrations), or under control conditions, was characterized by two-dimensional gel electrophoresis (2-DE). Zinc reduced (P<0.05) the total number of protein spots (-41%, -52% and -60%, at 6, 12 or 18µM, respectively). Besides, most of the proteins constituting the soluble proteome were down-regulated in response to lead or zinc stresses. These proteins were involved mainly in photosynthesis (20-37% for lead; 36-50% for zinc) (ribulose-1,5-bisphosphate carboxylase/oxygenase: RUBISCO; ferredoxin-NADP+ reductase: FNR; peridinin-chlorophyll a-protein: PCP), and in the oxidative stress response (29-34% for lead; 17-36% for zinc) (superoxide dismutase: SOD; proteasome α/ß subunits). These negative effects could be partly compensated by the up-regulation of specific proteins such as ATP-synthase ß subunit (+16.3 fold after exposure to lead at 12µM). Indeed, an increase in the abundance of ATP-synthase could enrich the ATP pool and provide more energy available for the cells to survive under metal stress, and make the ATP-synthase transport of metal cations out of the cells more efficient. Finally, this study shows that exposure to lead or zinc have a harmful effect on the soluble proteome of A. catenella ACT03, but also suggests the existence of an adaptative proteomic response to metal stresses, which could contribute to maintaining the development of this dinoflagellate in trace metal-contaminated ecosystems.

Three-dimensional (3-D) fluorescence spectroscopy analysis of the fluorescent dissolved organic matter released by the marine toxic dinoflagellate Alexandrium catenella exposed to metal stress by zinc or lead.

We investigated the effects of zinc or lead on growth and on exudation of fluorescent dissolved organic matter (FDOM) by the marine toxic dinoflagellate Alexandrium catenella (Whedon & Kofoid) Balech. The species was exposed to increasing free zinc (1.34 × 10(-7) M-3.98 × 10(-6) M) or lead (5.13 × 10(-9) M-1.82 × 10(-7) M) concentra-tions. Low metal levels ([Zn(2+) ] = 1.34 × 10(-7) M; [Pb(2+) ] = 5.13 × 10(-9) M) had no effect on cell growth. Toxic effects were observed from higher metal contamination ([Zn(2+) ] = 3.98 × 10(-6) M; [Pb(2+) ] = 6.54 × 10(-8) M), as a conversion of vegetative cells into cysts. Analysis of the released FDOM by three-dimensional (3-D) fluorescence spectroscopy was achieved, using the parallel factor analysis (PARAFAC). The PARAFAC modeling revealed four components associated with two contributions: one related to the biological activity; the other linked to the organic matter decomposition in the culture medium. The C1 component combined a tryptophan peak and characteristics of humic substances, whereas the C2 component was considered as a tryptophan protein fluorophore. The two others C3 and C4 components were associated with marine organic matter production. Relea-sed fluorescent substances were induced by low ([Zn(2+) ]= 1.34 × 10(-7) M; [Pb(2+) ] = 5.13 × 10(-9) M) and moderate ([Zn(2+) ] = 6.21 × 10(-7) M; [Pb(2+) ] = 2.64× 10(-9) M) metal concentrations, suggesting the activation of cellular mechanisms in response to metal stress, to exudate FDOM that could complex metal cations and reduce their toxicity toward A. catenella cells.

Copper and cadmium effects on growth and extracellular exudation of the marine toxic dinoflagellate Alexandrium catenella: 3D-fluorescence spectroscopy approach.

In this study, metal contamination experiments were conducted to investigate the effects of copper and cadmium on the growth of the marine toxic dinoflagellate Alexandrium catenella and on the production of dissolved organic matter (Dissolved Organic Carbon: DOC; Fluorescent Dissolved Organic Matter: FDOM). This species was exposed to increasing concentrations of Cu(2+) (9.93 × 10(-10)-1.00 × 10(-7)M) or Cd(2+) (1.30 × 10(-8)-4.38 × 10(-7)M), to simulate polluted environments. The drastic effects were observed at pCu(2+)=7.96 (Cu(2+): 1.08 × 10(-8)M) and pCd(2+)=7.28 (Cd(2+): 5.19 × 10(-8)M), where cyst formation occurred. Lower levels of Cu(2+) (pCu(2+)>9.00) and Cd(2+) (pCd(2+)>7.28) had no effect on growth. However, when levels of Cu(2+) and Cd(2+) were beyond 10(-7)M, the growth was totally inhibited. The DOC released per cell (DOC/Cell) was different depending on the exposure time and the metal contamination, with higher DOC/Cell values in response to Cu(2+) and Cd(2+), comparatively to the control. Samples were also analyzed by 3D-fluorescence spectroscopy, using the Parallel Factor Analysis (PARAFAC) algorithm to characterize the FDOM. The PARAFAC analytical treatment revealed four components (C1, C2, C3 and C4) that could be associated with two contributions: one, related to the biological activity; the other, linked to the decomposition of organic matter. The C1 component combined a tryptophan peak and a characteristic humic substances response, and the C2 component was considered as a tryptophan protein fluorophore. The C3 and C4 components were associated to marine organic matter production.

Characterization of exudates released by the marine diatom Skeletonema costatum exposed to copper stress: a 3D-fluorescence spectroscopy approach.

In a laboratory study, metal contamination experiments were conducted to investigate the effects of two free copper concentrations (10(-9) and 10(-8) M) on cell growth and on dissolved organic matter exudation by a marine diatom Skeletonema costatum. Throughout incubation, the growth kinetics and exudation of extracellular molecules (i.e. dissolved organic carbon (DOC) and the fluorescent organic matter) were determined. Results revealed an inhibition of S. costatum growth when the free copper level increased (from 10(-9) to 10(-8)). Furthermore, DOC release was more significant in cultures contaminated by 10(-9) M Cu(2+) than in control, suggesting a coping mechanism developed by this species. In this study, samples were daily analysed by 3D-fluorescence and PARAFAC algorithm, in order to compare the fluorescent material produced during growth under different contaminations. PARAFAC treatment revealed two main contributions: one related to the biological activity (C1), the other linked to the marine organic matter (C2). The third component C3 was typically protein-like. This fluorophore was considered as a tryptophan-like fluorophore, whereas the C1 and the C2 components were associated to marine production such as humic matter.