title: Molybdate:sulfate ratio affects redox metabolism and viability of the dinoflagellate Lingulodinium polyedrum.
abstract: Molybdenum is a transition metal used primarily (90% or more) as an additive to steel and corrosion-resistant alloys in metallurgical industries and its release into the environment is a growing problem. As a catalytic center of some redox enzymes, molybdenum is an essential element for inorganic nitrogen assimilation/fixation, phytohormone synthesis, and free radical metabolism in photosynthesizing species. In oceanic and estuarine waters, microalgae absorb molybdenum as the water-soluble molybdate anion (MoO4(2-)), although MoO4(2-) uptake is thought to compete with uptake of the much more abundant sulfate anion (SO4(2-), approximately 25 mM in seawater). Thus, those aspects of microalgal biology impacted by molybdenum would be better explained by considering both MoO4(2-) and SO4(2-) concentrations in the aquatic milieu. This work examines toxicological, physiological and redox imbalances in the dinoflagellate Lingulodinium polyedrum that have been induced by changes in the molybdate:sulfate ratios. We prepared cultures of Lingulodinium polyedrum grown in artificial seawater containing eight different MoO4(2-) concentrations (from 0 to 200 μM) and three different SO4(2-) concentrations (3.5 mM, 9.6 mM and 25 mM). We measured sulfur content in cells, the activities of the three major antioxidant enzymes (superoxide dismutase, catalase, and ascorbate peroxidase), indexes of oxidative modifications in proteins (carbonyl content) and lipids (thiobarbituric acid-reactive substances, TBARS), the activities of the molybdenum-dependent enzymes xanthine oxidase and nitrate reductase, expression of key protein components of dinoflagellate photosynthesis (peridinin-chlorophyll a protein and ribulose-1,5-biphosphate carboxylase/oxidase) and growth curves. We find evidence for Mo toxicity at relatively high [MoO4(2-)]:[SO4(2-)] ratios. We also find evidence for extensive redox adaptations at Mo levels well below lethal levels.
authors.affiliation: Postgraduate Program in Health Science (Environmental Chemistry), CBS, Universidade Cruzeiro do Sul, 08060070 São Paulo, SP, Brazil. Electronic address: marcelo.barros@cruzeirodosul.edu.br.
authors.forename: M P
authors.initials: MP
authors.lastname: Barros
authors.forename: H C
authors.initials: HC
authors.lastname: Hollnagel
authors.forename: A B
authors.initials: AB
authors.lastname: Glavina
authors.forename: C O
authors.initials: CO
authors.lastname: Soares
authors.forename: D
authors.initials: D
authors.lastname: Ganini
authors.forename: S
authors.initials: S
authors.lastname: Dagenais-Bellefeuille
authors.forename: D
authors.initials: D
authors.lastname: Morse
authors.forename: P
authors.initials: P
authors.lastname: Colepicolo
mesh_terms: D004141:Dinoflagellida / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism / Q000502:physiology; D004789:Enzyme Activation / Q000187:drug effects; D008982:Molybdenum / Q000737:chemistry / Q000633:toxicity*; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000187:drug effects*; D013431:Sulfates / Q000737:chemistry / Q000378:metabolism*; D014969:Xanthine Oxidase / Q000235:genetics
chemical_list: D013431:Sulfates; C044659:molybdate; D008982:Molybdenum; D014969:Xanthine Oxidase
keywords: AAS; APX; ASW; Algal bloom; CAT; DNPH; EC(50); Gonyaulax; Harmful algae; LD(50); LS/ASW; MDA; MoCo; Molybdenum; NO; NR; ONOO(−); Oxidative stress; PCP; Peridinin; ROS/RNS; Rubisco; SOD; TBARS; VLS/ASW; XO; [Mo]:[sulfate]; artificial seawater; ascorbate peroxidase; atomic absorption spectroscopy; catalase; concentration ratio between molybdate and sulfate; dinitrophenylhydrazine; effect dose for 50% population; lethal dose for 50% population; low sulfate concentration seawater; malondialdehyde; molybdenum-dependent cofactor; nitrate reductase; nitric oxide; peridinin complex-protein; peroxynitrite; reactive oxygen/nitrogen species; ribulose-1	5-biphosphate carboxylase/oxidase; superoxide dismutase; thiobarbituric acid-reactive substances; very low sulfate concentration seawater; xanthine oxidase