Molybdate:sulfate ratio affects redox metabolism and viability of the dinoflagellate Lingulodinium polyedrum

MoaE Is Involved in Response to Oxidative Stress in Deinococcus radiodurans

Molybdenum ions are covalently bound to molybdenum pterin (MPT) to produce molybdenum cofactor (Moco), a compound essential for the catalytic activity of molybdenum enzymes, which is involved in a variety of biological functions. MoaE is the large subunit of MPT synthase and plays a key role in Moco synthesis. Here, we investigated the function of MoaE in Deinococcus radiodurans (DrMoaE) in vitro and in vivo, demonstrating that the protein contributed to the extreme resistance of D. radiodurans. The crystal structure of DrMoaE was determined by 1.9 Å resolution. DrMoaE was shown to be a dimer and the dimerization disappeared after Arg110 had been mutated. The deletion of drmoaE resulted in sensitivity to DNA damage stress and a slower growth rate in D. radiodurans. The increase in drmoaE transcript levels the and accumulation of intracellular reactive oxygen species levels under oxidative stress suggested that it was involved in the antioxidant process in D. radiodurans. In addition, treatment with the base analog 6-hydroxyaminopurine decreased survival and increased intracellular mutation rates in drmoaE deletion mutant strains. Our results reveal that MoaE plays a role in response to external stress mainly through oxidative stress resistance mechanisms in D. radiodurans.

Oxidative stress and toxicology of Cu2+ based on surface areas in mixed cultures of green alga and cyanobacteria: The pivotal role of H2O2

The toxicity of heavy metals in algal monocultures is well studied and is mediated by reactive oxygen and nitrogen species (ROS/RNS). However, little is known about the toxicity of heavy metals and the mechanisms involved in mixed cultures. Here we examine the oxidative stress and toxic effects of Cu²⁺ on the green alga Dunaliella salina (DS) and the cyanobacteria Synecochoccus elongatus (SE) in both mono- and mixed cultures. We find that both species benefit in mixed cultures and acquire higher resistance to Cu²⁺ toxicity, with a particularly marked effect on SE. DS has a larger surface area than SE, so increases in the number of DS cells compared to SE diminishes the proportion of SE surface area exposed to Cu²⁺, and contributes to increasing cyanobacterial resistance in mixed cultures. However, these mixed cultures also display as an unexpected property an increased resistance of DS in mixed cultures. SE and DS cells showed significant differences on the kinetics of H₂O₂ production and antioxidant capacities. The integrated (overall) redox response of mixed cultures, in terms of total amount of H₂O₂ produced, was proportional to the total surface area of algal species exposed to Cu²⁺, independent of algal composition in mixed systems. However, mixed cultures display emergent properties, as the time course of H₂O₂ accumulation is not a simple function of the composition of the mixed cultures. Emergent properties are also observed in the speed of membrane lipid oxidation by the two species, as measured using mixed cultures in which only one of the two species is labeled using the membrane oxidation indicator C₁₁-BODIPY^581/591. We suggest that, in addition to H₂O₂¸ other redox signals (e.g. NO) and allelochemicals (auxins, cytokinins, etc.) may be used to construct a complex inter-species communication network. This could allow mixed algal systems, whatever their composition, to integrate their cellular responses and perform as a coherent unit against toxic Cu²⁺ ions.

Interactive effects of spectral quality and trace metal availability on the growth of Trichodesmium and Symbiodinium

Light and trace metals are critical growth factors for algae but how the interdependence of light quality and metal availability affects algal growth remains largely unknown. Our previous studies have demonstrated the importance of Ni and Fe on the growth of Trichodesmium and Symbiodinium, respectively, two important marine primary producers inhabiting environments with high light intensities. Here, we investigated the effects of light quality and intensity with availability of either Ni or Fe on their growth. For Trichodesmium, we found that specific growth rates for high Ni treatments were all significantly higher than in corresponding low Ni treatments with varying light quality and intensity. The inhibitory effect of low intensity red light was also countered by sufficient Ni supply. For Symbiodinium, we found that growth rates and biomass were reduced by 75% under low intensity red light and the stress can only be partially relieved by sufficient Fe supply. The results show that trace metal availability plays an important role in relieving the stress induced by low red light condition for both Trichodesmium and Symbiodinium although the cyanobacterium performs better in this growth condition. The difference may be attributed to the presence of phycocyanin, a unique pigment attuned to absorption of red light, in Trichodesmium. Our study shows that the concerted effects of light intensity and quality compounded with trace metal availability may influence the growth of photosynthetic organisms in the ocean.