Two novel superoxide dismutase genes (CuZnSOD and MnSOD) in the toxic marine dinoflagellate Alexandrium pacificum and their differential responses to metal stressors

Sub-lethal effects of metals and pesticides on the freshwater dinoflagellate Palatinus apiculatus and environmental implications

Microalgae are unicellular, photosynthetic organisms in aquatic environments and are sensitive to water quality and contaminants. While green algae and diatoms are widely used for toxicity assessments, there is a relatively limited amount of toxicity data available for freshwater dinoflagellates. Here, we evaluated the sub-lethal effects of the metals Cu, Cr, Ni, and Zn and the herbicides atrazine and S-metolachlor on the freshwater dinoflagellate Palatinus apiculatus. Based on the 72-h median effective concentration (EC50), P. apiculatus showed sensitive responses to metals in the order of Cu (0.052 mg L-1), Cr (0.085 mg L-1), Zn (0.098 mg L-1), and Ni (0.13 mg L-1). Among the tested herbicides, P. apiculatus was more sensitive to atrazine (0.0048 mg L-1) than S-metolachlor (0.062 mg L-1). In addition, we observed morphological alterations and significant increases in reactive oxygen species (ROS) production in cells exposed to 0.05 mg L-1 of Cu and 0.005 mg L-1 of atrazine. These indicated that metals and pesticides induced oxidative stress in cellular metabolic processes and consequently caused severe physiological damage to the cells. Our results provide baseline data on the toxic effects of typical environmental contaminants on freshwater dinoflagellate, suggesting that P. apiculatus could be used as a bioindicator in freshwater toxicity assessments. PRACTITIONER POINTS: The sub-lethal effects of metals and pesticides on the freshwater dinoflagellate Palatinus apiculatus were evaluated. Palatinus sensitively responded to metals and pesticides; of test chemicals, atrazine (0.0048 mg L-1 of EC50) was the most sensitive. Metals and pesticides induced oxidative stress and consequently caused severe physiological damage to the Palatinus cells. The freshwater dinoflagellate Palatinus can be used as a bioindicator in freshwater toxicity assessments.

Enhancement of Docosahexaenoic Acid and Eicosapentaenoic Acid Biosynthesis in Isochrysis galbana by Bacillus jeotgali

Isochrysis galbana is valuable in aquaculture due to its production of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). However, achieving high yields of polyunsaturated fatty acids (PUFAs) presents challenges, leading to exploration of innovative approaches. This study investigated the influence of Bacillus jeotgali on the growth of I. galbana and its fatty acid composition. Co-culturing I. galbana with B. jeotgali significantly increased chlorophyll a content and cell abundance, particularly at higher bacterial population densities (algae-to-bacteria ratio of 1:10). Physiological and biochemical analyses found elevated soluble protein content in microalgae co-cultured with B. jeotgali, accompanied by decreased superoxide dismutase (SOD) activity. Fatty acid composition analysis demonstrated a distinctive profile in co-cultured I. galbana, characterized by increased PUFAs, especially EPA and DHA. Gene expression analysis indicated an upregulation of desaturase genes (d4FAD, d5FAD, d6FAD, and d8FAD) associated with PUFA synthesis pathway in I. galbana during co-culturing with B. jeotgali. This study advances our understanding of bacteria-microalgae interactions and presents a promising strategy for enhancing the production of DHA and EPA.

Two novel glutathione S-transferase (GST) genes in the toxic marine dinoflagellate Alexandrium pacificum and their transcriptional responses to environmental contaminants

The present study identified two novel glutathione S-transferase (GST) genes from the toxic dinoflagellate Alexandrium pacificum and examined their molecular characteristics and transcriptional responses to algicides and environmental contaminants. Bioinformatic analysis revealed that both ApGSTs are cytosolic, belonging to the chi-like class (ApGST1) and an undefined class (ApGST2). The overall expression of ApGSTs showed similar patterns depending on the exposed contaminants, while they were differently regulated by polychlorinated biphenyl (PCB). Copper treatments (CuCl2 and CuSO4) did not significantly induce the expression of ApGSTs. The highest up-regulations of ApGST1 and ApGST2 were under 6-h treatments of 0.10 and 0.50 mg L-1 NaOCl. Interestingly, only ApGST1 increased significantly after 0.10, 0.50, and 1.00 mg L-1 of PCB exposure (6 h). Intracellular reactive oxygen species (ROS) increased considerably under NaOCl; however, it was not significantly higher in the PCB-treated cells. GST activity was increased by NaOCl and PCB treatments, but only PCB caused apoptosis. These results suggest that GSTs are involved in the first line of phase II detoxification, protecting dinoflagellate cells against oxidative damage.

Field study of metal concentrations and biomarker responses in resident oysters of an estuarine system in southern Brazil

Pollutant exposure is considered an important factor responsible for the decline in marine biodiversity of Latin American coastal ecosystems. This threat has been detected in an estuarine system in southern Brazil, which prompted an investigation into the long-term biological effects of a chronic metal contamination on resident oysters from the Laguna Estuarine System (LES). Here, we present the species- and size-specific variations of biomarker responses (catalase, glucose-6-phosphate dehydrogenase, glutathione S-transferase, and protein carbonylation) in the gills and digestive gland of Crassostrea gigas and Crassostrea gasar. In parallel, concentrations of eight metals (Al, Cd, Cr, Cu, Fe, Mn, Pb, Zn) in soft tissues were measured. Our analyses revealed that the metal levels exhibited decreasing order in both species: Zn > Fe > Al > Cu > Mn > Cd. Except for Cu and Al, metal concentrations did not differ between oyster species. Biomarker results highlighted that C. gasar presented higher antioxidant responses, whereas C. gigas showed increased biotransformation upon exposure to LES pollutants, which varied according to the tissue. However, C. gasar showed a significant higher content of protein carbonylation but was not related to metals. In our research approach, the observation of metals presence and biomarkers-related responses are considered biologically relevant from an ecotoxicological perspective and serve as a baseline for future pollution studies in estuaries of Latin America. Finally, we recommend adopting a suite of biomarkers in both C. gasar and C. gigas, regardless their size and weight, as sentinel organisms in future regional biomonitoring studies in southern Brazil.