Physiological responses of Dunaliella salina and Dunaliella tertiolecta to copper toxicity
ABSTRACT Species differences in heavy metal tolerance were investigated by comparing the responses of Dunaliella tertiolecta and Dunaliella salina to elevated concentrations of CuCl2. Although both species showed reduced cell number ml(-1) of algal culture, D. salina was more affected by increase in CuCl2. This reflects higher sensitivity of D. salina to CuCl2 compared to D. tertiolecta. Total chlorophyll in terms of microg ml(-1) was higher in D. tertiolecta at all tested CuCl2 levels, but in terms of microg cell(-1) no significant difference was observed between the two species. Total carotenoids in microg cell(-1) increased with increase in CuCl2 in both species and it was about five times higher in D. salina at all CuCl2 concentrations. While both species showed significant increase in lipid peroxidation at elevated CuCl2, the malondialdehyde content of D. salina cells was about three times higher at most CuCl2 concentrations. Although ascorbate peroxidase (APX) activity increased with increase in CuCl2 levels in both species, higher activity was observed in D. tertiolecta at all tested CuCl2 concentrations. Cu content of D. salina cells was higher than D. tertiolecta which may be due to larger volume of D. salina cells. In conclusion, since hydroxyl radical (HO*) produced from H2O2 by Cu2+ (Haber-Weiss cycle) is involved in lipid peroxidation, higher ascorbate peroxidase activity in D. tertiolecta may partly account for lower sensitivity of this species to CuCl2 compared to D. salina.
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ABSTRACT: Microalgae are sensitive indicators of environmental change and, as the basis of most freshwater and marine ecosystems, are widely used in the assessment of risk and development of environmental regulations for metals. However, interspecies differences in sensitivity to metals are not well understood. The relationship between metal-algal cell binding and copper sensitivity of marine microalgae was investigated using a series of 72-h growth-rate inhibition bioassays and short-term (1-h) uptake studies. A range of marine algae from different taxonomic groups were screened to determine whether copper adsorption to the cell membrane was influenced by biotic factors, such as the ultrastructure of cell walls and cell size. Minutocellus polymorphus was the most sensitive species to copper and Dunaliella tertiolecta the least sensitive, with 72-h IC50 values (concentration to inhibit growth-rate by 50%) of 0.6 and 530 microg Cu/L, respectively. Copper solution-cell partition coefficients at equilibrium (K(d)) were calculated for six species of algae on a per cell and surface area basis. The largest and smallest cells had the lowest and highest K(d) values, respectively (on a surface area basis), with a general (non-linear) trend of decreasing K(d) with increasing cell surface area (p=0.026), however, no relationship was found between K(d) and copper sensitivity, nor cell size and copper sensitivity. Interspecies differences in copper sensitivity were not related to cell size, cell wall type, taxonomic group or K(d) values. The differences in sensitivity may be due to differences in uptake rates across the plasma membrane, in internal binding mechanisms and/or detoxification mechanisms between the different microalgal species.Science of The Total Environment 12/2007; 387(1-3):141-54. DOI:10.1016/j.scitotenv.2007.07.016 · 3.16 Impact Factor
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ABSTRACT: High concentrations of heavy metals are typical of acidic environments. Therefore, studies on acidophilic organisms in their natural environments improve our understanding on the evolution of heavy metal tolerance and detoxification in plants. Here we sequenced the transcriptome of the extremophilic microalga Chlamydomonas acidophila cultivated in control conditions and with 500 μM of copper for 24 h. High-throughput 454 sequencing was followed by de novo transcriptome assembly. The reference transcriptome was annotated and genes related to heavy metal tolerance and abiotic stress were identified. Analyses of differentially expressed transcripts were used to detect genes involved in metabolic pathways related to abiotic stress tolerance, focusing on effects caused by increased levels of copper. Both transcriptomic data and observations from PAM fluorometry analysis suggested that the photosynthetic activity of C. acidophila is not adversely affected by addition of high amounts of copper. Up-regulated transcripts include several transcripts related to photosynthesis and carbohydrate metabolism, transcripts coding for general stress response, and a transcript annotated as homologous to the oil-body-associated protein HOGP coding gene. The first de novo assembly of C. acidophila significantly increases transcriptomic data available on extremophiles and green algae and thus provides an important reference for further molecular genetic studies. The differences between differentially expressed transcripts detected in our study suggest that the response to heavy metal exposure in C. acidophila is different from other studied green algae.Extremophiles 04/2015; 19(3). DOI:10.1007/s00792-015-0746-1 · 2.17 Impact Factor
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ABSTRACT: The concentrations of antioxidants and the activities and gene expression of antioxidant enzymes were determined in Ulva fasciata Delile by a 4-day exposure to 0, 5, 10, 20 and 50 mu M CuSO4 center dot H2O2 concentrations were increased by 50 mu M Cu, and thiobarbituric acid-reacting substance contents increased as Cu >= 20 mu M, reflecting that Cu at higher concentrations induced oxidative stress. Ascorbate and glutathione concentrations and their regeneration were not affected by excess Cu. The transcripts and activities of Mn superoxide dismutase (MnSOD; EC 126.96.36.199), FeSOD and glutathione reductase (GR; EC 188.8.131.52) increased as Cu concentrations increased. The transcripts of ascorbate peroxidase (APX; EC 184.108.40.206) increased linearly as Cu concentrations increased from 0 to 50 mu M, while its activities increased as Cu concentrations increased from 5 to 20 mu M and then remained unchanged at 50 mu M. The transcripts of catalase (CAT; EC 220.127.116.11) increased gradually as Cu concentrations increased, while CAT activities were dramatically increased by 10-50 mu M Cu. These results demonstrate that the maintenance of antioxidant homeostasis and the induction of activities of antioxidant enzymes via enhanced gene expression are used by U. fosciata to cope with the Cu-induced oxidative stress, but the defense capacity cannot sufficiently alleviate oxidative damage occurring under the condition of higher Cu concentrations.Phycologia 07/2008; 47(4):346-360. DOI:10.2216/PH07-77.1 · 1.82 Impact Factor