Ángela Juárez

Oxidative stress and antioxidant defenses in two green microalgae exposed to copper

The aim of this work was to assess the effects of 1 week copper exposure (6.2, 108, 210 and 414microM) on Scenedesmus vacuolatus and Chlorella kessleri. The strains showed different susceptibility to copper. Copper content was determined in both strains by total X-ray reflection fluorescence analysis (TXRF). In S. vacuolatus, the increase of medium copper concentration induced an augmentation of protein and MDA content, and a significant decrease in the chlorophyll a/chlorophyll b ratio. S. vacuolatus showed a significant increase of catalase activity in 210 and 414microM of copper, and a significant increment of SOD activity and GSH content only in 414microM of copper. On the contrary, C. kessleri did not show significant differences in these parameters between 6.2 and 108microM of copper. Increased copper in the environment evokes oxidative stress and an increase in the antioxidant defenses of S. vacuolatus.

Filtration rates of the invasive pest bivalve Limnoperna fortunei as a function of size and temperature

Clearance rates of Limnoperna fortunei (Bivalvia) were investigated in laboratory experiments using monocultures of the alga Chlorella vulgaris. Experimental conditions included two mollusc sizes (15 and 23 mm), and three water temperatures (15, 20 and 25 °C) covering the normal seasonal range in the lower Paraná river and Río de la Plata estuary. Filtration rates obtained were, for the larger mussels: 9.9, 13.1 and 17.7 ml mg tissue dry weight−1 h−1 at 15, 20 and 25 °C, respectively; and for the smaller ones: 17.7, 20.8 and 29.5 ml mg−1 h−1. Differences between sizes and between temperatures (except 15 vs. 20 °C) were statistically significant. In absolute terms larger animals have higher clearance rates, but as a function of body mass smaller individuals feed more actively. Within the range of experimental values used, filtration rates were positively associated with water temperature. These clearance rates (125–350 ml individual−1 h−1) are among the highest reported for suspension feeding bivalves, including the invasive species Dreissena polymorpha, D. bugensis and Corbicula fluminea. High filtration rates, associated with the very high densities of this mollusc in the Paraná watershed (up to over 200,000 ind m−2) suggest that its environmental impact may be swiftly changing ecological conditions in the areas colonized.

Oxidative stress induced by a commercial glyphosate formulation in a tolerant strain of Chlorella kessleri

We studied the toxicity of a glyphosate formulation and provide evidence of metabolic alterations due to oxidative stress caused in a Chlorella kessleri tolerant strain by exposure to the herbicide. After 96 h of exposure to increasing concentrations of the herbicide (0-70 mg L(-1)) with alkylaryl polyglycol ether surfactant, growth was inhibited (EC50-96 h 55.62 mg L(-1)). Glyphosate increased protein and malondialdehyde content which was significantly higher than in the control at 50-70 mg L(-1). Superoxide dismutase and catalase activities and reduced glutathione levels increased in a concentration-dependant manner. Morphological studies showed increases in vacuolisation and in cell and sporangia sizes. The glyphosate formulation studied has a cytotoxic effect on C. kessleri through a mechanism that would involve the induction of oxidative stress. Upon glyphosate exposure, oxidative stress parameters such as SOD and CAT activities and MDA level could be more sensitive biomarkers than usually tested growth parameters in C. kessleri.

Dietary copper effects in the estuarine crab, Neohelice (Chasmagnathus) granulata, maintained at two different salinities.

We analyzed the dietary copper effects in the estuarine crab Neohelice (Chasmagnathus) granulata and its interaction with water salinity. Crabs were maintained at 2 per thousand and 30 per thousand salinity for 5 weeks and they were fed with commercial food supplemented with the green alga Scenedesmus vacuolatus previously exposed to copper. No mortalities were observed, but crabs maintained at 2 per thousand salinity accumulated on average 40% more copper compared to animals maintained at 30 per thousand salinity. At 2 per thousand salinity, superoxide dismutase (SOD) activity and reduced glutathione (GSH) levels were increased at the first and second weeks, respectively, while lipid peroxidation and protein oxidation were evident after 4 weeks of copper exposure. At 30 per thousand salinity, all measured variables increased progressively but were significantly higher only at the end of the assay (5th week), except for protein oxidation that remained unchanged throughout the experiment. The hepatosomatic index (HSI) was significantly decreased in response to copper exposure, but only in crabs acclimated to 2 per thousand. These findings have suggested that dietary copper exposure induces greater metal accumulation and larger oxidative stress responses in crabs maintained at 2 per thousand salinity.

A Parachlorella kessleri (Trebouxiophyceae, Chlorophyta) strain from an extremely acidic geothermal pond in Argentina

Juárez Á.B., Vélez C.G., Iñiguez A.R., Martínez D.E., Rodríguez M.C., Vigna M.S. and Ríos de Molina M.C. 2011. A Parachlorella kessleri (Trebouxiophyceae, Chlorophyta) strain from an extremely acidic geothermal pond in Argentina. Phycologia 50: 413–421. DOI: 10.2216/10-79.1 Acidic geothermal environments are rare and very few organisms can thrive in them. Chlorella or Chlorella-like species have been described in a variety of environments but their presence in extremely acidic waters have rarely been reported. A Chlorella-like alga (strain BAFC CA10) was isolated from Laguna Verde, a volcanic mesothermal acidic pond from northern Patagonia (Argentina). Applying a multimethod approach including microscopic, ultrastructural, chemical and phylogenetic analyses, the acidotolerant strain BAFC CA10 was identified as Parachlorella kessleri ( =  Chlorella kessleri) on the basis of comparisons with the authentic strain SAG 211-11g. Our results confirmed the initial characterization of the Laguna Verde strain as C. kessleri, but since this species was transferred to the new genus Parachlorella, strain BAFC CA10 should be designated as P. kessleri. Histochemical staining and sugar composition of the cell-wall amorphous and fibrillar matrix, together with transmission electron microscopy of the cells, showed the distinctive characters of the species: (1) glucosamine was the exclusive component of the fibrillar cell wall; (2) rhamnose, galactose, glucose and xylose together with minor quantities of arabinose, mannose and fucose were present in the cell-wall hemicellulose matrix; (3) there was a single parietal chloroplast surrounding the entire cell with a small aperture (“mantel-shaped”); (4) there was one pyrenoid in the thickening of the chloroplast surrounded by two starch granules and bisected by two thylakoids; and (5) the cell wall was an electron-transparent homogeneous structure 60–80 nm thick. Phylogenetic analyses of concatenated small-subunit and internal transcribed sequence ribosomal DNA sequences of coccoid green algae within the Chlorella and the Parachlorella clades of the Chlorellaceae confirmed that strain BAFC CA10 is unequivocally related to the P. kessleri strains. Our results suggest that P. kessleri should be added to the list of species capable of adapting to live in extremely acidic environments.

Improved robustness of an ethanologenic yeast strain through adaptive evolution in acetic acid is associated with its enzymatic antioxidant ability

To investigate multiple tolerance of Saccharomyces cerevisiae obtained through a laboratory strategy of adaptive evolution in acetic acid, its relation with enzymatic ROS detoxification and bioethanol 2G production.