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Metal ecotoxicity testing with microalgae is subject to interferences such as change in bioavailable metal fraction by excreted metabolites. Moreover, high metal loads are usually necessary for obtaining 50% effect concentration (EC50) values based on cell number or chlorophyll a. Thus, sensitive parameters, which promptly respond to low dissolved metal variations at environmentally relevant concentrations, are much needed. The genus Scenedesmus, a coenobium-forming freshwater microalga, is cosmopolitan and inhabits pristine and contaminated waters. The present investigation addressed cellular phenotypic alterations in Scenedesmus acuminatus (Largerheim) Chodat 1902 caused by the presence of copper. Copper toxicity to the alga was investigated under laboratory-controlled conditions using a concentration range of 10-8 mol 1-1 to 10-3 mol 1-1 total dissolved Cu2+, thus including environmentally relevant concentrations. Free Cu2+ concentrations were determined using an ion-selective electrode calibrated with a metal ion buffer. The phenotypic plasticity of S. acuminatus was measured as the number of cells per coenobia and found to be readily affected at low copper concentrations. Under healthy conditions (10-8 mol 1-1 total dissolved Cu2+, 10-11 mol 1-1 free Cu2+) S. acuminatus formed eight-celled coenobia, whereas at 10-7 mol 1-1 total dissolved Cu2+ (3 × 10-10 mol 1-1 free Cu2+) these were absent and at 10-5 mol 1-1 total dissolved Cu2+ (5 × 10-8 mol 1-1 free Cu2+) free cells were predominant. Chlorophyll a synthesis was affected by 5 × 10-8 mol 1-1 free Cu-2+ or higher. EC50 (3.3 × 10-5 mol 1-1 free Cu2+) was obtained using chlorophyll a values after 96-h exposure to the toxicant. The number of cells per coenobia was a more sensitive parameter than chlorophyll a to assess Cu toxicity, and at concentrations that may be encountered in the environment. [ABSTRACT FROM AUTHOR]

The filamentous desmid Spondylosium panduriforme (Heimerl) Teiling var. panduriforme f. limneticum (West & west) Teiling (Desmidiaceae)strain 072CH-UFCAR, is surrounded by a well-defined, mucilaginous capsule consisting of a capsular polysaccharide (CPS). This microalga also produces an extracellular polysaccharide. Analysis of the carbohydrate composition of the two polymers by gas chromatography showed that they were different. Both were composed of galactose fucose xylose, arabinose, rhamnose, and glucose but in different amounts. For example, glucuronic acid accounts for 24% of the EPS material but only traces were found in the CPS. Significant difference were also found during methylation analysis. Fucose appeared to have a higher degree of branching in the EPS than in the CPS. These branches were located on C-3 and could be the position for the attachment of the glucuronic acid was present as 1→ 4linked and terminal units. A possible explanation for the formation of the EPS is suggested. [ABSTRACT FROM AUTHOR]