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Heavy Metal Toxicity in a N_2-Fixing Cyanobacterium, anabaena doliolum: Regulation of Toxicity by Certain Environmental Factors

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Biomedical and Environmental Sciences 1990年第2期3卷 240-249页

作者： S.K.DUBEY L.C.RAI Laboratory of Algal Biology Centre of Advanced Study in BotanyBanaras Hindu University Varanasi-221005 India

The toxic effects of chromium and tin salts on growth, ^(14)C uptake, heterocyst differentiation, and nitrate reductase. nitrogenase, and glutamine synthetase activities of anabaena doliolum and their regulation by pH. salinity, extracellular metabolites (spent), and organic acids have been studied. The toxicity of the test metals was lowered at alkaline pH and increased at acidic pH. NaCl at 20 mM was found to decrease metal toxicity. Extracellular metabolites (spent) in a 1:1 ratio(v/v) with fresh culture medium and organic acids were found to reduce metal toxicity. Among the various organic acids studied, humic acid was the most effective in regulating metal toxicity, apparently due to its multiple binding sites for metal cations. This study demonstrated that environmental *** as pH, salinity, extracellular metabolites, and organic acids, can mediate the toxicity of heavy metals to A. doliolum in a laboratory microcosm, (C)1990 Academic Press. Inc.

关键词： anabaena doliolum

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Protective Effects of Certain Natural and Synthetic Complexans on the Toxicity of Chromium and Tin to a N_2-Fixing Cyanobacterium, anabaena doliolum

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Biomedical and Environmental Sciences 1989年第3期2卷 271-281页

作者： LC.RAI S.K.DUBEY Laboratory of Algal Biology Centre of Advanced Study in Botany Banaras Hindu University Varanasi-221005. India

The effects of chromium and tin on survival, growth, carbon fixation, nitrate reduction, ammonia assimilation, and nitrogenase activity of a N_2-fixing cyanobacterium, anabaena doliolum, and their amelioration by synthetic and natural complexans, viz., EDTA, nitrilotriacetic acid (NTA), pyridine dicarboxylic acid (PDA), and citrate, have been studied. Chromium proved to be much more toxic than tin, as it inhibited growth yield (49%), carbon fixation (53%), and nitrate reductase (79%), glutamine synthetase (30%), and nitrogenase activities (77%) at its sublethal concentration, whereas tin induced less inhibition of growth yield (42%), carbon fixation (50%). and nitrate reductase (66%), glutamine synthetase (32.4%), and nitrogenase activities (70%). Despite its inhibitory effects at 10μml^(-1), EDTA supplementation in metal-spiked medium counteracted the toxicity of chromium and tin more significantly than NTA, PDA, and citrate. When supplemented with LD_(50) of Cr, EDTA protected growth, carbon fixation, NR, GS. and Noase, respectively, by 32.6, 50.0, 33.3. 17.7. and 65.4%. However, EDTA-induced restoration of the above parameters at a sublethal concentration of tin was only 30.2, 50.0,28.1, 27.7, and 61.5%, respectively. Although NTA and citrate at 10/μgml^(-1) each were stimulatory to various processes of test cyanobacterium, they were comparatively less effective than EDTA in the amelioration of metal toxicity. On the basis of these observations, a generalized hierarchical sequence of protective efficiency of synthetic and natural cornplexing ligands may be given as EDTA > NTA > citrate > PDA. It seems plausible that the toxicity of various heavy metals may be regulated by a large array of organic complexing agents of the aquatic environment because they possess various metal binding sites. (c) 1989 Academic Press,lnc.

关键词： NTA anabaena doliolum Protective Effects of Certain Natural and Synthetic Complexans on the Toxicity of Chromium and Tin to a N2-Fixing Cyanobacterium PDA EDTA 络合试剂 Cr

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