Rice fields of Meghalaya especially in the coal mining belt receive water contaminated by effluents from mines that are known to carry harmful heavy metal ions such as Cu, Fe, Zn, Ni, Cd, As, Pb, Cr, etc. Cd exposure was analyzed in the cyanobacterium Nostoc muscorum Meg 1 isolated from a contaminated rice field in Sohra, Meghalaya, India. Toxicity study established 0.5 ppm on day 3 to be the LD 50 . At LD 50 chlorophyll a and total protein concentration was reduced by 50.9 and 52.5%, while nitrogenase and glutamine synthetase activities were inhibited by 40.8 and 38.4%. EDX and FTIR analyses confirmed Cd binding and participation of hydroxyl, carbonyl, carboxyl and phosphate groups in biosorption of Cd onto the cell surfaces. SEM study established morphological changes. At pH 8.0 and temperature 25 ± 2°C, the cyanobacterium removed 92% Cd within 24 h. Of this, 91% Cd was adsorbed on the cell surface while 4% was internally accumulated. The energy required for internal accumulation of Cd was partly provided in the form of ATP synthesized during active photosynthesis. The Langmuir isotherm was found best fitted with a R 2 value 0.98 when compared to Freundlich and Temkin adsorption isotherms. The maximum sorption capacity, Q max, of the organism was 71.4 mg of Cd per g of biomass. R L value of 0.29 indicated favorable interaction between cyanobacterial biomass and Cd. The adsorption intensity, n value 7.69 g/L obtained from Freundlich isotherm showed that the organism possessed high Cd sorption capacity.
Nostoc muscorum was isolated from a coal mining pit in Chiehruphi, Meghalaya, India, and its potential to remove Zn(II) and Cu(II) from media and the various biochemical alterations it undergoes during metal stress were studied. Metal uptake measured as a function of the ions removed by N. muscorum from media supplemented independently with 20 μmol/L ZnSO4 and CuSO4 established the ability of this cyanobacterium to remove 66% of Zn(2+) and 71% of Cu(2+) within 24 h of contact time. Metal binding on the cell surface was found to be the primary mode of uptake, followed by internalization. Within 7 days of contact, Zn(2+) and Cu(2+) mediated dissimilar effects on the organism. For instance, although chlorophyll a synthesis was increased by 12% in Zn(2+)-treated cells, it was reduced by 26% in Cu(2+)-treated cells. Total protein content remained unaltered in Zn(2+)-supplemented medium; however, a 15% reduction was noticed upon Cu(2+) exposure. Copper enhanced both photosynthesis and respiration by 15% and 19%, respectively; in contrast, photosynthesis was unchanged and respiration dropped by 11% upon Zn(2+) treatment. Inoculum age also influenced metal removal ability. Experiments in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (a photosynthetic inhibitor), carbonyl cyanide m-chlorophenyl hydrazone (an uncoupler), and exogenous ATP established that metal uptake was energy dependent, and photosynthesis contributed significantly towards the energy pool required to mediate metal removals.
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