EFFECT OF ARSENIC TOXICITY IN THE RICE FIELD CYANOBACTERIUM CALOTHRIXMeenakshi Banerjee, Jhumur Banik and Shaswati Bhattacharya
Heavy metals are inevitably common components of industrial wastes. One such metal which has attracted great attention lately is Arsenic because of the wide spread havoc to public health it has caused in West Bengal, Bangladesh and Tripura, caused by ground water contamination. It is a threat to the growth of the cyanobacteria in the rice fields which are natural biofertilizers for this crop.The present work is an attempt to study the effect of Arsenic (Na-Arsenate) on growth and nitrate reductase activity of the cyanobacterium Colothrix isolated from such a rice field in Calcutta. A comparison has been made with a local isolate of the same species of Colothrix. pH-7 was found to be optimal for the growth of Colothrix in both control and supplemented with 2.5% arsenic (As) which was the sub-lethal dose. pH-8 was found to be optimum fr,r thP local isolate and 2.5% was lethal for its growth. Sublethal dose was I%.An outstanding observation was very high nitrate reductase activity with 2.5% arsenic (As) addition in the strain from Calcutta and its reverse in the local isolate.The different light qualities did not have any significant effect on growth and nitrate reductase activity of Colothrix of both isolates. Presence of phosphate in culture greatly reduced arsenic toxicity in both the isolates suggesting that P and arsenic (As) probably compete for permease sites for cell entry. From environment point of view arsenic leaching into the rice fields does not appear to be very deleterious and phosphate management can reduce toxicity to a great extent.
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