Mercury and lead tolerance in hypersaline sulfate-reducing bacteria
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Sulfate-reducing bacteria (SRB) HSR 1, HSR 4, and HSR 14 isolated from the salt pans of Goa, India grew best at 90-100 ppt salinity on substrates like formate, acetate, lactate, butyrate, ethanol and benzoate. They were gram negative, non-sporulating, non-motile rods lacking in desulfoviridin and cytochromes. Examination of these isolates for heavy metal tolerance and response studies in terms of growth and sulfate-reducing activity (SRA) were carried out using HgCl sub(2) and Pb(NO sub(3)) sub(2) at final concentration of 50, 100, and 200 and 100, 200 and 500 mu g ml sup(-1) respectively. With Hg, HSR 1 showed approx. 80% of the control's growth at 100 and 200 mu g ml sup(-1) but SRA reached only 60% of the control values at the end of 14 days. HSR 14 could reach is greater than 100% of the control's growth at 200 mu g ml sup(-1) but the SRA reached only up to 60% of the control without metal at 100 mu g ml sup(-1). Though the concentration of Pb was double that of Hg, HSR4 could grow and respire better than the control, the growth being stimulated by 160% and respiration by 170% in the presence of 500 mu g ml sup(-1) of Pb (NO sub(3)) sub(2). It is probable that some hypersaline SRB are more tolerant to heavy metals than the mesohaline counterparts and could be more effectively used for precipitating these metals in bioremediatory measures. Further examination of their responses to varied concentration of metals under different salinities would indicate their range of applicability.
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