Heavy metal tolerance in the psychrotolerant Cryptococcus sp. isolated from deep-sea sediments of the Central Indian Basin
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A deep-sea isolate of the psychrotolerant yeast Cryptococcus sp. (NIOCC#PY13) obtained from polymetallic nodule-bearing sediments of the Central Indian Basin was examined for its capacity to grow in the presence of various concentrations of the heavy metal salts i.e., ZnSO sub(4) , CuSO sub(4), Pb(CH sub(3) COO) sub(2) and CdCl sub(2). It demonstrated considerable growth in the presence of 100 mg/l concentrations of the above-mentioned four heavy metal salts both at 30 degrees C and 15 degrees C. This strain tolerated comparatively higher levels of these four metal salts than other deep-sea and terrestrial yeast isolates belonging to Cryptococcus, Rhodotorula, Rhodosporidium and Sporidiobolus spp. Optimum pH for growth of this isolate was in the range of 6-8 in the presence of heavy metal salts at these two temperatures. Scanning electron microscopic (SEM) studies exhibited altered cell surface morphology of the cells under the influence of heavy metals compared to that with control. The adsorption of heavy metals to the cells was demonstrated by FTIR and EDAX analysis. As evidenced by atomic absorption spectrophotometric (AAS) analysis, about 30-90 percent of the heavy metals were removed from the culture supernatant after 4 days of growth at 30 degrees C. This deep-sea yeast isolate appears to be a potential candidate for bioremediation of metal-contaminated sites. Moreover, its metal tolerance properties provide a significant insight into its ecological role and adaptations to growth in such extreme conditions.
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