EFFECT OF NICKEL STRESS ON ESCHERICHIA COLI AND SACCHAROMYCES CEREVISIAE
This study is carried out to understand the tolerance level of microbes to nickel ions. E. coli (prokaryote) and Saccharomyces cerevisiae (eukaryote) has been taken for the study. The Minimum inhibitory concentrations of NiSO4 for both the organisms were found to be 350 mg/L for E. coli and 3500 mg/L for S. cerevisiae. The growth of both of these organisms in different concentrations was studied. Generally, as the concentration of nickel sulphate in the media was increased, there was substantial decrease in growth of both the organisms. E. coli exhibited a delayed log phase at increasing concentrations of nickel sulphate whereas there was no such delayed log phase in the case of S. cerevisiae. In E. coli, at initial NiSO4 concentration of 50 mg/L, the percentage of ions remaining in the supernatant was 81% whereas it was 94% corresponding to 300 mg/L initial concentration of NiSO4. In S. cerevisiae, for initial NiSO4 concentration of 1000 mg/L, the percentage of Ni ions remaining in the supernatant was 82% whereas at 3000 mg/L of initial NiSO4 concentration, 98% Ni ions were remaining in the medium after 15 h. The amount of nickel ions removed from the medium at the end of 72 h was studied. In E. coli, the maximum removal at the end of 72 h was found to be around 33%. On the other hand, the maximum removal obtained in S. cerevisiae was around 77%. The cytosolic protein content was studied under nickel stress. In both the organisms, the high content of protein found corresponding to cultures treated with highest concentration of nickel sulphates. In E. coli, no significant difference was observed between the banding patterns of the control and treated samples except that far high molecular weight proteins were found to be over expressed in the nickel treated cultures. In S. cerevisiae, a protein corresponding to around 205 kDa was found to be down regulated in the 100 mg/L nickel sulphate treated culture. In addition, two new proteins corresponding to around 55 kDa and 80 kDa were overexpressed at higher concentrations of nickel sulphate.
MAHALAKSHMI T, ILAMATHI M, SIVA R AND T. B. SRIDHARAN
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