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Investigation of Zn and Cu toxicity on bacteria isolated from soil and seawater

Niolaki Maria

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Summary

Industrialization has improved the human living conditions however it has caused severe pollution problems One of these negative impacts was heavy metal pollution. Heavy metals constitute a serious threat to the environment and public health mainly because of their long term exposure to the environment and their bioaccumulation. Most common heavy metals are the following: zinc, copper, lead, mercury, chromium, nickel and arsenic. These end up into the ground water and the soil either from rainfall or directly from disposal of unprocessed industrial waste. Besides scientific and technological progress all industrialization problems are yet to be resolved.An efficient bioremediation strategy for the resoration of polluted areas requires specific environmental microorganisms that are resistant to high concentrations of heavy metals.The main objective of the present study was to isolate environmental bacteria and to assess their ability to remove Zn and Cu from aquatic samples.Firstly, bacteria were isolated form soil and seawater and the interaction between them and heavy metals was studied. Secondly the resistant bacterial isolates were tested for their efficiency to remove Zn and Cu from seawater samples.Bacteria strains were isolated from seawater and soil from various areas of Chania region. Heavy metals used were in the form of salts, zinc sulphate (ZnSO4.7H2O) and copper sulphate (CuSO4.5H2O). The concentration range, that was examined, for the Zinc was from 1.5 mg/L to 200mg/L and for the Copper was from 0.01 mg/L to 1,25mg/L.The resistance of microorganisms was tested based on the Minimum Inhibitory Concentration (MIC60). For that purpose the microdilution method was applied to nutrient broth (Broth Microdillution), based on the CLSI protocol (Clinical and Laboratory Standards Institute).Among metals examined, it was observed that copper is more toxic than zinc, therefore bacteria appeared to exhibit higher resistance against Zinc. As copper causes a reduction of most bacteria population of the minimum concentration examined.Specifically, toxic concentration (MIC60) of Zinc for most bacteria, isolated from seawater, varied from 100 mg/Lto 150 mg/L while Cu concentration varied from 0.04 mg/L to 0.62 mg/L.For bacteria isolated from soil, it was found that toxic concentration (MIC60) of Zinc varied from 50 mg/L to 75 mg/L while Cu concentration varied from 0.01 mg/L to 0.04 mg/L.During bioremediation experiments seawater samples were spiked with the metals of our interest and subsequently, were inoculated with the resistant bacterial strains. The metal concentration was measured applying the ICP-MS method. It was observed that bacteria were highly effective for Zinc removal (higher than 82% Zinc removal). On the other hand, Copper removal was not tested because bacteria at acclimation stage in this metal displayed slow growth but also a decrease in their population after seven (7) days of incubation.

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