Abstract
The isolation of bacteria resistant to heavy metals is a topic of interest in the field bioremediation of contaminated water, soil and sediments. We report here the isolation of bacteria that is resistant to high concentration of a mixture of heavy metals namely cadmium, cupper, lead and zinc. The bacterial isolate was obtained from a site receiving heavy metal waste from the iron and steal factory; a major factory located in El-tebeen, south Helwan. The isolate was identified as Vibrio alginolyticus using the API system. The maximum tolerable concentration was 2.5 mM, 4 mM, 2.5 mM and 3.5 mM for cadmium, copper, lead and zinc respectively. Transmission electron micrograph of Vibrio alginolyticus grown in nutrient broth containing a mixture of the four tested heavy metals, showed bioaccumulation of heavy metal(s) on the bacterial cell wall. At the same time, there was an over all reduction in the concentration of heavy metals in culture supernatant; the percentage reduction was 20% for cadmium, 31% for cupper 40% for lead and 45%for zinc. The reduction occurred after 4 hrs incubation at 30°C for all metals, cupper, lead, and zinc while cadmium required 24 hrs incubation were required to achieve maximum reduction. This isolate could be used to accelerate the in situ bioremediation of sites contaminated by loads of mixed metals.
Highlights
Have been widely used to remove metal ions from industrial waste water
The mechanism by which microorganisms remove heavy metals can be divided into three categories; the first mechanism is the biosorption of metals ions on the cell surface, second intracellular uptake of metals ion and third chemical transformation of metal ions by microorganism (Pardo et al, 2003)
According to the standards permitted by the Ministry of Environmental Affairs in Egypt, the water sample obtained from wastes of Iron and Steal Factory contained above the permitted amounts of cadmium, lead and zinc
Summary
Have been widely used to remove metal ions from industrial waste water. Those methods are ineffective or expensive (Volesky, 1990). Biological methods such as biosorption and bioaccumulation provide promising alternative to chemical methods (Kapoor and Viraragharan, 1995). The mechanism by which microorganisms remove heavy metals can be divided into three categories; the first mechanism is the biosorption of metals ions on the cell surface, second intracellular uptake of metals ion and third chemical transformation of metal ions by microorganism (Pardo et al, 2003). Among the different technique employed for metals removal from multi elemental system, biosorption has been found to be highly selective (Knauer et al, 1997). The capacity of any biosorbent is mainly influenced by biomass characteristic, physiochemical properties of the target metals, and the micro environment of contact solution including pH, temperature and interaction with other ions
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