Microbial removal of zinc by a zinc resistant bacterium: potential in industrial waste remediation

Bioremediation, the use of living or dead microorganism to degrade or remove the waste, has been practised since humans first populated the world and had to dispose of their trash. Heavy metals can be extremely toxic as they damage organs and block functional groups of vital enzymes. Zinc is one of the most important heavy metals often found in effluents discharged and travels via bioaccumulation. The study was aimed in screening of zinc resistant/accumulator bacterial strains isolated from metal contaminated sites and determining the Zn (II) resistance/accumulation performance of selected bacterial strain as a new biosorbent. The maximum removal of Zn (II) at pH 7.0 was found to be 607 nmol/mg proteins at initial Zn (II) ion concentration of 1.0 mM and the Km value was 0.76mM. Competitive uptake experiments were performed with zinc in the presence of copper, cadmium, chromium, cobalt and nickel ions simultaneously and the zinc uptake was not much affected by these ions. Sensitivity of Zn (II) towards sodium azide, zinc cyanide 0.5% glucose and heat suggested that the process was metabolically inactive. The nature of the possible cell–metal ions interactions was evaluated by chemical and instrumental analysis including X-Ray diffraction and FTIR spectroscopy and revealed the involvement of cellular phosphate and carboxyl groups in zinc binding by the bacterial biomass. Almost 61% of biomass-bound Zn could be recovered using H2SO4 as the desorbing agent. In natural environment some bacterial strains develop resistance mechanisms that lead to the selection of metal resistant strains tolerating high zinc concentration.