Identification and Characterization of Zinc Solubilizing Bacteria Isolated from Mixed Sewage of East Kolkata Wetlands

The eastern wetlands of Kolkata have been reservoirs of some of the most unique metal tolerant bacteria that have inexplicable bioremediation potentialities in immobilizing radionuclides and toxic metals, in the degradation of oil, as a bioleaching agent, and in chelating zinc in living systems. Four bacterial strains were isolated from mixed sewage and designated as L4(1), L4(2), L4(3) and L4(4). Gram staining was performed to determine the Gram nature and morphology of the strains. All were found to be Gram negative coccobacilli in character. The IMViC biochemical tests were performed for the characterization of the strains. Further, the L4(4) strain was found to grow on Eosin Methylene Blue agar medium, thereby indicating it to be of coliform origin. Different concentrations of zinc solutions i.e., 100ppm, 500ppm and 1000 ppm were prepared in which each of the four strains were inoculated, and incubated at 37°C for 4 days. The bacterial growth was measured spectrophotometrically at 610nm. Atomic absorption spectroscopy analysis was performed to determine the uptake of zinc from the medium. Maximum uptake at 1000 ppm concentration of zinc was observed by strain L4(4) [954.7 mg/L] and least by strain L4(1) [896mg/L]. At 500ppm concentration of zinc, maximum uptake was observed by the strain L4(3) [464.7mg/L], and minimum by the strain L4(4) [442.7mg/L]. L4(4) was identified to be Escherichia coli. L4(3) having maximum uptake at 500ppm concentration was identified with the help of 16S rDNA analysis and was found to be Pseudomonas pseudoalcaligenes. This organism on one hand acts as a potential source of zinc to fishes thereby acting as a probiotic. We project this organism for future treatment of marine oil spills, and it can be considered as one stop remedy for different kinds of marine pollution.