Assessment of metal-reducing bacteria residing in industrial wastewater: a bacterial-based bioremediation approach

Abstract

Background: Metals are required in minor amounts in the human body to perform vital functions, but beyond that level, they become toxic and cause many harmful effects. At present, polluted water is a large source of these heavy metals inside our body. Bioremediation is one of best treatments for the removal of these heavy metals from water. Objectives: The main objective of the current study was to isolate metal-reducing bacteria from soil and wastewater samples from different industries. Furthermore, the metal reducing potential of the bacteria was also evaluated under various environmental conditions (pH, temperature, incubation time, and UV exposure). Methodology: Different bacterial strains were isolated that were resistant to different concentrations of zinc (Zn) and chromium (Cr) from wastewater and soil samples from four different industries (Riaz textile mills, Sitara chemical industry, Mandiali paper mills and Siddique leather works). Morphological characterization was carried out with the help of Gram staining, spore staining and motility tests. Biochemical tests were performed, such as catalase, oxidase, and H2S production tests, starch hydrolysis tests and Simon citrate tests. Chromium reduction after UV exposure was calculated to check mutation effects on chromium reduction. Results: A total of 14 bacterial strains were isolated from the soil and wastewater samples. Six strains were Zn resistant, while eight strains were chromium resistant. A total of five strains were isolated from wastewater out of fourteen strains, while the remaining nine strains were isolated from soil samples of these industries. The bacterial strains were rod-shaped cocci and coccobacillus. The growth of bacterial strains under different environmental conditions, such as temperature, pH and incubation time, was observed, and the best growth was found at 37◦C, pH 7.0 and after 48 hrs. Maximum reduction at different concentrations was observed at pH 7.0 and 37◦C and after 48 hrs. Conclusion: In conclusion, the bacterial strains isolated from industrial wastes and soils showed significant resistivity against various concentrations of Zn and Cr and reduced it efficiently under different conditions (pH, incubation time, temperature and UV light). The use of microorganisms for bioremediation is an environmentally friendly and cost-effective approach to reduce heavy metals present in our water and soil.