Characterization of Heavy Metal-Tolerant Bacteria from Dumpsites in Katsina Metropolis and their Bioremediation Potential

Abstract

Heavy metals have harmful effects on living organisms, microorganisms, and the environment as a whole. There is a lack of studies on heavy metal-tolerant bacteria from dumpsites in Katsina Metropolis, despite their potential for application in heavy metal bio-removal. Therefore, this study was conducted to characterize heavy metal-tolerant bacteria from refuse dump sites in Katsina Metropolis, with the goal of assessing their potential for bioremediation of heavy metal contamination. Soil samples were collected from four dumpsites: A, B, C, and D. Bacteria were isolated using serial dilutions and plating techniques. These isolates were then Gram-stained and underwent various biochemical tests, including indole, catalase, citrate, motility, starch hydrolysis, strings (exopolysaccharide), urease, and oxidase tests. Heavy metal tolerance was assessed by culturing the bacteria in minimal salt medium supplemented with various metal types at different concentrations: zinc, cobalt, nickel, lead, and chromium. The metal salts used were ZnSO₄, NiSO₄, Pb(NO₃)₂, CoCl₂, and K₂Cr₂O₇. Molecular identification of metal-tolerant isolates was identified through 16S rRNA gene sequencing. The concentration of heavy metal salts in the soil samples ranged from 0.058 to 0.42 (chromium), 0.341 to 0.952 (zinc), 0.17 to 1.54 (lead), 0.001 to 0.04 (cobalt), and 0.037 to 0.103 (nickel) ppm. The highest bacterial count was 9.8 × 10¹³ CFU/g in sample A, which also had the highest zinc concentration (0.952 ppm). Isolates A1 and B1 showed high chromium tolerance at lower concentrations. Molecular identification revealed Bacillus sonorensis, Achromobacter mucicolens, Bacillus licheniformis, and Lysinibacillus composti as the dominant metal-tolerant species. This study provides the first characterization of heavy metal-tolerant bacteria from dumpsites in Katsina Metropolis, identifying novel strains with bioremediation potential.