Isolation, screening, and characterization of heavy metal-resistant bacteria from solid waste dumping sites in Central Gondar, Northwest, Ethiopia.

Abstract

Objective: Heavy metal pollution is one of the more recent problems of environmental degradation caused by rapid industrialization and human activity. The objective of this study was to isolate, screen, and characterize heavy metal-resistant bacteria from solid waste disposal sites.

Methods: In this study, a total of 18 soil samples were randomly selected from mechanical sites, metal workshops, and agricultural land that received wastewater irrigation. Isolation and screening of the isolates were based on multiple heavy metal (copper (Cu), chromium (Cr), and lead (Pb)) resistance potential. Morphological, biochemical, and 16S rRNA gene sequencing techniques were used to identify the isolates. The minimum inhibitory concentration (MIC) of the potential isolates was further examined at various concentrations (3, 6, 12, 25, 50, and 100 µg/mL). Each isolate's ability to biodegrade and resist antibiotics was also examined.

Results: About 21 bacterial isolates were obtained. Among these, six potential isolates (Agri10^-2Is2, Agri10^-3Is2, Agri10^-3Is1, AL10^-1Is2, AL10^-3Is1, and GA10^-2Is1) were selected. The isolates displayed varied colony morphologies and biochemical characterization features. Phylogenetic tree results revealed that Agri10^-2Is2, Agri10^-3Is2, Agri10^-3Is1, AL10^-1Is2, AL10^-3Is1, and GA10^-2Is1 were identified as Bacillus subtilis, Bacillus subtilis, Bacillus species, Bacillus tequilensis, Klebiesella species, and Cronobacter sakazakii, respectively. Every isolate gave a different MIC value. The biodegradation capacity of Agri10^-2Is2, Agri10^-3Is2, Agri10^-3Is1, AL10^-1Is2, AL10^-3Is1, and GA10^-2Is1 was 92.2%, 92.57%, 92.37%, 92.66%, 92.85%, and 92.52% against Cu; 95.07%, 94.07%, 93.07%, 93.4%, 91.4%, and 94.4% on Cr; and 95.51%, 94.53%, 95.62%, 96.87%, 94.86%, and 97.09% against Pb, respectively. All isolates were found to be resistant to the tested antibiotics.

Conclusion: This study concludes that the selected bacterial isolates could be potential agents for bioremediation of heavy metal-polluted environments.