Heavy Metal Tolerance and Removal Efficiencies by Soil Bacterial Strains: Effects of Carbon and Nitrogen Sources

Several human activities contribute to the release of heavy metals into the environment, which constitutes a threat to the environment and human health; thus, there is a need for remediation of these metals.

The aim of this study was to evaluate the effects of carbon and nitrogen sources on tolerance to lead, nickel and cadmium by soil bacterial strains. The effects of carbon, nitrogen sources and carbon-nitrogen ratio on the bacteria strains were also explored. A total of ten bacterial species, which comprise Yersinia enterocolitica (1), Alcaligenes faecalis (4), Bacillus cereus (2), Enterobacter cloacae (1) and Bacillus subtilis (2), were identified. The screening was carried out in minimal media using different carbon sources (sodium acetate, glucose, sucrose and maltose), nitrogen sources (yeast extract, peptone, tryptone and potassium nitrate) and carbon/nitrogen (C/N) ratios (5:5, 5:4, 5:3 and 5:2). Based on tolerance index, the optimal carbon and nitrogen sources were observed to be sodium acetate and potassium nitrate, respectively, while the C/N ratio varied across the isolates.

At the end of the study, the tolerance index observed for cadmium, lead, and nickel ranged from 0.44 to 0.55, from 0.48 to 2.27 and from 0.19 to 1.95, respectively. Moreover, removal percentages that ranged from 12%-35%, 56%-97% and 79%-90% were observed for cadmium, lead and nickel, respectively, in the presence of the bacterial species.

The results showed the bacterial isolates' effectiveness in removing these heavy metals from the environment.