Characterization and Identification of Some Indigenous Bacterial Strains for Heavy Metal Accumulation from Contaminated Soils

Numerous studies have reported elevated quantities of cadmium and nickel in soil, resulting in reduced plant growth, particularly in biomass, chlorophyll content, and photosynthetic traits due to their hazardous nature. Therefore, it is crucial to enhance plant resistance to heavy metal stress and reduce the toxicity of cadmium and nickel. In this study, several bacterial strains were isolated from heavy metal-contaminated soil to investigate their potential role in facilitating detrimental consequences of heavy metal stress. The capacity of the isolates to increase plant production under heavy metal stress and minimal inhibitory concentration was evaluated after the isolates were identified at the species level. Classic microbiological and molecular-genetic identification revealed that isolates #5, #18, and #11 were classified as Enterobacter cloacae Uz_5, Pseudomonas aeruginosa 18, and Enterobacter ludwigii 11Uz, respectively. P. aeruginosa 18 produced auxin in 4, 4.8, and 5.3 times greater than the control. In contrast, E.ludwigii 11Uz, Bacillus licheniformis 10, and Bacillus simplex 8 produced auxin equivalent to the control at various Cd cation amounts (2.4, 4.1, and 8.2 mg/l). During the 14th day of growth, at a Ni concentration of 191.4 mg/l, Enterobacter ludwigii 11 produced 81 mg/l of EPS, 1.2 times higher than the control. Bacillus atrophaeus 4 and Enterobacter ludwigii 11Uz produced 25-28 mg/l and 6.12 mg/l of EPS on days 7 and 14 of culture, respectively, at Cd2+ cation concentrations of 8.2 and 24.6 mg/l. These microorganisms demonstrate promising potential for bioremediation of heavy metal-polluted soils by reducing Ni2+ and Cd2+ toxicity and increasing the production of phytohormones and exopolysaccharides under heavy metal stress conditions.