Metal Resistant Bacteria from Tannery Effluent Discharged Soils: Isolation, Characterization and Application in Metal Bioremediation

Background: Pollution by metals is a serious environmental and health threat due to their high toxicity, and microbial bioremediation offers an eco-friendly strategy to restore contaminated soils. This study aimed to isolate and evaluate indigenous, metal tolerant bacteria from tannery effluent contaminated soils in the Ranipet belt for their potential in eco-friendly remediation and plant growth promotion. Materials and Methods: Five sandy loam soils from Ranipet tannery discharge sites showed saline-alkaline conditions, elevated Fe, Mn, Ni, Cr, Zn and Cu, and N/P enrichment with macronutrient imbalance. Fifteen distinct bacterial isolates were recovered; six grew at and tolerated up to 0.75 mM Cr and none at 1 mM, whereas all tolerated Pb²⁺ up to 0.5 mM and several remained viable at 4-7 mM, revealing markedly higher Pb than Cr tolerance and a subset of multi-metal-resistant strains. Results: The most tolerant Isolate (Is7) was identified by 16S rRNA sequencing as Stutzerimonas stutzeri and, in batch assays, removed 20.14% of Pb (1.41 mM from 7 mM) and 18.67% of Cr (0.14 mM from 0.75 mM), indicating moderate dual metal bioremediation capacity with scope for process optimization. Ecotoxicity tests with Eisenia fetida showed that S. stutzeri caused no adverse effects compared with a pathogenic Klebsiella pneumoniae control. Conclusion: Furthermore, a seed germination assay with green bean demonstrated an increase in germination from 60% (control) to 75% with S. stutzeri treatment, confirming its plant growth-promoting and non-phytotoxic nature. Overall, the indigenous Stutzerimonas stutzeri isolate from tannery impacted soil emerges as a promising, safe candidate for integrated bioremediation and biofertilization in metal contaminated agro ecosystems.