Biosorption potential and plant growth promoting activities of zinc tolerant novel Chitinophaga niastensis HMR31 from zinc-infested zone

Heavy metal contamination in soil poses serious threats to agriculture, human health, and ecosystems. Bacterial biosorption has emerged as a sustainable, cost-effective, and eco-friendly approach for mitigating metal pollution. In this study, bacterial strain HMR31 was characterized through a polyphasic approach and evaluated for its ability to biosorb Zn(II), Fe(II), Pb(II), Cd(II), and Cr(III). Bacterial Zn accumulation was confirmed by AAS, SEM-EDX, and TEM analyses. The optimal pH, temperature, contact time, initial metal concentration, and biomass dose for heavy metal biosorption were determined. Phenotypic, chemotaxonomic (major fatty acids: iso-C15:0 and C16:1 5c; major hydroxy fatty acid: iso-C17:0 3-OH), and phylogenetic analyses of the 16 S rRNA gene identified the isolate as Chitinophaga niastensis HMR31. The biosorption efficiency followed the order Zn(II) > Fe(II) > Pb(II) > Cd(II) > Cr(III). Optimal biosorption was achieved at pH 7.0, 35 °C, 60 min contact time, 50 mg/L initial metal concentration, and 1.5 mg/mL biomass dose. The strain also exhibited multiple plant growth-promoting traits, including IAA, GA3, NH3, HCN, siderophore, ACC deaminase, and phosphate solubilization activity. In a pot experiment with Vigna radiata under zinc stress, inoculation with HMR31 alleviated toxicity and enhanced growth parameters. Thus, Chitinophaga niastensis HMR31 can be treated as a potential candidate for a concerted method in bioremediation to convert metal-contaminated sites to productive land.