The innate resources of water and land are polluted by hydrocarbons, heavy metals, and other organic/inorganic compounds, and pollutants have become a significant concern because of their persistent and hydrophobic nature in the environment. In this study, two effective biosurfactant-producing indigenous bacterial strains, Bacillus subtilis strain R6 and Paenibacillus dendritiformis strain S2, were selected based on screening tests. First, we targeted the biodegradation of crude oil (C9-C30 9 -C 30 hydrocarbons) by the bacterial strains in a mineral salt medium under optimal conditions for 15 days. The results revealed that both strains obtained approximately 97 % degradation efficiency. Simultaneously, iron oxide nanoparticles with a size of 10 nm were green synthesized using Aerva lanata flower extract and confirmed with different spectroscopic and microscopic techniques. Furthermore, the bioremediation of soil co-contaminated with crude oil and heavy metals was performed using a mixed consortium of B. subtilis strain R6 and P. dendritiformis strain S2, iron oxide nanoparticles (1 and 2 g/kg), and a biosurfactant under optimal conditions. Toxicity assessments were performed by growing Vigna radiata in the bioremediated soil. Significant bioremediation efficiencies were observed in the biosurfactant and iron oxide nanoparticle-added systems, reaching a maximum efficiency of 99% in system VII. This integrated approach can be used for the practical treatment of co-contaminated environments.

This work was supported by the Science and Technology Innovation 2030 (2023ZD04062), National Key R&D Program of China (2022YFD1400300), Agricultural Science and Technology Innovation Program of Chinese Academy of Agricultural Sciences and China Agriculture Research System.Young Elite Scientists Sponsorship Program by CAST (2022QNRC001), the Youth Innovation Program of Chinese Academy of Agricultural Sciences (Y2023QC23) We acknowledge Nanotechnology Research Centre (NRC) and SRM Central Instrumentation Facility (SCIF), SRMIST for providing the instrumentation facilities. We acknowledge the Material Characterization Facility, Department of Physics and Nanotechnology, Collage of Engg. and Technology, SRMIST. The authors are grateful to the Department of Science and Technology, and Vellore Institute of Technology, Vellore for providing financial support to acquire " Inductively Coupled Plasma Mass Spectrometry (ICP-MS)" through "Promotion of University Research and Scientific Excellence (PURSE)" under Grant No.SR/PURSE/2020/34 (TPN 56960) and carry out the work. We would like to express our deepest gratitude to Dr. Narenkumar Jayaraman, National Postdoctoral Fellow for his unwavering support throughout this research, specifically for ICP-MS analysis which have greatly enriched this work. Also we acknowledge Department of Biotechnology, Faculty of Science and Humanities, SRMIST for providing lab facilities to carry out this research work.