Isolation and Characterization of Phyllosphere Bacteria and their Bioremediation-Potential of Spent Engine Oil Contaminated Soil

Environmental pollution from spent engine oil (SEO) is a growing concern due to its persistence and toxicity risks to soil health and ecosystems, necessitating the continuous search for sustainable and cost-effective bioremediation approaches. This study investigated the potential of phyllosphere bacteria for bioremediation of SEO-contaminated soils. Leaves were purposively sampled from ten mechanic workshops in Katsina, Nigeria, to isolate and identify native bacteria using morphological characteristics and analysis with the VITEK 2 Compact kit. For hydrocarbon degradation studies, isolates were cultured on mineral salts medium (MSM) containing SEO as the sole carbon source. To validate the SEO remediation potential, a 60-day simulated soil microcosm experiment was conducted by mixing SEO-contaminated soil with bacterial inoculums (10 mL of broth culture containing 1010CFU/mL cells) in six planting bags (four with individual bacterial isolates, one with bacterial consortium, and one as a control), and the soil recovery was monitored by measuring the physicochemical parameters, including pH, organic carbon, nitrogen content, and electrical conductivity. The main SEO degraders identified were Pseudomonas aeruginosa, Kocuria kristinae, and Pseudomonas oleovorans, with Pseudomonas aeruginosa and Kocuria kristinae having the highest growth rates (>22.4×107 CFU/mL) in SEO. Post-treatment analysis revealed significant improvements (p < 0.05) in soil quality/fertility, with the soil treated with bacterial consortia having the highest fertility level, showing an 11% increase in organic carbon, a 20% rise in nitrogen content, and stabilization of pH levels and improved electrical conductivity (an indicator of soil salinity), confirming reduction in pollutant levels. These findings showcase the promising role of phyllosphere bacteria in restoring SEO-polluted soils using a sustainable, cost-effective, and eco-friendly solution. Hence, this study provides a foundation for further research into mountable SEO bioremediation strategies, particularly in regions with limited access to advanced remediation technologies.