Isolation and Characterization of Engine Oil-Degrading Bacteria from Contaminated Soil at Garage Centers in Mekelle

Abstract

The release of engine oil by Mekelle mechanical workshops causes significant environmental pollution; bioremediation is an effective cleanup strategy. This study investigates the isolation and characterization of engine oil-degrading bacteria from contaminated soil at garage centers in Mekelle. Soil and water samples from ten garage centers in Mekelle were collected and analyzed for physicochemical properties. Bacteria were isolated using serial dilution and identified by morphological and biochemical characteristics. To assess the oil degradation ability, bacterial isolates were cultured on Bushnell-Haas agar with engine oil and incubated at 37°C for 14 days. Moreover, the isolates were evaluated for biosurfactant production, heavy metals and salt tolerance, antibiotic susceptibility, as well as for compatibility. Results showed the pH level of the soil ranging from 4.7 ± 0.2 to 6.6 ± 0.2, with temperatures between 25 ± 3.27°C and 34 ± 0.0°C. The isolates were identified as Pseudomonas aeruginosa, Bacillus cereus, Staphylococcus aureus, Acinetobacter baumannii, Bacillus pumilus, and Bacillus megaterium. B. pumilus (98.9 ± 91.6%) showed the highest oil degradation rate in soil followed by A. baumannii (98.7 ± 80%). Whereas, B. megaterium (96.9 ± 92.8%), B. cereus (96.7 ± 88.2%), and P. aeruginosa (96.5 ± 84.6%) showed the highest biodegradation rate in water. However, B. megaterium (98.9 ± 88.8%) achieved a high degradation rate in media. The highest biosurfactant was produced by P. aeruginosa, A. baumannii, and B. cereus. S. aureus and A. baumannii exhibit broad tolerance to all tested heavy metals. P. aeruginosa, B. megaterium, B. cereus, and B. pumilus exhibit significant salt tolerance. Moreover, the antibiotic sensitivity testing reveals that P. aeruginosa, A. baumannii, and B. megaterium are promising candidates for bioremediation due to their susceptibility to effective antibiotics, while strains like B. cereus, S. aureus, and B. pumilus exhibit intermediate as well as multidrug resistance, necessitating careful antibiotic selection. So, from the results obtained, bacterial isolates could be the most effective for the bioremediation of oil spills.