EVALUATION OF THE EFFICIENCY OF A BACTERIAL CONSORTIUM IN DEGRADING POLYCYCLIC AROMATIC HYDROCARBONS UNDER THE INFLUENCE OF AND WITHOUT COPPER METAL STRESS

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants found extensively in petroleum-contaminated environments. They pose a severe risk due to their carcinogenic, mutagenic, and bio-accumulative properties. This study investigates the ability of a certain selected bacterial consortium to degrade PAHs, specifically naphthalene and phenanthrene, under nutrient-limited conditions and copper stress as the heavy metal. Primary bacterial isolates obtained from environmental samples were screened on Bacto Bushnell-Haas agar infused with PAHs as the sole carbon source for primary screening. Effective colonies were then subjected to secondary screening using methylene blue as a redox indicator, and the absorbance was quantified through a spectrophotometric analysis at the absorbance level of 609nm. These methods include culturing bacterial colonies in Bushnell-Haas broth, with varying concentrations of PAHs and copper sulphate (20 ppm, 40 ppm, 60 ppm, 80 ppm, and 100 ppm). Absorbance reading indicated effective PAH degradation, particularly at 20 ppm, 40 ppm, and 80 ppm for phenanthrene and 20 ppm and 60 ppm for naphthalene. Triplicate experiments ensured statistical reliability. Initial confirmation of bacterial strains M11, C1, G13, M20, and J6 was carried out using Gram staining. The confirmed isolates were then subjected to antagonistic assays, which verified their mutual compatibility and diversity for effective consortium-based PAH degradation. Bacterial strains survived nutrient starvation and utilized naphthalene and phenanthrene as sole carbon sources. Primary screening identified efficient colonies, which were further evaluated through secondary screening using absorbance-based measurements. After 7 days, a phenanthrene-treated sample without copper showed a decrease in absorbance from 0.295 to 0.122, indicating 69.13% degradation. Under copper-induced stress, the consortium remained metabolically active, though with slightly reduced degradation.The isolates retained metabolic activity even under copper-induced stress, specifically at a concentration of 81.32 mg/kg of Cu, confirming their tolerance and resilience in heavy metal-contaminated environments, making them strong strains for an eco-friendly environment, contributing to advancing microbial bioremediation technologies and providing insights into PAH biodegradation under dual-stress conditions. This research highlights the potential applications of bacterial consortia in bioremediation targeting PAH contamination in metal-stressed environments.