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.
