Assessing degradation of polycyclic aromatic hydrocarbons (PAHs) in front of tin (Sn) stress by a soil bacterial consortium

Polycyclic Aromatic Hydrocarbons (PAHs) are persistent in the environment and are toxic pollutants which have carcinogenic and mutagenic properties. They are composed of two or more fused benzene rings. Bacteria present in soil are capable of degrading these compounds via anaerobic and aerobic respiration. However, heavy metals such as tin have the ability to hinder the degradation capabilities of bacteria. The goal of this study is to isolate and identify soil bacteria capable of degrading Naphthalene and Phenanthrene in the presence of heavy metals. Soil samples were collected from 4 different locations in Sri Lanka: Colombo, Galle and Jaffna, as they are highly polluted areas according to previous literature and Meemure, as it had the lowest PAH pollution according to studies and were serially diluted and plated. Morphologically different strains were identified and starved on Bushnell Haas Agar. Primary screening was performed using Naphthalene and phenanthrene spiked plates. Five bacterial strains: RUSHJ08, RUSHC09, RUSHMO6, RUSHG02, and RUSHG04, were able to degrade these PAHs were identified and were a subjected to second screening using methyl blue. UV- Spectrophotometric analysis revealed that these bacteria can degrade over 40% of the PAHs under optimum conditions. RJO8 (Accession number PV942241) and RJO2 (Accession number PV942264) were identified as best PAH degraders. Gram staining was performed to identify Gram-negative and Gram-positive bacteria, and antagonistic assay was performed to identify the capability of the strains to exist as a consortium. Atomic Absorption Spectroscopy was performed to evaluate the presence of heavy metals in the Colombo soil sample, and the concentration of tin was 2.22mg/kg. The results of this experiment support the development of a bioremediation technique in tin-stressed environments, which provides a solution to environmentalpollution.