Assessment of rhizosphere bacterial community diversity in polycyclic aromatic hydrocarbon contaminated soil

Phytoremediation is defined as the clean-up of contaminated soil and water using green plants. This innovative remediation approach has been used for many impacted sites to remove contaminants while simultaneously restoring ecological resources at relatively low cost. Polycyclic aromatic hydrocarbons (PAH) are ubiquitous contaminants and some are known carcinogens. Due to the significant amount of land contaminated with these carcinogenic compounds, they are of concern. For this dissertation research project, phytoremediation of PAH contaminated soil was assessed by monitoring PAH concentration, as well as changes in the bacterial community structure, over a time period of 10 months using tall fescue (Festuca arundinacea). Enhanced degradation of PAH was observed, with a maximum reduction in pyrene at a rate 36% higher than that noted for the unvegetated control. The dissipation of \u3c 4 ring PAH, 4 ring PAH, and \u3e 4 ring PAH in unvegetated soil was 70%, 54%, and 49% respectively, while a higher dissipation rate was observed in tall fescue treated soil of 78%, 68%, and 61% at the end of 10 months. A higher degradation rate of 4 ring and \u3e 4 ring PAH in the tall fescue treatment suggests that plants can promote rhizosphere degradation of the more recalcitrant PAHs in soil. Microbial enumeration results showed greater total bacterial numbers and PAH degrading bacteria in rhizosphere soil when compared to non-vegetated soil. The results from the terminal restriction fragment length polymorphism (T-RFLP) analysis indicated that there was a shift in the rhizosphere bacterial community during the phytoremediation process