Microbial community changes during the bioremediation of creosote-contaminated soil

Abstract

To investigate the effects of aeration on the ex situ biodegradation of polycyclic aromatic hydrocarbons (PAHs) in creosote-contaminated soil and its effect on the microbial community present. Aerated and nonaerated microcosms of soil excavated from a former timber treatment yard were maintained and sampled for PAH concentration and microbial community changes by terminal restriction fragment length polymorphism (TRFLP) analysis. After an experimental period of just 13 days, degradation was observed with all the PAHs monitored. Abiotic controls showed no loss of PAH. Results unexpectedly showed greater loss of the higher molecular weight PAHs in the nonaerated control. This may have been due to the soil excavation causing initial decompaction and aeration and the resulting changes caused in the microbial community composition, indicated by TRFLP analysis showing several ribotypes greatly increasing in relative abundance. Similar changes in both microcosms were observed but with several possible key differences. The species of micro-organisms putatively identified included Bacilli, pseudomonad, aeromonad, Vibrio and Clostridia species. Excavation of the contaminated soil leads to decompaction, aeration and increased nutrient availability, which in turn allow microbial biodegradation of the PAHs and a change in the microbial community structure. Understanding the changes occurring in the microbial community during biodegradation of all PAHs is essential for the development of improved site remediation protocols. TRFLP allows useful monitoring of the total microbial community.