Changes in subsurface catabolic gene frequencies during natural attenuation of petroleum hydrocarbons

Subsurface hydrocarbon contamination associated with petroleum spills is a widespread occurrence that presents a significant threat to groundwater resources. The natural attenuation test site (NATS) at Columbus Air Force Base, MS, provided a unique opportunity to monitor changes in the molecular microbial ecology as well as stimulation of natural biodegradative processes under transient field study conditions. A large, synthetic jet fuel mixture containing BTEX compounds and naphthalene in a decane carrier was introduced into the subsurface. Over 462 days, a plume of hydrocarbon contamination developed and stabilized at a distance of less than 15 m downgradient from the source area. Exposure of indigenous microorganisms to the contaminant hydrocarbons was evaluated using an array of gene probes targeting common genotypes associated with the aerobic biodegradation of BTEX and naphthalene. Each of the targeted genotypes alkB, nahA, nahH, todC1C2, and xylA showed significant responses to hydrocarbon exposure. Aerobic mineralization potentials of selected contaminants were greater in sediments collected from within the plume relative to uncontaminated areas, suggesting that an aerobic contaminant-degrading community successfully developed within the plume. An increase in aerobic degradation activity coincided with the arrival of the hydrocarbon front within the well field. The Natural Attenuation Study at Columbus AFB successfully linked adaptations of indigenous microorganisms to hydrocarbon exposure during a transient field study.