| Aerobic polycyclic aromatic hydrocarbon (PAH) degradative pathways have been described in a wide variety of bacteria, fungi and algae. The occurrence and role of these pathways and their corresponding genes in natural attenuation in environmental systems remain poorly understood. The primary goal of this dissertation research was to determine the concentration and frequency of five degradative genes within natural microbial communities exposed to ambient, low and high levels of PAHs using a quantitative-competitive PCR approach adapted for microbial ecology use. PAH concentrations, total microbial biomass and microbial community structure for sediment samples were also determined using a coupled biochemical approach. Community structure analysis indicated that microeukaryotes may be indirectly responding to the contamination, suggesting the development of a PAH-based food web within the microbial communities.; Gene frequencies and concentrations reflected increases with elevated levels of contamination. However, the measured frequencies for most genes indicated that only 0.1% or less of the microbial community had the genetic capacity to degrade the contaminants using described aerobic pathways and their corresponding genes and suggested these sequences are rare in these environmental samples. Metabolic assays indicated that the detected genetic capacity was sufficient to account for the overall biodegradative potential observed within the entire sediment microbial community. These data support that, although the reported frequencies were lower than those others have described, the determined frequencies are indicative of the genetic capacity of natural populations in these sediments. While it is likely that additional unidentified degradative pathways and genes exist and are operating in the environment, the data presented in this dissertation support that many of the well understood enzymes and pathways, while primarily studied and defined within laboratory settings, catalyze the majority of the metabolic activity observed in this environmental setting. |
