Assessment of the microbiological potential for the natural attenuation ofpetroleum hydrocarbons in a shallow aquifer system

A multidisciplinary field study investigating the fare and transport of pet roleum hydrocarbons commonly associated with jet-fuel contamination is curr ently underway at Columbus Air Force Base (AFB), Mississippi. Sixty sedimen t cores from 12 boreholes were recovered from the study aquifer. The goal o f this initial sampling was to characterize the potential microbial activit y using C-14-labeled substrates, as well as the presence, abundance, and di stribution of specific hydrocarbon degrading genotypes using DNA:DNA hybrid ization. Enumeration of total microbial abundance using a 16S rDNA universa l oligonucleotide probe was compared to traditional enumeration methods. To tal culturable populations determined by spread plate analysis ranged from a low of 10(4) to more than 10(6) organisms per gram sediment. Microbial ab undance estimated by DNA hybridization studies with 16S rDNA genes ranged f rom 10(7) to 10(8) organisms per gram sediment. Molecular analysis of aquif er samples using DNA probes targeting genes encoding the degradative enzyme s alkane hydroxylase (alkB), catechol 2,3-dioxygenase (nahH), naphthalene d ioxygenase (nahA), toluene dioxygenase (todC1C2), toluene monooxygenase (to mA), and xylene monooxygenase (xylA), as well as two probes measuring metha nogenic microorganisms, codh (carbon monoxide dehydrogenase) and mcr (methy l coenzyme reductase), revealed that each target gene sequence was present in nearly all 60 samples. The presence of organisms demonstrating the pheno type to degrade BTEX and naphthalene was further supported using mineraliza tion assays with C-14-labeled benzene, toluene, naphthalene, and phenanthre ne. Minimal activity occurred during the first 24 hours. After a period of 5-7 days, greater than 40% of the target compounds were mineralized in aqui fer sediments.