Catabolic and genetic diversity of degradative bacteria from fuel-hydrocarbon contaminated aquifers

Subsurface sediments were recovered from two aquifers contaminated with pet roleum hydrocarbons in order to isolate and characterize indigenous microor ganisms capable of biodegrading fuel-related compounds. These sediments had been previously studied using catabolic gene probes providing putative dem onstration of significant biodegradation potential. Based on 16S rDNA seque nce analysis, the isolates were phylogenetically similar to common soil mic roorganisms, including members of the genera Pseudomonas Ralstonia, Burkhol deria, Sphingomonas, Flavobacterium, and Bacillus. A total of 26 isolates w ere obtained using a vapor-plate enrichment technique with the volatile aro matic hydrocarbons toluene, ethylbenzene, p-xylene, naphthalene, and JP-4 j et fuel. JP-4, toluene, and ethylbenzene served as growth substrates for mo re than 80% of the isolates, while less than 10% of the organisms grew on t he aromatic compounds benzene and o-xylene. Subsequent assays monitoring th e evolution of (CO2)-C-14, indicated that only seven isolates were able to completely mineralize target compounds. One isolate, designated CAFB-naph-5 , was able to completely mineralize the monoaromatic compounds salicylate a nd toluene, as well as the polyaromatic compound naphthalene. Molecular pro bing of the isolates showed four isolates hybridized with DNA probes target ing genes commonly associated with hydrocarbon-degrading bacteria. The isol ates also demonstrated broad ability to grow in the presence of the antimic robial agents streptomycin, tetracycline rifampicin, carbenicillin, nalidix ic acid, kanamycin, and ampicillin. The results of the study demonstrate th e biochemical and biodegradative capabilities of microorganisms isolated fr om contaminated aquifer systems and provide closure for indirect molecular monitoring of degradative potential in contaminated environments.