Aims: Our goal was to characterize a newly isolated strain of Mycobacterium austroafricanum, obtained from manufactured gas plant (MGP) site soil and designated GTI-23, with respect to its ability to degrade polycyclic aromatic hydrocarbons (PAHs). Methods and Results: GTI-23 is capable of growth on phenanthrene, fluoranthene, or pyrene as a sole source of carbon and energy; it also extensively mineralizes the latter two in liquid culture and is capable of extensive degradation of fluorene and benzo[a]pyrene, although this does not lead in either of these cases to mineralization. Supplementation of benzo [a]pyrene-containing cultures with phenanthrene had no significant effect on benzo[a]pyrene degradation; however, this process was substantially inhibited by the addition of pyrene. Extensive and rapid mineralization of pyrene by GTI-23 was also observed in pyrene-amended soil. Conclusions: Strain GTI-23 shows considerable ability to mineralize a range of polycyclic aromatic hydrocarbons, both in liquid and soil environments. In this regard, GTI-23 differs markedly from the type strain of Myco. austroafricanum (ATCC 33464); the latter isolate displayed no (or very limited) mineralization of any tested PAH (phenanthrene, fluoranthene or pyrene). When grown in liquid culture, GTI-23 was also found to be capable of growing on and mineralizing two aliphatic hydrocarbons (dodecane and hexadecane). Significance and Impact of the Study: These findings indicate that this isolate of Myco. austroafricanum may be useful for bioremediation of soils contaminated with complex mixtures of aromatic and aliphatic hydrocarbons.

We conducted a series of liquid-culture experiments to begin to evaluate the abilities of gaseous sources of nitrogen and phosphorus to support biodegradation of polycyclic aromatic hydrocarbons (PAHs). Nutrients examined included nitrous oxide, as well as triethylphosphate (TEP) and tributylphosphate (TBP). Cultures were established using the indigenous microbial populations from one manufactured gas plant (MGP) site and one crude oil-contaminated drilling field site. Mineralization of phenanthrene was measured under alternative nutrient regimes and was compared to that seen with ammoniacal nitrogen and PO 4 . Parallel cultures were used to assess removal of a suite of three-to five-ring PAHs. In summary, the abilities of the different communities to degrade PAH when supplemented with N 2 O, TEP, and TBP were highly variable. For example, in the MGP soil, organic P sources, especially TBP, supported a considerably higher degree of removal of low-molecular-weight PAHs than did PO 4 ; however, loss of high-molecular-weight compounds was impaired under these conditions. The disappearance of most PAHs was significantly less in the oil field soil when organophosphates were used. These results indicate that the utility of gaseous nutrients for PAH bioremediation in situ may be limited and will very likely have to be assessed on a case-by-case basis.

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Our laboratory is studying various forms and factors of chemically accelerated biotreatment (CAB) for hydrocarbons contaminated soils, i.e. polynuclear aromatic hydrocarbons; benzene, ethylbenzene, toluene, and xylenes (BTEX); and aliphatic moieties. As the biodegradation capacity of the contaminated soils is the decisive parameter in the CAB technology, we are investigating the effects of delivering nutrients (nitrogen and phosphorus moieties) to soils under simulated in-situ conditions to maximize biodegradation. Nitrogen and phosphorus containing compounds that are gases under expected field conditions are a major research area. In order to determine effectiveness of these additions it was necessary to first identify candidate soil that is suitably nutrient-limited. Slurry-phase bioreactors were the method to assess nutrient effects on contaminant degradation under "ideal" conditions, i.e. in systems where issues such as nutrient and contaminant bioavailability are minimized. In order to determine whether the Microtox  solid-phase test would be suitable for assessing the potential toxicity of the E&P soils to be used in remediation experiments and in determinations of environmentally acceptable endpoints, this assay was investigated. All procedures were followed according to manufacturer's instructions, and clean coarse sand (the same sand used to dilute the soil for column experiments) was used as a control. Solid-phase Microtox  analyses proved to be applicable to the experimental systems under study. In addition, soil moisture content (a w) was evaluated in both the nutrient study and the Microtox  evaluation.

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