Pyrene Biodegradation in Two Soils.

Pyrene is a polyaromatic hydrocarbon that exhibits variable biodegradation rates in soils. The objective of the laboratory incubation study was to determine the mineralization rate of ¹⁴C-labeled pyrene in two soils. A Captina silt loam and a Roxana loam were unamended or amended with 200 mg pyrene/kg soil and the four replications of each treatment were maintained at a moisture potential of -33 kPa and 24°C. The Captina and Roxana had initial pyrene degrader numbers of ≤2.70 and 3.78 log MPN/g, respectively. After 16 weeks, 2% of the ¹⁴C pyrene was recovered as ¹⁴CO₂ from the Captina soil. During the 16-week incubation, a 5-week acclimation period was observed followed by rapid biodegradation of pyrene resulting in 40% mineralization of the labeled pyrene in the Roxana soil. For the Captina soil, with or without pyrene addition, the respiration rate was 69 and 68 mg C-CO₂/100 g soil, respectively. For Roxana soil, with or without pyrene, the respiration rate was 21 and 13 mg C-CO₂/100 g soil, respectively. Pyrene biodegradation rates were determined by the number and activity of pyrene degrading microorganisms indigenous to the two soils. Real-time PCR and microarray assays are being developed to detect PAH degradative genes to assess the functional diversity of pyrene degradation in the two soils.