P49: Determination of bacterial availability and toxicity of phenanthrene aged in soil using a specially reconstructed reporter strain

The location and toxicity of phenanthrene in soil according to aging time was visualized and quantified by two fluorescence-based reporter strains: strain D was constructed to generate green fluorescence and strain S was designed to die and thus to lose green fluorescence when the strain started to biodegrade phenanthrene. The relative fluorescence intensities of strain D and strain S increased and decreased linearly, respectively, as the concentration of freshly spiked phenanthrene increased up to 1,000 mg/kg in Ottawa sand and an organic matter-rich soil. After 18 months of aging, the relative fluorescence intensity rapidly decreased from 1.74±0.12 to 0.97±0.13 for strain D and increased from 0.64±0.03 to 1.08±0.13 for strain S in the organic matter-rich soil within 3 months, indicating that most of the phenanthrene in the soil became nonavailable to the reporter strains. In contrast, significant fluorescence changes were not observed in Ottawa sand, irrespective of aging time. Mathematical modeling also showed that more than 77% of the freshly spiked phenanthrene migrated into the inside of the soil during the aging period. The detection strategy employed in strain S (i.e., cell death in response to phenanthrene biodegradation, which resuting in declined fluorescence) was not previously reported in the literature, and the results were comparable to a widely used bacterial reporting system (e.g., strain D). Strain S may provide a promising tool to determine both bioavailable fraction and toxicity of phenanthrene in soil.