Degradation of polycyclic aromatic hydrocarbons dissolved in Tween 80 surfactant solutions bySphingomonas paucimobilisEPA 505

The degradation rates of mixtures of pyrene (PYR), fluoranthene (FLA), and phenanthrene (PHE) by Sphingomonas paucimobilis EPA 505 were measured in the presence of the nonionic surfactant Tween 80. For strain EPA 505, FLA and PHE are growth substrates, while PYR is not. Linear degradation rates ranging from 0.05 to 2.2 mg·L–1·h–1were observed for FLA, PYR, and PHE at approximately 107colony-forming units (CFU)/mL. At lower biomass, PYR degradation exhibited lognormal degradation. The degradation rates of PYR, FLA, and PHE increased with increasing biomass and substrate concentration. At high FLA concentrations, FLA degradation rates were faster in the presence of surfactant than in the absence of surfactant, suggesting that some of the FLA was transported directly into the cell from the micellar phase. In mixtures, PHE was the preferred substrate and was utilized first, followed by FLA and then PYR. Once the competing substrates were degraded, the remaining substrate was degraded at the same rate or faster than the rate found in the single-substrate system. Based on the results with Tween 80, it appears that PHE, PYR, and FLA are competing for the same enzymatic sites.Key words: PAH mixtures, microbial degradation, surfactant, solubilization, EPA 505.