Degradation of polynuclear aromatic hydrocarbons by Sphingomonas paucimobilis

The ability of Sphingomonas paucimobilis, strain EPA 505 (a soil bacterium capable of utilizing fluoranthene as the sole source of carbon and energy for growth) to metabolize a variety of high molecular weight polynuclear aromatic hydrocarbons (PAHs) was investigated, After 16 h of incubation with 10 ppm of a PAH, a resting cell suspension (1 mg wet cells/ mt) of S. paocimobilis grown on fluoranthene degraded 80.0, 72.9, 31.5, 33.3, 12.5, and 7.8% of pyrene, benz[a]anthracene (B[a]A), chrysene, benzo[a]pyrene (B[a]P), benzo[b]fluoranthene (B[b]F), and dibenz[a,h]anthracene (DB[a,h]A), respectively. No degradation of dibenzo[a,l]pyrene was detected under these conditions. 1-Nitropyrene was degraded at a lower rate than pyrene. The extent of degradation of the PAHs increased with an increase in cell density. Studies with [7-C-14]B[a]P and [5,6,11,12-C-14]chrysene showed that, after 48 h of incubation, the cells degraded nearly 28 and 42% of [C-14]B[a]P and [C-14]chrysene to (CO2)-C-14, respectively, suggesting that the bacterium is able to metabolize B[a]P and chrysene via ring cleavage. No evolution of (CO2)-C-14 was defected from cultures incubated with [4,5,9,10-C-14]pyrene or [1,2,3,4,4a,4b-U-C-14]dibenz[a,l]pyrene. Analysis of the ethyl acetate extracts of the culture medium by reverse-phase HPLC showed that B[a], B[b]F, and B[a]A were each degraded to the major, high polar metabolite(s). The degradation of B[a]P with S. paucimobilis significantly reduced the mutagenic activity associated with the hydrocarbon. The addition of solubilizing agents such as Tween 80 or cyclodextrin to the incubation medium did not enhance the biodegradation of B[a]P by EPA 505. The addition of 5 ppm of B[a]A, chrysene, fluoranthene, or DB[a,h]A to the incubation medium containing 5 ppm of B[a]P had no effect on the degradation of B[a]P by EPA 505. However, the biodegradation of B[a]P was reduced by nearly 30% in the presence of 5 ppm of B[b]F. The results demonstrate that S. paucimobilis EPA 505 has the ability to degrade several four- and five-ring PAHs ranging in molecular size, shape, and chemical structure.