Characterization of fluoranthene- and pyrene-degrading bacteria isolated from PAH-contaminated soils and sediments

Sixteen environmental samples, from the United States, Germany and Norway, with histories of previous exposure to either creosote, diesel fuel or coal tar materials, were screened for bacteria which could degrade high molecul ar weight (HMW) polycyclic aromatic hydrocarbons (PAHs). A modified version of the spray plate technique was used for the isolations. Using fluoranthe ne (FLA) and pyrene (PYR) as model HMW PAHs, we isolated 28 strains on FLA and 21 strains on PYR. FLA degraders were defined as able to grow on FLA bu t not PYR. PYR degraders grew on both PAHs. All PYR degraders were found to be Gram-positive and all FLA degraders were Gram-negative. GC-FAME analysi s showed that many of the PYR degraders were Mycobacterium spp and many of the FLA degraders were Sphingomonas spp. Comparison of the metabolic charac teristics of the strains using the spray plate technique and direct growth studies revealed that more than half of the FLA degraders (59%) were able t o cometabolize PYR (ie, they produced clearing zones or colored metabolites on spray plates but did not grow on the PAH) and the ability of many of th ese strains to cometabolize fluorene, anthracene, benzo[b]fluorene, benzo[a ]anthracene and benzo[a]pyrene was significantly affected by pre-exposure t o phenanthrene. Studies on the metabolic products produced from PYR cometab olism by strain EPA 505 suggested the possibility of attack at two differen t sites on the PYR molecule. However, the inability to derive degradable ca rbon from initial opening of one of the PYR rings probably accounted for th e lack of growth on this PAH by the FLA-degrading strains. The PYR degrader s on the other hand, were less able to cometabolize HMW PAHs, even followin g pre-exposure to PHE. Characterization of the FLA degradation pathway for several of the Sphingomonas isolates indicated oxidation and ring opening t hrough to acenaphthenone as the principle metabolite. Strain CO6, however, also oxidized FLA through fluorenone, suggesting a dual attack on the FLA m olecule, similar to that observed by others in Mycobacterium spp.