Metabolism of PAHs and methyl-substituted PAHs by Sphingomonas paucimobilis strain EPA 505

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 3-methyl-methylfluoranthene, 7-methlybenz[a]anthracene, 5-methylchrysene, and their corresponding unsubstituted parent hydrocarbons was investigated. The rate of degradation of 3-methylfluoranthene, 7-methylbenz[a]anthracene, and 5-methylchrysene by a resting cell suspension of S. paucimobilis grown on fluoranthene was 20.4, 6.2, and 2.7 nmole/mg of wet cells/hr, respectively. The rate of degradation of fluoranthene, benz[a]anthracene, and chrysene was 10.7, 3.4, and 1.4 nmole/mg of wet cells/hr, indicating that methylated PAHs are degraded at a higher rate than the corresponding unsubstituted analogs. Two major isolated metabolites of benz[a]anthracene were identified as 2-hydroxy-3-naphthoic acid, and 2-hydroxy-3-phenanthroic acid. Unlike benz[a]anthracene, 7-methylbenz[a]anthracene was metabolized to its cis-1,2-diol to a significant extent by S. paucimobilis suggesting that the presence of a methyl group at position 7 of benz[a]anthracene hinders the action of the enzymes (presumably dehydrogenases), which convert cis-1,2-diol to the corresponding catechol.