A carbazole-utilizing bacterium was isolated by enrichment from petroleum-contaminated soil. The isolate,designated Sphingomonas sp. strain XLDN2-5, could utilize carbazole (CA) as the sole source of carbon,nitrogen, and energy. Washed cells of strain XLDN2-5 were shown to be capable of degrading dibenzofuran(DBF) and dibenzothiophene (DBT). Examination of metabolites suggested that XLDN2-5 degraded DBF to2-hydroxy-6-(2-hydroxyphenyl)-6-oxo-2,4-hexadienic acid and subsequently to salicylic acid through the angulardioxygenation pathway. In contrast to DBF, strain XLDN2-5 could transform DBT through the ringcleavage and sulfoxidation pathways. Sphingomonas sp. strain XLDN2-5 could cometabolically degrade DBFand DBT in the growing system using CA as a substrate. After 40 h of incubation, 90% of DBT was transformed,and CA and DBF were completely removed. These results suggested that strain XLDN2-5 might be useful inthe bioremediation of environments contaminated by these compounds.