A strain of Pseudomonas putida was isolated that transforms dibenzothiophene (DBT) to DBT sulfone (DBT-5-dioxide) via DBT-5-oxide. It also degrades DBT to 3-hydroxy-2-formyl benzothiophene via an alternate and previously described pathway, and to an unidentified red crystalline compound. Neither DBT sulfone nor 3-hydroxy-2-formyl benzothiophene are further degraded by this organism.Key words: dibenzothiophene, microbial degradation, Pseudomonas, dibenzothiophene sulfone, sulfur metabolism.