9H-Carbazole and its derivatives are useful for versatile pharmacological applications. To obtain different derivatives of 9H-carbazole, 24 isolates of biphenyl-utilizing bacteria have been investigated regarding their ability to produce hydroxylated 9H-carbazole metabolites. Our analyses showed that 9H-carbazole was primarily converted into 9H-carbazol-1-ol (15 strains) and 9H-carbazol-3-ol (9 strains), while carbazol-9-ol was formed as a minor product (12 strains). The formation of 9H-carbazol-3-ol by the spontaneous release from the corresponding dihydrodiols was provided by the first-time detection of 3-hydroxy-1,2,3,9-tetrahydrocarbazol-4-one. The dependence of product yields on different parameters was exemplarily analyzed for Ralstonia sp. SBUG 290. Biphenyl-grown cells showed higher oxidation activities than cells cultivated with organic acids or nutrient broth, while co-cultivation of Ralstonia sp. SBUG 290 with biphenyl and 9H-carbazole led to an enhanced yield of 9H-carbazol-1-ol. The tested bacterial strains were also studied regarding their biotransformation of the two structure-related compounds 9H-fluorene and dibenzothiophene. Twenty-one strains primarily transformed 9H-fluorene into 9H-fluoren-9-ol and fluoren-9-one. Three strains accumulated benzo[c]chromen-6-one as a novel dead-end product during the incubation with 9H-fluorene, 9H-fluoren-9-ol, and fluoren-9-one. Dibenzothiophene has been mainly transformed into the dead-end product dibenzothiophene-5-oxide, while additional metabolites indicated that the transformation followed the so called Kodama pathway.

Different 9H-carbazole derivatives have been investigated within the last decades due to their broad range of pharmacological applications. While the metabolism of 9H-carbazole has previously been reported, nothing was known about the bacterial transformation of 2,3,4,9-tetrahydro-1H-carbazole and 9-methyl-9H-carbazole. Thus, for the first time, the bacterial biotransformation of 2,3,4,9-tetrahydro-1H-carbazole and 9-methyl-9H-carbazole was analyzed using biphenyl-grown cells of Ralstonia sp. strain SBUG 290 expressing biphenyl 2,3-dioxygenase. This strain accumulated 3-hydroxy-1,2,3,5,6,7,8,9-octahydrocarbazol-4-one and 6'-iminobicyclohexylidene-2',4'-dien-2-one as major products during the incubation with 2,3,4,9-tetrahydro-1H-carbazole. Carbazol-9-yl-methanol was verified as the primary oxidation product of 9-methyl-9H-carbazole. In addition, 9H-carbazol-1-ol, 9H-carbazol-3-ol, and 3-hydroxy-1,2,3,9-tetrahydrocarbazol-4-one where detected in lower concentrations during the transformation of carbazol-9-yl-methanol and 9-methyl-9H-carbazole. Products were identified by high-performance liquid chromatography, gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, as well as (1)H and (13)C nuclear magnetic resonance analyses.