Biodegradation of Carbazole byPseudomonasspp. CA06 and CA10

Abstract

Two bacterial strains, CA06 and CA10, that assimilate carbazole (CAR) as the sole source of carbon and nitrogen were isolated from 202 farm soil samples and 4 activated sludge samples, and identified as Pseudomonas spp. Growth conditions for strains CA06 and CA10 on CAR were examined. Anthranilic acid (AN) and catechol (CAT) were identified as the main metabolites of CAR by high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS). When strains CA06 and CA10 were cultivated in a medium containing 17mM CAR, 1.4mM AN, and 0.1 mM CAT were accumulated in the culture broth, but AN disappeared after 140 h of incubation. An initial oxidation product, 2ʹ -aminobiphenyl-2,3-diol, and a meta-cleavage product, 2-hydroxy-6-oxo-6-(2ʹ -aminophenyl)hexa-2,4-dienoic acid, were tentatively identified in the culture broth of CAR by GC-MS. When AN was used for a substrate in culture by these strains, CAT and a small amount of cis, cis-muconate was detected by HPLC. This conversion suggested the existence of an ortho-c1eavage. The activities of the meta-cleavage enzymes for bipheny-2,3-diol (the initial oxidation intermediate analog of 2ʹ -aminobiphenyl-2,3-diol), 3-methylcatechol, and CAT were measured using the crude cell extracts of CAR- and AN-grown cells. The meta-cleavage enzymes of two strains for biphenyl-2,3-diol was induced during the growth on CAR, but not induced by AN. Based on these results, a CAR degradation pathway is proposed.