Unravelling the biodegradation performance and mechanism of 3,6-dibromocarbazole by a novel strain Streptomyces sp. FW-32

Streptomyces sp. FW-32, an actinobacterial strain capable of degrading 3,6-dibromocarbazole (3,6-DBCZ), was isolated from polluted soils. >85 % of 3,6-DBCZ was degraded within 5 d under optimal conditions (glucose concentration of 5 g/L, pH of 7, initial 3,6-DBCZ concentration of 1 mg/L, temperature of 35 °C). The biodegradation of 3,6-DBCZ followed the first-order kinetic model with the degradation rate constant of 0.01713 h −1 . Biodegradation pathways of 3,6-DBCZ by Streptomyces sp. FW-32 were proposed, including debromination, oxidation, and aromatic ring cleavage. The intracellular enzymes of Streptomyces sp. FW-32, such as cytochrome P450, played an important role in 3,6-DBCZ biodegradation. In the earlier stage of 3,6-DBCZ biodegradation (1–2 d), the activities of SOD and CAT were enhanced by 3,6-DBCZ (≤10 mg/L), but 10 mg/L of 3,6-DBCZ inhibited the activities of these two antioxidant enzymes at the later period (4–6 days). Cell viability of strain FW-32 was stimulated by 3,6-DBCZ at 1 mg/L in the first two days of treatment, but it was suppressed by 10 mg/L of 3,6-DBCZ after 3 days of exposure. Strain FW-32 was able to efficiently degrade 3,6-DBCZ and its key intermediate carbazole in real river water. The results of this study illuminated the mechanism of 3,6-DBCZ biodegradation by a newly isolated strain FW-32 and indicated that strain FW-32 might be suitable for the elimination of 3,6-DBCZ from contaminated water. Overall, these findings were significant for developing microbial remediation to control 3,6-DBCZ pollution in water environments.