Citrobacter sp. Y3 Harboring a Novel Gene HBCD-hd-1 Mineralizes Hexabromocyclododecane (HBCD) with New Metabolic Pathways Based on Multi-omics Characterization

Background: Hexabromocyclododecane (HBCD) is a typical persistent organic pollutant that is widely detected in the environment. Until now, a microorganism resource that can degrade and even completely mineralizing HBCD is lacking. Results: : By stable isotope analysis, we found that the Citrobacter sp . strain Y3 can use 13 C-HBCD as its sole carbon source and degrade or even mineralize it to 13 CO 2 with a maximum conversion rate of 100% in approximately 14 days. Genomics, proteomics, and metabolomics were used to study the catabolic pathway of HBCD biodegradation by strain Y3. Several enzymes reportedly involved in the degradation of HBCD were identified in the strain Y3. A new functional gene named HBCD-hd-1 encoding a haloacid dehalogenase was cloned and heterologously expressed in Escherichia coli . The recombinant E. coli transformed the typical intermediate 4-bromobutyric acid (4-BBA) to 4-hydroxybutanoic acid (4-HDBA) and showed excellent degradation performance on HBCD with a degradation rate of 100% in only 2 days. Meanwhile, HBCD was well debrominated by the recombinant E. coli , because nearly 100% bromine ions were detected by ion chromatograph (IC) in vitro. Conclusion: This is the first report on the degradation function of haloacid dehalogenase in HBCD treatment. Strain Y3 can potentially degrade brominated flame retardants such as HBCD especially in a low-nutrient environment.