Microbial Debromination of Polybrominated Diphenyl Ethers by Dehalococcoides-Containing Enrichment Culture.

Siyan Zhao,Yide He,Siyan Fan,Yongjun Zhang

doi:10.3389/fmicb.2021.806795

Abstract

Polybrominated diphenyl ethers (PBDEs), commonly used as flame retardants in a wide variety of consumer products, are emerging persistent pollutants and ubiquitously distributed in the environment. The lack of proper bacterial populations to detoxify these recalcitrant pollutants, in particular of higher brominated congeners, has confounded the attempts to bioremediate PBDE-contaminated sites. In this study, we report a Dehalococcoides-containing enrichment culture, PB, which completely debrominates 0.44 μM tetra-brominated diphenyl ether (BDE) 47 to diphenyl ether within 25 days (0.07 μM Br–/day) and extensively debrominates 62.4 ± 4.5% of 0.34 μM hepta-BDE 183 (0.006 μM Br–/day) with a predominant generation of penta- through tri-BDEs as well as small amounts of diphenyl ether within 120 days. Later, a marked acceleration rate (0.021 μM Br–/day) and more extensive debromination (87.7 ± 2.1%) of 0.38 μM hepta-BDE 183 was observed in the presence of 0.44 μM tetra-BDE 47, which is achieved via the faster growth rate of responsible bacterial populations on lower BDE-47 and debromination by expressed BDE-47 reductive dehalogenases. Therefore, the PB enrichment culture can serve as a potential candidate for in situ PBDE bioremediation since both BDE-47 and BDE-183 are dominant and representative BDE congeners and often coexist in contaminated sites.

Highlights

Polybrominated diphenyl ethers (PBDEs) are a class of commonly used flame retardants and widely added in a variety of products, from construction materials, electrical and electronic equipment to household products and textiles
As anaerobic and anoxic benthic sediments and soils are major sinks and environmental reservoirs for PBDEs, anoxic dehalogenation by microorganisms becomes an important route for eliminating PBDEs in such an environment
Penta- through monoBDEs as well as diphenyl ether were produced as end products with an average decrease of bromine/diphenyl ether from 7 to 4.89 ± 0.37, with a 30.14 ± 5.3% removal of the total bromine

Summary

Introduction

Polybrominated diphenyl ethers (PBDEs) are a class of commonly used flame retardants and widely added in a variety of products, from construction materials, electrical and electronic equipment to household products and textiles Their toxicity and persistence have drawn great public concerns that the commercially manufactured PBDEs [deca-brominated diphenyl ether (BDE) mixture, octa-BDE mixture, and penta-BDE mixture] were listed as persistent organic pollutants by the Stockholm Convention, as well as their use were banned or gradually phasing out (UNEP, 2009). Compared with the lower BDE congeners (with 1–4 bromines), higher BDE congeners (with 5– 10 bromines) are usually of lower bioavailability and are more resistant to microbial degradation (Palm et al, 2002) Both microcosms established from a versatile environment and isolated microorganisms have shown slower and less extensive debromination on deca- through hexa-BDEs rather than pentaand tetra-BDEs (Lee and He, 2010). Cultures that can more efficiently debrominate PBDEs and further be applied in in situ warrant further exploration

Methods

Results

Conclusion