Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/34369
Title: A STUDY OF MICROBIAL DEBROMINATION OF POLYBROMINATED DIPHENYL ETHERS AND SYNTROPHIC PRODUCTION OF HYDROGEN BY DEHALOCOCCOIDES SPECIES.
Authors: LEE LIP KIM
Keywords: Polybrominated diphenyl ether, PBDE, Bioremediation, Debromination, Detoxification, Dehalococcoides
Issue Date: 17-Aug-2011
Source: LEE LIP KIM (2011-08-17). A STUDY OF MICROBIAL DEBROMINATION OF POLYBROMINATED DIPHENYL ETHERS AND SYNTROPHIC PRODUCTION OF HYDROGEN BY DEHALOCOCCOIDES SPECIES.. ScholarBank@NUS Repository.
Abstract: Polybrominated diphenyl ethers (PBDEs) are highly toxic, persistent and bioaccumulative environmental pollutants that are commonly found in the environment and various biota. It is therefore important to find approaches to break down these compounds into non toxic or at least, less toxic components. Bioremediation is regarded as a promising approach because it is safe and natural, cost-effective and can be performed in-situ as opposed to conventional remediation methods, which merely contain/concentrate these hazardous substances. This drives the need for the discovery of novel microorganisms capable of efficient and rapid dehalogenation of PBDEs, in order to achieve the goal of detoxification of these harmful chemicals. To achieve the overall goal, a microcosm study was conducted to assess the ability of anaerobic microoganisms in soil and sediments from 28 locations in the United States of America, China and Singapore to debrominate the technical octabromodiphenyl ether (octa-BDE). Substantial debromination occurred within 2 months, resulting in the generation of hexa- through mono- BDEs, with the toxic tetra-BDEs as the most abundant debromination product (50% of total products). This investigation provides preliminary evidence that PBDE debrominating microbes are widespread across various regions and they produce highly toxic penta- and tetra- BDEs as the predominant debromination end products. The results also demonstrate, for the first time, debromination of the octa-BDE mixture in the absence of the relatively more readily utilizable electron acceptor (e.g., TCE or primer compounds), thus suggesting that microbial-mediated PBDE debromination may occur more easily in the natural environment than previously thought. The microcosm screening resulted in the discovery of cultures with novel PBDE debromination capabilities, among which, one microcosm (GY-T-2) was found to generate diphenyl ether as the debromination end product, demonstrating the ability of anaerobes to transform highly toxic PBDEs to safer, less toxic end products. Further investigations and enrichment of GY-T-2 led to a highly enriched coculture which completely debrominated the most toxic and prevalent PBDEs (congener 47, 99 & 100) to its non-brominated form, diphenyl ether. 16S rRNA based molecular methods revealed that the coculture consisted of Dehalococcoides and Desulfovibrio sp. and that debromination of PBDE was coupled to the growth of Dehalococcoides. This study represents the first demonstration of complete removal of bromines from congeners 47, 99, and 100 to its non-brominated form, a crucial step for the detoxification of PBDEs since diphenyl ether possesses much lower toxicity than PBDEs. Apart from microcosm GY-T-2, further investigations on another microcosm, C-T-7, resulted in the isolation of a novel Dehalococcoides strain capable of utilizing brominated compound 2,4,6-tribromophenol as metabolic electron acceptors. The new isolate, designated as IS, was also found to syntrophically oxidize acetate to produce hydrogen for both itself and its syntrophic partner under hydrogen limiting conditions. The reconstruction of syntrophic consortia with pure cultures in this study has provided new insights on the poorly understood interspecies and intraspecies interactions of members of the Dehalococcoides genus. Overall, the investigation on the ability of soil microorganisms to debrominate PBDEs has shown that biotic processes, specifically anaerobic microbial debromination, could contribute to the detoxification of these notorious pollutants in nature, thus shedding light on the restoration of PBDE-contaminated environments via microorganisms.
URI: http://scholarbank.nus.edu.sg/handle/10635/34369
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