微生物转化六溴环十二烷研究进展

Microbial transformation of hexabromocyclododecanes: a review

六溴环十二烷(hexabromocyclododecanes,HBCDs)是一类包含多种异构体的阻燃剂,在环境中可随食物链积累,对人类和其他生物产生健康威胁.HBCDs可通过化学、物理和生物途径而被转化和降解,其中,微生物降解是清除HBCDs污染的重要途径.为提供生物修复HBCDs污染的理论依据,本文综述微生物转化HBCDs的研究进展.目前发现的HBCDs脱溴功能菌中,好氧菌株如Sphingobium chinhatense IP26和Pseudomonas sp. GJY可通过水解脱溴、消除溴化氢和还原脱溴途径将HBCDs转化为低溴化的醇类和(或)环烯烃;厌氧微生物如Dehalococcoides mccartyi 195通过还原脱溴途径将HBCDs转化为低溴化环烯烃. HBCDs在厌氧环境中降解较快,其原因与HBCDs在化学、物理和厌氧微生物转化过程中均可作为电子受体的性质相关.另一方面,由于HBCDs包含α-、β-和γ-HBCD等多种异构体,微生物转化HBCDs的过程普遍存在着立体、对映异构体选择性,这种选择性源于脱卤酶和异构体的空间结构之间的相互选择.微生物转化HBCDs存在的问题和未来的研究方向包括:功能菌与其脱卤酶的异构体选择性存在差异的原因;微生物转化带来的具有多种异构体的低溴化产物的生态毒理评价;将HBCDs高效降解菌应用于环境修复的过程中,菌群结构、功能基因、脱溴产物及其归趋等需深入探索;厌氧环境下HBCDs的降解更快,可作为HBCDs污染修复的一个切入点.

Hexabromocyclododecanes(HBCDs) are brominated flame retardants with α-, β-and γ-HBCD as the three dominant diastereisomers. HBCDs are listed in Annex A of the Stockholm Convention on Persistent Organic Pollutants(POPs). They pose a threat to the health of humans and other organisms because of their toxicity and biomagnification. HBCDs are generally enriched in soil and sediment and can be degraded via biotic and abiotic processes. Microbial degradation of HBCDs contributes to their transformation in the environment.More than ten bacterial strains with the ability to transform HBCDs have been characterized. Aerobic strains such as Sphingobium chinhatense IP26 and Pseudomonas spp. GJY transform HBCDs via hydrolytic debromination, HBr elimination, and reductive debromination pathways, yielding lower-brominated alkanols and alkenes such as pentabromocyclododecanol, tetrabromocyclododecadiol, tribromocyclododecatriol, and tetrabromocyclododecene. Anaerobic strains such as Dehalococcoides mccartyi 195 transform HBCDs through reductive debromination pathways, yielding lower-brominated alkenes such as tetrabromocyclododecene,dibromocyclododecadiene, and 1,5,9-cyclododecatriene. HBCDs can serve as electron acceptors in the reductive debromination pathway, which may be a reason why HBCDs are degraded faster in an anaerobic environment where they can accept electrons during chemical, physical, and microbial debromination.Microbial transformation of HBCDs is regio-and stereo-selective. This selection results from the structural characteristics of dehalogenase and HBCDs. The selective transformation of HBCDs in the environment leads to serious concerns regarding the toxicity of the various intermediates. Degradative strains have been used for bioremediation in the laboratory. However, the abundance of functional groups and genes, as well as the transfer of debrominated products, during bioaugmentation has not been well studied.