Ding Chang, Rogers Matthew J, Yang Kun-Lin, He Jianzhong
Department of Civil and Environmental Engineering, National University of Singapore, Singapore, 117576, Singapore.
Department of Chemical and Biomolecular Engineering, National University of Singapore, Singapore, 117576, Singapore.
Environ Microbiol. 2017 Jul;19(7):2906-2915. doi: 10.1111/1462-2920.13817. Epub 2017 Jul 7.
Polybrominated diphenyl ethers (PBDEs), chemicals commonly used as flame-retardants in consumer products, are emerging persistent organic pollutants that are ubiquitous in the environment. In this study, we report a PBDE-respiring isolate - Dehalococcoides mccartyi strain GY50, which debrominates the most toxic tetra- and penta-BDE congeners (∼1.4 µM) to diphenyl ether within 12 days with hydrogen as the electron donor. The complete genome sequence revealed 26 reductive dehalogenase homologous genes (rdhAs), among which three genes (pbrA1, pbrA2 and pbrA3) were highly expressed during PBDE debromination. After 10 transfers of GY50 with trichloroethene or 2,4,6-trichlorophenol as the electron acceptor instead of PBDEs, the ssrA-specific genome island (ssrA-GI) containing pbrA1 and pbrA2 was deleted from the genome of strain GY50, leading to two variants (strain GY52 with trichloroethene, strain GY55 with 2,4,6-trichlorophenol) with identically impaired debromination capabilities (debromination of penta-/tetra-BDEs ceased at di-BDE 15). Through analysis of Illumina paired-end sequencing data, we identified read pairs that probably came from variants that contain ssrA-GI deletions, indicating their possible presence in the original strain GY50 culture. The two variant strains provide real-time examples on rapid evolution of organohalide-respiring organisms. As PBDE-respiring organisms, GY50-like strains may serve as key players in detoxifying PBDEs in contaminated environments.
多溴二苯醚（PBDEs）是一类常用于消费品阻燃剂的化学物质，是环境中普遍存在的新型持久性有机污染物。在本研究中，我们报告了一株以PBDEs为呼吸底物的菌株——脱卤球菌属麦氏菌株GY50，该菌株能以氢气作为电子供体，在12天内将毒性最强的四溴和五溴二苯醚同系物（约1.4 μM）脱溴生成二苯醚。完整的基因组序列显示有26个还原性脱卤酶同源基因（rdhAs），其中三个基因（pbrA1、pbrA2和pbrA3）在PBDEs脱溴过程中高表达。用三氯乙烯或2,4,6 - 三氯苯酚作为电子受体而非PBDEs对GY50进行10次传代培养后，含有pbrA1和pbrA2的ssrA特异性基因组岛（ssrA - GI）从菌株GY50的基因组中缺失，产生了两个变体（以三氯乙烯为电子受体的菌株GY52和以2,4,6 - 三氯苯酚为电子受体的菌株GY55），它们的脱溴能力均受到同等程度的损害（五溴/四溴二苯醚脱溴在二溴二苯醚15时停止）。通过对Illumina双端测序数据的分析，我们鉴定出可能来自含有ssrA - GI缺失变体的读段对，表明它们可能存在于原始菌株GY50培养物中。这两个变体菌株为有机卤呼吸生物的快速进化提供了实时实例。作为以PBDEs为呼吸底物的生物，类似GY50的菌株可能是受污染环境中PBDEs解毒的关键参与者。
