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首页> 外文期刊>Applied Microbiology >A New Catabolic Plasmid in Xanthobacter and Starkeya spp. from a 1,2-Dichloroethane-Contaminated Site
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A New Catabolic Plasmid in Xanthobacter and Starkeya spp. from a 1,2-Dichloroethane-Contaminated Site

机译：Xanthobacter和Starkeya spp中的新分解代谢质粒。从1,2-二氯乙烷污染的地点

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1,2-Dichloroethane (DCA) is a problematic xenobiotic groundwater pollutant. Bacteria are capable of biodegrading DCA, but the evolution of such bacteria is not well understood. In particular, the mechanisms by which bacteria acquire the key dehalogenase genes dhlA and dhlB have not been well defined. In this study, the genomic context of dhlA and dhlB was determined in three aerobic DCA-degrading bacteria ( Starkeya novella strain EL1, Xanthobacter autotrophicus strain EL4, and Xanthobacter flavus strain EL8) isolated from a groundwater treatment plant (GTP). A haloalkane dehalogenase gene ( dhlA ) identical to the canonical dhlA gene from Xanthobacter sp. strain GJ10 was present in all three isolates, and, in each case, the dhlA gene was carried on a variant of a 37-kb circular plasmid, which was named pDCA. Sequence analysis of the repA replication initiator gene indicated that pDCA was a member of the pTAR plasmid family, related to catabolic plasmids from the Alphaproteobacteria , which enable growth on aromatics, dimethylformamide, and tartrate. Genes for plasmid replication, mobilization, and stabilization were identified, along with two insertion sequences (IS Xa1 and IS Pme1 ) which were likely to have mobilized dhlA and dhlB and played a role in the evolution of aerobic DCA-degrading bacteria. Two haloacid dehalogenase genes ( dhlB1 and dhlB2 ) were detected in the GTP isolates; dhlB1 was most likely chromosomal and was similar to the canonical dhlB gene from strain GJ10, while dhlB2 was carried on pDCA and was not closely related to dhlB1 . Heterologous expression of the DhlB2 protein confirmed that this plasmid-borne dehalogenase was capable of chloroacetate dechlorination.IMPORTANCE Earlier studies on the DCA-degrading Xanthobacter sp. strain GJ10 indicated that the key dehalogenases dhlA and dhlB were carried on a 225-kb linear plasmid and on the chromosome, respectively. The present study has found a dramatically different gene organization in more recently isolated DCA-degrading Xanthobacter strains from Australia, in which a relatively small circular plasmid (pDCA) carries both dhlA and dhlB homologs. pDCA represents a true organochlorine-catabolic plasmid, first because its only obvious metabolic phenotype is dehalogenation of organochlorines, and second because acquisition of this plasmid provides both key enzymes required for carbon-chlorine bond cleavage. The discovery of the alternative haloacid dehalogenase dhlB2 in pDCA increases the known genetic diversity of bacterial chloroacetate-hydrolyzing enzymes.
机译：1,2-二氯乙烷（DCA）是有问题的异生物源地下水污染物。细菌能够生物降解DCA，但这种细菌的进化尚不十分清楚。特别是，细菌获得关键的脱卤酶基因dhlA和dhlB的机制尚未明确。在这项研究中，确定了从地下水处理厂（GTP）分离的三种降解DCA的需氧降解细菌（新奇菌Starellaa菌株EL1，自养黄腐Xanthobacter自营养菌菌株EL4和黄杆菌Xanthobacter flavus菌株EL8）的dhlA和dhlB的基因组背景。卤代烷脱卤酶基因（dhlA）与来自Xanthobacter sp。的规范dhlA基因相同。菌株GJ10存在于所有三种分离物中，并且在每种情况下，dhlA基因都携带在一个名为pDCA的37 kb环状质粒的变体中。 repA复制起始基因的序列分析表明，pDCA是pTAR质粒家族的成员，与来自Alphaproteobacteria的分解代谢质粒有关，能够在芳香族化合物，二甲基甲酰胺和酒石酸盐上生长。确定了用于质粒复制，动员和稳定化的基因，以及两个插入序列（IS Xa1和IS Pme1），它们很可能动员了dhlA和dhlB，并在需氧降解DCA的细菌的进化中发挥了作用。在GTP分离物中检测到两个卤代酸脱卤酶基因（dhlB1和dhlB2）。 dhlB1最有可能是染色体的，与菌株GJ10的经典dhlB基因相似，而dhlB2则携带在pDCA上，与dhlB1并不密切相关。 DhlB2蛋白的异源表达证实了该质粒携带的脱卤酶能够进行氯乙酸盐的脱氯反应。重要事项早期对DCA降解Xanthobacter sp。的研究。 GJ10菌株表明关键的脱卤酶dhlA和dhlB分别携带在225-kb线性质粒和染色体上。本研究已经在澳大利亚最近分离的降解DCA的Xanthobacter菌株中发现了显着不同的基因组织，其中相对较小的环状质粒（pDCA）携带dhlA和dhlB同源物。 pDCA代表了真正的有机氯-分解代谢质粒，首先是因为其唯一明显的代谢表型是有机氯的脱卤作用，其次是因为该质粒的获得提供了碳-氯键裂解所需的两种关键酶。在pDCA中发现另一种卤代酸脱卤酶dhlB2，增加了已知的细菌氯乙酸盐水解酶的遗传多样性。

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