Biodegradation of dioxins by the endophytic bacterium Burkholderia cenocepacia 869T2: Role of 2-haloacid dehalogenase in dehalogenation

• Main Authors: Bao Anh Nguyen Thi, 阮氏寶英
• Other Authors: Huang Chieh-Chen
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/19522905829506304792

碩士 === 國立中興大學 === 生命科學系所 === 105 === Dioxin compounds are very toxic byproducts produced by combustion and industrial activities, thus their ubiquitous distribution and toxicity are worldwide concerns. Among of recent techniques, bioremediation is an environmental sustainable and cost-effective technology in detoxification of the environmental contaminants. In this study, a functional endophytic bacterium Burkholderia cenocepacia 869T2 was found to grow and effectively degraded TCDD compounds. According to transcriptomic analysis of B. cenocepacia 869T2, a number of dioxin-catabolic genes (aromatic-ring-hydroxylating dioxygenase, cytochrome P450, haloacid dehalogenase and others) involved to TCDD metabolism were detected with differential gene expressions at 6 and 12 hours. The initial hints and outline of dioxin degradation pathway were proposed for B. cenocepacia 869T2, and the transcriptome data indicated that the endophyte 869T2 was able to metabolize TCDD compounds from an early phase of growth. Among of detected dioxin-catabolic genes, haloacid dehalogenases (HADs) are responsible for dehalogentation which performs halogen removal from the carbon–halogen bond to detoxify halogenated compounds. Thus, with high up-regulations in response to TCDD, one of HADs (gene3580, Locus_tag: DT99_RS17940) was cloned by a vector pET24A(+) and expressed in E. coli BL21(DE3) to investigate its function for dehalogenation. The results had demonstrated that haloacid dehalogenase played a crucial role in dioxin dehalogenation by effectively releasing chloride ions from TCDD and a reduction of TCDD concentration. Through the evidences of whole transcriptome shotgun sequencing and HAD activity, haloacid dehalogenase has potentials to apply for dechlorination of other dioxin congeners and halogenated aromatic compounds. Further studies will be necessary to determine TCDD metabolic pathway and to have better understandings in TCDD degradative process.