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novel bacterium, Dehalococcoides sp. strain MB, was recently discovered by research scientists in the ESE Department. This bacterium lives on the harmful organic solvents tetrachloroethene (PCE) and trichloroethene (TCE), which are released into the environment through their widespread use in metal degreasing or dry cleaning. The bacterium depends on PCE and TCE
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just like human beings depend on oxygen. The amazing microbe produces trans-1,2-dichloroethene, which is physiologically different from other strains of the same genus. Knowing how strain MB works will lead to better pollution cleanup strategies in the contaminated areas. As shown in Figure 1, the atomic force microscope (AFM) examination revealed homogeneous microbial morphology with a distinct disc shape and a diameter of 1000 nm, a maximum height of 97 nm, and a surface area of 1.96µm2.
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Figure 1: A
FM image of strain MB. |
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Although the novel PCE-to-trans-DCE dechlorinating strain MB is physiologically different from other members of the same genus, it shares 100% 16S rRNA gene sequence similarity with a PCE-to-vinyl chloride (VC) dechlorinating strain 195. DNA-DNA hybridization was performed on microarray chips built with probes to cover more than 99% of predicted protein-coding sequences of the strain 195 genome. Of the 1,579 probe sets on microarray, the genomic DNA of isolate MB hybridized to 1,404 (88.9%), suggesting that genes are highly conserved between strains MB and 195. In particular, among 19 reductive dehalogenase genes of strain 195, 10 genes were present in strain MB while 9 genes were designated absent due to the signal intensity criterion (Figure 2). Quantitative real-time PCR is currently used to detect the expression of functional reductive dehalogenase genes.
In summary, obtaining this new isolate could provide insightful information on the source of trans-DCE and increase our understanding on the diversity and specificity of the genus Dehalococcoides, which will contribute to the implementation of the bioremediation strategy. This study, for the first time, presents the application of microarrays to explore the genomic content of a trans-DCE producing isolate without sequencing the whole genome, thus adding to our knowledge on the evolution of this unusual microbial group - Dehalococcoides species.
This work was done in collaboration with current Ph.D student Dan Cheng.
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Dr Jianzhong He received her Ph.D. degree from the Georgia Institute of Technology in 2003. She was a postdoctoral researcher at the University of California at Berkeley for two years before joining the National University of Singapore as an Assistant Professor in 2005. Dr He’s research focuses on transformation and detoxification of environmental contaminants by novel microbes, converting waste to energy, environmental genetics and novel metabolism of microbes, and environmental application of genomics.
Email: jianzhong.he@nus.edu.sg |
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