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Dechloromonas aromatica RCB
   
   
 
 
  Dechloromonas aromatica strain RCB is the only organism in pure culture that can oxidize benzene in the absence of oxygen (5). It can also oxidize aromatics such as toluene, benzoate, and chlorobenzoate. D. aromatica couples growth and benzene oxidation to the reduction of either O2, chlorate, or nitrate (5). Benzene is completely mineralized to CO2. Benzene contamination is a significant problem worldwide. It is widely used in various manufacturing processes and is also a primary component of petroleum-based fuels. Benzene is a highly soluble, mobile, toxic, and stable hydrocarbon especially in ground and surface waters. It is poorly biodegraded in the absence of oxygen. The pathway of benzene degradation in D. aromatica is unknown, however, preliminary studies suggest that it has both a diooxygenase-based aerobic pathway and an as yet uncharacterized anaerobic pathway (5) (J.D. Coates, unpublished). The dioxygenase-based pathway is used by the organism when growing with O2 or chlorate as the electron acceptor. With chlorate as the electron acceptor, the oxygen required by the dioxygenase is supplied as a result of chlorite dismutation (J.D. Coates, unpublished). When anoxic aquatic sediments containing [14C]-labeled benzene were inoculated with D. aromatica, the benzene was rapidly oxidized to CO2 (R. Chakraborty, unpublished). These results demonstrate the applicability of D. aromatica to the engineered attenuation of benzene in-situ.

In summary, the Dechloromonas represents a unique genus with a broad range of novel metabolic capabilities and bioremediative applicability. Although this genus was only recently described (1), there are now several members in pure culture (1, 8). In addition, screening studies of a broad diversity of environments utilizing specific molecular probes (7) (L.A. Achenbach, unpublished) have demonstrated the ubiquity of this group of organisms. Although the role of Dechloromonas species in the environment has yet to be determined, as our studies indicate these organisms have a diverse range of metabolic capabilities to exploit. These unique metabolic capabilities foretell the likelihood of a significant number of novel genes, thus expanding the database for genomic and proteomic studies. Sequencing of the D. aromatica genome will greatly enhance our understanding of this unique group of organisms and thereby increase their applicability to bioremediation and biotechnology.

References

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  2. Achenbach, L. A. and J. D. Coates. 2000. Disparity between bacterial phylogeny and physiology. ASM News 66: 714-716
  3. Bruce, R.A., Achenbach, L.A., Coates, J.D. (1999). Reduction of (per)chlorate by a novel organism isolated from a paper mill waste. Environ Microbiol 1:319-331.
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  5. Coates, J.D., Chakraborty, R., Lack, J.G., O’Connor, S.M., Cole, K.A., Bender, K.S., and Achenbach, L.A. (2001) Anaerobic benzene oxidation coupled to nitrate reduction in pure culture by two novel organism. Nature 411: 1039-1043.
  6. Coates, J. D., R. A. Bruce and J. D. Haddock. 1998. Anoxic bioremediation of hydrocarbons. Nature 396:730.
  7. Coates, J. D., R. A. Bruce, J. A. Patrick and L. A. Achenbach. 1999. Hydrocarbon bioremediative potential of (per)chlorate-reducing bacteria. Bioremed J 3:323-334.
  8. Coates, J. D., U. Michaelidou, R. A. Bruce, S. M. O'Connor, J. N. Crespi and L. A. Achenbach. 1999. The ubiquity and diversity of dissimilatory (per)chlorate-reducing bacteria. Appl Environ Microbiol 65:5234-5241.
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  11. Michaelidou, U., Achenbach, L.A., and Coates, J.D. (2000). Isolation and characterization of two novel (per)chlorate-reducing bacteria from swine waste lagoons. In Perchlorate in the Environment (E. Urbansky, ed)
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