Studies on biological dehalogenation of chlorinated organic compounds

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A strictly anaerobic bacterium Desulfitobacterium sp.Y51 converts tetrachloroethene (PCE) as a final electron acceptor to cis-1,2-dichloroethene (cis-DCE,) via trichloroethene (TCE) very efficiently. This reaction is associated with energy conservation and called as dehalorespiration or halorespiration. We obtained the following results.1.We purified a PCE-dehalogenase (PceA encoded by pceA), and raised polychlonal antibody against purified PceA. Using the antibody we found that PceA is localized at periplasm, associating the cell membrane.2.The production of PceA was highly inducible by addition of PCE or TCE. cis-DCE, on the other hand, inhibited the PceA production at the transcriptional level. The enzyme reaction was also inhibited by cis-DCE.3.We cloned additional genes upstream and downstream regions of pceAB gene cluster. The putatative regulatory pceR gene was found upstream of pceAB. PceR protein was bound with PCE and/or TCE and considered to stimulate the transcription of pceAB gene cluster.4.The commercial cis-DCE contained high amount of chloroform. About 6.6-kb DNA including pceAB genes were highly deleted (more than 80%) when the cells were grown with 1μM chloroform. The cell growth of wild type strain was greatly inhibited, but the growth of deletion mutant was not.5.We obtained a microbial consortium that dechlorinate PCE to ethylene completely in 10 days, in which Dehalococcoides strains, known as a completed dechlorination of various chlroethenes, were present.