Two distinct enzyme systems are responsible for tetrachloroethene and chlorophenol reductive dehalogenation in Desulfitobacterium strain PCE1

Desulfitobacterium strain PCE1 is able to use tetrachloroethene and chloroa romatics as terminal electron acceptors for growth. Cell extracts of Desulf itobacterium strain PCE1 grown with tetrachloroethene as electron acceptor showed no dehalogenase activity with 3-chloro-4-hydroxyphenylacetate (Cl-OH -phenylacetate) and other ortho-chlorophenolic compounds in an in vitro ass ay. Extracts of cells that were grown with Cl-OH-phenylacetate as electron acceptor dechlorinated tetrachloroethene at 10% of the dechlorination rate of Cl-OH-phenylacetate. In both cell extracts dechlorination was inhibited by the addition of 1-iodopropane and dinitrogen oxide, inhibitors of cobala min-containing enzymes. The enzymes responsible for tetrachloroethene and C l-OH-phenylacetate dechlorination were partially purified. A 100-fold enric hed fraction of chlorophenol reductive dehalogenase was obtained that mainl y contained a protein with a subunit size of 48 kDa. The characteristics of this enzyme are similar to that of the chlorophenol reductive dehalogenase of D. dehalogenans. After partial purification of the tetrachloroethene re ductive dehalogenase, a fraction was obtained that also contained a 48-kDa protein, but the N-terminal sequence showed no similarity with that of the chlorophenol reductive dehalogenase sequence or with the N-terminal amino a cid sequence of tetra- and trichloroethene reductive dehalogenase of Desulf itobacterium strain TCE1 These results provide strong evidence that two dif ferent enzymes are responsible for tetrachloroethene and chlorophenol dechl orination in Desulfitobacterium strain PCE1. Furthermore, the characterizat ion of partially purified tetra-chloroethene reductive dehalogenase indicat ed that this enzyme is a novel type of reductive dehalogenase.