Tetrachloroethene and 3-chlorobenzoate dechlorination activities are co-induced in Desulfomonile tiedjei DCB-1

Desulfomonile tiedjei, a strict anaerobe capable of reductively dechlorinating 3-chlorobenzoate, also dechlorinates tetrachloroethene and trichloroethene. It is not known, however, if the aryl and aliphatic dechlorination activities are catalyzed by the same enzymatic system. Cultures induced for 3-chlorobenzoate activity dechlorinated tetrachloroethene and trichloroethene to lower chlorinated products while uninduced parallel cultures did not dechlorinate either substrate. The observed rate of PCE dechlorination in induced cultures was 22 #tool h-1 g protein -1, which is considerably faster than previous rates obtained with defined cultures of this organism. These results show that both dechlorination activities are co-induced and therefore, that the dechlorination mechanisms may share at least some components. Abbreviations: P C E tetrachloroethene, T C E trichloroethene, cis-DCE cis-dichloroethene, trans-DCEtrans-dichloroethene, 3FBz 3-fluorobenzoate, 3C1Bz 3-chlorobenzoate Contamination of groundwater by chlorinated aliphatic hydrocarbons has led to concern over their environmental fate. Many of these compounds, including tetrachloroethene (PCE), are anaerobically dechlorinated in the natural environment and by both methanogenic and sulfate reducing enrichment cultures (for reviews see McCarty 1988; Vogel et al. 1987). The anaerobic dechlorination of PCE is of special interest since, unlike trichloroethene (TCE) and lower substituted ethenes, PCE is apparently not attacked by aerobic microorganisms. Little is known, however, about either the bacteria responsible for the anaerobic dechlorination of PCE or the molecular mechanism involved in the reaction. Desulfomonile tiedjei strain DCB-1 was originally isolated from an anaerobic enrichment growing on 3chlorobenzoate (Shelton & Tiedje 1984). D. tiedjei, a sulfate reducing bacterium (DeWeerd et al. 1990), can obtaining energy by using 3-chlorobenzoate as an alternate electron acceptor, producing benzoate and HC1 as products (Dolfing 1990; Dolfing & Tiedje 1987; Mohn & Tiedje 1990). Interestingly, D. tiedjei also dechlorinates PCE. In one study, D. tiedjei gave the highest rate ofPCE dechlorination among several pure cultures of anaerobes tested (Fathepure et al. 1987). The slow growth rates and yields of D. tiedjei under the medium conditions used previously made studies of the relationship between these two dechlorination activities difficult. Medium improvements leading to increased growth rates and our own studies on induction of 3-chlorobenzoate dechlorination activity have led us to examine whether these two activities may be related. Specifcally, does PCE dechlorination activity co-induce with 3-chlorobenzoate dechlorination activity. For these experiments we induced 3-chlorobenzoate dechlorination activity with 3-fluorobenzoate, an effi-