Reductive dehalogenation of brominated ethenes by Sulfurospirillum multivorans and Desulfitobacterium hafniense PCE-S Lidan Ye, 1 Anke Schilhabel, 1† Stefan Bartram, 2 Wilhelm Boland 2 and Gabriele Diekert 1 * 1 Department of Applied and Ecological Microbiology, Institute of Microbiology, Friedrich Schiller University, Philosophenweg 12, 07743 Jena, Germany. 2 Department of Bioorganic Chemistry, Max-Planck-Institute for Chemical Ecology, Hans-Knöll-Straße 8, 07745 Jena, Germany. Summary Sulfurospirillum multivorans and Desulfitobacterium hafniense PCE-S are anaerobes that can utilize tetra- chloroethene (PCE) as an electron acceptor in their energy metabolism. The end-product of PCE reduc- tion for both organisms is cis-1,2-dichloroethene, which is formed via trichloroethene as the intermedi- ate. The bacteria were able to dehalogenate cis- and trans-1,2-dibromoethene (cDBE and tDBE) in growing cultures and cell extracts. Dibromoethene supported growth of both organisms. The organisms debromi- nated cDBE and tDBE to vinyl bromide (VB); D. hafniense PCE-S also produced ethene in addition to VB. The PCE reductive dehalogenases (PCE deha- logenases) of S. multivorans and D. hafniense PCE-S mediated the debromination of tribromoethene (TBE) and both isomers of 1,2-DBE, indicating that this enzyme was responsible for the reductive dehaloge- nation of brominated ethenes. cDBE, tDBE, 1,1-DBE and VB were formed upon TBE debromination; VB was the major end-product. The PCE dehalogenase of D. hafniense PCE-S also formed ethene. With the puri- fied enzymes from both organisms the kinetic prop- erties of dehalogenation of brominated alkenes were studied and compared with those of their chlorinated analogues. Introduction In the last decades, extensive research has been per- formed on the microbial dehalogenation of chlorinated ethenes, especially of tetrachloroethene (PCE) and trichloroethene (TCE). Different anaerobes such as Sul- furospirillum multivorans or Desulfitobacterium hafniense PCE-S are able to grow with PCE or TCE as electron acceptor for catabolic oxidation reactions with cis-1,2- dichloroethene as the final product (Scholz-Muramatsu et al., 1995; Miller et al., 1998). The dehalogenation of chlorinated ethenes, which is coupled to energy conser- vation in a respiratory process (organohalide respiration), is catalysed by the tetrachloroethene reductive dehaloge- nase (PCE dehalogenase). Besides chlorinated ethenes, only chlorinated propenes were found to be dechlorinated by the native enzyme; however, the latter compounds did not support growth (Neumann et al., 2002; Schmitz et al., 2007). Evidence was presented that the chlorinated ethenes are dechlorinated via an external electron trans- fer reaction involving radical intermediates (Schmitz et al., 2007). Whereas several studies on the dechlorination of chlo- rinated alkenes exist, nothing is known so far on the microbial debromination of brominated ethenes, which have been reported to be contaminants of soil and groundwater (Patterson et al., 2007; Grigoriadou et al., 2008) as well as natural products of marine algae (Mar- shall et al., 1999). Brominated ethenes were shown to be toxic, potential carcinogens, mutagens and central nervous system depressants (Benya et al., 1982; Canton and Wegman, 1983; Cohen et al., 2009). The slow deha- logenation of brominated ethenes reported so far (Blay and Daniels, 1987; Patterson et al., 2007; Cohen et al., 2009) is presumably due to abiotic conversion mediated by metals or metal-containing cofactors as reported also, for example, for the conversion of halogenated methanes (see, for example, Krone et al., 1989a,b). Little is known about the biological reductive debromination. Here we report on the dehalogenation of brominated ethenes and propenes mediated by the PCE dehaloge- nases of S. multivorans and D. hafniense PCE-S. To our knowledge, the study presented here is the first to describe enzymatic rather than abiotic debromination with Received 21 July, 2009; accepted 10 September, 2009. *For correspondence. E-mail gabriele.diekert@uni-jena.de; Tel. (+49) 3641 949300; Fax (+49) 3641 949302. † Present address: Institute for General Microbiology, Christian Albrechts University, Am Botanischen Garten 1-9, 24118 Kiel, Germany. This work is dedicated to Professor Dr R.K. Thauer on the occasion of his 70th birthday. Environmental Microbiology (2010) 12(2), 501–509 doi:10.1111/j.1462-2920.2009.02093.x © 2009 Society for Applied Microbiology and Blackwell Publishing Ltd