Reductive Dechlorination of Tetrachloroethene to Ethene by a Two-Component Enzyme Pathway

Abstract

Two membrane-bound, reductive dehalogenases that constitute a novel pathway for complete dechlorination of tetrachloroethene (perchloroethylene [PCE]) to ethene were partially purified from an anaerobic microbial enrichment culture containing Dehalococcoides ethenogenes 195. When titanium(III) citrate and methyl viologen were used as reductants, PCE-reductive dehalogenase (PCE-RDase) (51 kDa) dechlorinated PCE to trichloroethene (TCE) at a rate of 20 μmol/min/mg of protein. TCE-reductive dehalogenase (TCE-RDase) (61 kDa) dechlorinated TCE to ethene. TCE,cis-1,2-dichloroethene, and 1,1-dichloroethene were dechlorinated at similar rates, 8 to 12 μmol/min/mg of protein. Vinyl chloride and trans-1,2-dichloroethene were degraded at rates which were approximately 2 orders of magnitude lower. The light-reversible inhibition of TCE-RDase by iodopropane and the light-reversible inhibition of PCE-RDase by iodoethane suggest that both of these dehalogenases contain Co(I) corrinoid cofactors. Isolation and characterization of these novel bacterial enzymes provided further insight into the catalytic mechanisms of biological reductive dehalogenation.

TheDesulfitobacteriumgenus

“…It was also shown with other chloridogenesis bacteria, such as Desulfomonile tiedjei DCB-1, Dehalococcoides ethenogenes, Desulfitobacterium sp. strain PCE-S, Dehalobacter restrictus and Sulfurospirullum multivorans, that hydrogenases or formate dehydrogenases, facing the outside of the cytoplasmic membrane, were associated as components of an electron-donating enzymatic system (Schumacher & Holliger, 1996;Miller et al, 1997aMiller et al, , 1998Magnuson et al, 1998;Louie & Mohn, 1999). Furthermore, cytochromes and quinones have been pro-posed to be involved in the electron transfer from the hydrogenases to Rdhases and in the generation of the proton gradient (Fig.…”

Reductive dechlorination in the energy metabolism of anaerobic bacteria

“…Two membrane-bound reductive dehalogenases have been puri¢ed via gel electrophoresis from a mixed enrichment culture containing Dehalococcoides ethenogenes [61]. The PCE reductive dehalogenase (51 kDa) mediates PCE reduction to TCE, and the TCE reductive dehalogenase (61 kDa) TCE reduction to ethene.…”

Isolation of two new Dehalococcoides mccartyi strains with dissimilar dechlorination functions and their characterization by comparative genomics via microarray analysis

“…Central metabolic functions for Dhc growth in anaerobic environments are mostly encoded by genes within the core genome, while genes encoding the reductive dehalogenases (RDases) for chlorinated ethene reduction are located within the HPRs or GEIs (Kube et al, 2005;Seshadri et al, 2005;McMurdie et al, 2009). A combined total of 121 putative RDase-encoding genes (including truncated ones) have been identified in the five sequenced genomes of strains 195, CBDB1, BAV1, VS and GT and to date, only four of them (pceA, tceA, vcrA, bvcA) have been demonstrated to code for proteins with chlorinated ethene functions (Magnuson et al, 1998;Krajmalnik-Brown et al, 2004;Müller et al, 2004). However, the large pool of putative Dhc RDases remains a significant reservoir of biochemical potential for transforming a wide variety of anthropogenic and natural organohalides (Fennell et al, 2004;Adrian et al, 2007b).…”