Abstract
Dehalococcoides mccartyi strain BTF08 has the unique property to couple complete dechlorination of tetrachloroethene and 1,2-dichloroethane to ethene with growth by using the halogenated compounds as terminal electron acceptor. The genome of strain BTF08 encodes 20 genes for reductive dehalogenase homologous proteins (RdhA) including those described for dehalogenation of tetrachloroethene (PceA, PteA), trichloroethene (TceA) and vinyl chloride (VcrA). Thus far it is unknown under which conditions the different RdhAs are expressed, what their substrate specificity is and if different reaction mechanisms are employed. Here we found by proteomic analysis from differentially activated batches that PteA and VcrA were expressed during dechlorination of tetrachloroethene to ethene, while TceA was expressed during 1,2-dichloroethane dehalogenation. Carbon and chlorine compound-specific stable isotope analysis suggested distinct reaction mechanisms for the dechlorination of (i) cis-dichloroethene and vinyl chloride versus (ii) tetrachloroethene. This differentiation was observed independent of the expressed RdhA proteins. Differently, two stable isotope fractionation patterns were observed for 1,2-dichloroethane transformation, for cells with distinct RdhA inventories. Conclusively, we could link specific RdhA expression with functions and provide an insight into the apparently substrate-specific reaction mechanisms in the pathway of reductive dehalogenation in D. mccartyi strain BTF08. Data are available via ProteomeXchange with identifiers PXD018558 and PXD018595.
Highlights
Chlorinated organic contaminants, such as tetrachloroethene (PCE), belong to the most frequent groundwater contaminants entering the environment through accidents, improper handling and waste disposal (Carter et al, 2008)
Dehalococcoides mccartyi strain BTF08 was cultivated on PCE, cDCE, vinyl chloride (VC) or 1,2-DCA as electron acceptor after growth for at least four transfers with one constant electron acceptor, either PCE, cDCE, VC or 1,2-DCA (Supplementary Figures S1A–C)
D. mccartyi strain BTF08 adapted fast, with no obvious delay in dehalogenation compared to controls maintained on the same substrate, when the electron acceptor was switched in most cases (Table 1)
Summary
Chlorinated organic contaminants, such as tetrachloroethene (PCE), belong to the most frequent groundwater contaminants entering the environment through accidents, improper handling and waste disposal (Carter et al, 2008). Dehalococcoides mccartyi strain BTF08 harbors the unique property to couple all reductive dehalogenation steps starting from PCE down to ethene to growth referred to as organohalide respiration (Cichocka et al, 2010; Kaufhold et al, 2013). Its genome contains 20 reductive dehalogenase homologous gene clusters (rdhAB) wherefrom 16 rdhAB genes belong to classified orthologue groups being conserved throughout cultivated D. mccartyi strains (Hug et al, 2013). The rdhAB genes in strain BTF08 include orthologues of pceA, tceA, and vcrA, proposed to be involved in PCE, TCE, and vinyl chloride (VC) dehalogenation, respectively, while the other rdhA genes can currently not be functionally assigned. D. mccartyi strain BTF08 possesses all RdhA encoding genes required for complete reductive dehalogenation of PCE to ethene (Pöritz et al, 2013). Functional annotation of the rdhA genes in strain BTF08 has been done on the basis of their affiliation to orthologue groups containing biochemically characterized orthologues in other D. mccartyi strains (Hug et al, 2013), but the biochemical activity has not been confirmed experimentally in D. mccartyi strain BTF08
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