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Characterisation of microbial dehalogenation using compound specific stable isotope analysis

Subject Area Metabolism, Biochemistry and Genetics of Microorganisms
Term from 2011 to 2018
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 171475307
 
Final Report Year 2020

Final Report Abstract

Wichtigste Ergebnisse: The effect of intracellular microscale mass transfer on microbial carbon isotope fractionation of tetrachloroethene (PCE) and trichloroethene (TCE) was investigated. Conclusively, ratelimiting mass transfer barriers were (a) the outer membrane or cell wall and (b) the cytoplasmic membrane in case of a cytoplasmic location of the RDase enzyme. Overall, our results indicate that masking of isotope fractionation is determined by (1) hydrophobicity of the degraded compound, (2) properties of the cell envelope, and (3) the localization of the reacting enzyme. - The role of the corrinoid cofactor in reductive dehalogenation catalysis by tetrachloroethene reductive dehalogenase (PceA) of Sulfurospirillum multivorans was investigated using isotope analysis of carbon and chlorine. Our results suggest mechanistic and/or kinetic differences in catalytic PCE dehalogenation by enzymes and different corrinoids, whereas such differences were not observed for TCE. - The anaerobic transformation of 1,2-DCA by Dehalococcoides mccartyi strain 195 and strain BTF08 was analysed using triple-element compound-specific stable isotope analysis (CSIA) of carbon, chlorine and hydrogen for the first time. Isotope fractionation patterns for carbon and chlorine within both investigated D. mccartyi strains, as well as the dual-element analysis, supported identical reaction mechanisms for dehalogenation of 1,2-DCA. Hydrogen isotope fractionation analysis revealed dihaloelimination as prevalent reaction mechanism. - Proteomic analysis indicates that only PteA and VcrA are needed for the complete dehalogenation of PCE to ethene. TceA was induced in presence of 1,2-DCA, however not in presence of chlorinated ethenes. - A mechanistic dichotomy was detected for bacterial TCE dechlorination using dual-element carbon and chlorine analysis. Depending on cultivation conditions and microbial community present, the dechlorination reaction was proposed to run either via an initial Cl elimination with subsequent protonation or via an initial protonation with subsequent dechlorination. - For Dehalococcoides mccartyi strain BTF08, the reductive dechlorination of PCE was proposed to run via an initial Cl elimination while the initial step for VC and cis-DCE dechlorination was proposed to be a protonation step. The observation was independent of the reductive dehalogenases present. - Based on dual-element C/Cl stable isotope analysis, different patterns and presumably different reactions were concluded for dechlorination of 1,2-DCA in presence of VcrA or TceA, respectively. - A new LC/IRMS method for the quantitative determination of halogenated benzoates was developed. Characterisation of growth and carbon stable isotope analysis, suggested that dehalogenation of para-halobenzoic acids by Thauera chlorobenzoica strain 3CB-1T follows a different mechanism from that of meta-halobenzoic acids.

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