Relative Contributions of Dehalobacter and Zerovalent Iron in the Degradation of Chlorinated Methanes

Abstract

The role of bacteria and zerovalent iron (Fe(0)) in the degradation of chlorinated solvents in subsurface environments is of interest to researchers and remediation practitioners alike. Fe(0) used in reactive iron barriers for groundwater remediation positively interacted with enrichment cultures containing Dehalobacter strains in the transformation of halogenated methanes. Chloroform transformation and dichloromethane formation was up to 8-fold faster and 14 times higher, respectively, when a Dehalobacter-containing enrichment culture was combined with Fe(0) compared with Fe(0) alone. The dichloromethane-fermenting culture transformed dichloromethane up to three times faster with Fe(0) compared to without. Compound-specific isotope analysis was employed to compare abiotic and biotic chloroform and dichloromethane degradation. The isotope enrichment factor for the abiotic chloroform/Fe(0) reaction was large at -29.4 ± 2.1‰, while that for chloroform respiration by Dehalobacter was minimal at -4.3 ± 0.45‰. The combined abiotic/biotic dechlorination was -8.3 ± 0.7‰, confirming the predominance of biotic dechlorination. The enrichment factor for dichloromethane fermentation was -15.5 ± 1.5‰; however, in the presence of Fe(0) the factor increased to -23.5 ± 2.1‰, suggesting multiple mechanisms were contributing to dichloromethane degradation. Together the results show that chlorinated methane-metabolizing organisms introduced into reactive iron barriers can have a significant impact on trichloromethane and dichloromethane degradation and that compound-specific isotope analysis can be employed to distinguish between the biotic and abiotic reactions involved.

Isolation and characterization of Dehalobacter sp. strain UNSWDHB capable of chloroform and chlorinated ethane respiration

“…This hypothesis is supported by carbon stable isotope ratio data. Recently we found that 12 C/ 13 C fractionation was minimal during TCM respiration by strain UNSWDHB ( ε = −4.3‰) compared CfrA in strain CF ( ε = −28‰) (Chan et al ., ; Lee et al ., ). Masking of the kinetic isotope effect has been show for highly efficient enzymes (Lollar et al ., ), the low enrichment factor indicates a that TmrA is highly efficient at TCM dechlorination compared to CfrA.…”

“…Although this comparison is error prone without standardising the concentration of RDases, the data may explain the difference in 13 C/ 12 C fractionation observed during TCM dechlorination by these two strains (i.e. 24.3& 6 0.45& and 227& 6 0.9& for strains UNSWDHB and CF respectively (Chan et al, 2012;Lee et al, 2015). The increased RDase efficiency observed in strain UNSWDHB could lead to masking of the kinetic isotope effect (KIE).…”

Vitamin B12 effects on chlorinated methanes-degrading microcosms: Dual isotope and metabolically active microbial populations assessment

“…CT and CF reduction involves one or two C-Cl bond cleavages in the first rate-limiting step 450 (Elsner et al, 2004;Chan et al, 2012;Lee et al, 2015). For AKIE calculations one C-Cl bond 451 cleavage was assumed and the determined Ɛ values (R 2 ≥0.9) were used (Table 3, Fig.…”

Carbon and Chlorine Isotope Fractionation Patterns Associated with Different Engineered Chloroform Transformation Reactions

“…In the case of PS, the anaerobic environment that is created following the consumption of the oxidant is ideal for CF microbial dehalogenation under sulfate reduction conditions to be enhanced. Enhanced CF bioremediation has also been observed when combining Fe(0) and methanogens that use the cathodic hydrogen generated by iron corrosion for cometabolic degradation of CF [83][84][85] or even better by dehalorespiring bacteria which are not inhibited at certain concentrations of CF 29 . Therefore, there would be an increasing number of case studies, where CF degradation due to PS application or Although CF anaerobic biodegradation has been reported to occur mainly via cometabolic dechlorination or by dehalorespiration 8 , an alternative pathway was suggested in the presence of cobalamins and involving CF hydrolysis 87,88 .…”