Bioaugmentation with DistinctDehalobacterStrains Achieves Chloroform Detoxification in Microcosms

Abstract

Chloroform (CF) is a widespread groundwater contaminant not susceptible to aerobic degradation. Under anoxic conditions, CF can undergo abiotic and cometabolic transformation but detoxification is generally not achieved. The recent discovery of distinct Dehalobacter strains that respire CF to dichloromethane (DCM) and ferment DCM to nonchlorinated products promises that bioremediation of CF plumes is feasible. To track both strains, 16S rRNA gene-based qPCR assays specific for either Dehalobacter strain were designed and validated. A laboratory treatability study explored the value of bioaugmentation and biostimulation to achieve CF detoxification using anoxic microcosms established with aquifer material from a CF-contaminated site. Microcosms that received 6% (v/v) of the CF-to-DCM-dechlorinating culture Dhb-CF to achieve an initial Dehalobacter cell titer of 1.6 ± 0.9 × 10(4) mL(-1) dechlorinated CF to stoichiometric amounts of DCM. Subsequent augmentation with 3% (v/v) of the DCM-degrading consortium RM to an initial Dehalobacter cell abundance of 1.2 ± 0.2 × 10(2) mL(-1) achieved complete DCM degradation in microcosms amended with 10 mM bicarbonate. Growth of the CF-respiring and the DCM-degrading Dehalobacter populations and detoxification were also observed in microcosms that received both inocula simultaneously. These findings suggest that anaerobic bioremediation (e.g., bioaugmentation) is a possible remedy at CF- and DCM-contaminated sites without CT, which strongly inhibited CF organohalide respiration and DCM organohalide fermentation.

Mutualistic interaction between dichloromethane‐ and chloromethane‐degrading bacteria in an anaerobic mixed culture

“…The feasibility of bioaugmentation for chloroform and DCM detoxification has been demonstrated (Justicia‐Leon et al ., ), and the findings reported here highlight that chloroform remediation can be sustained without biostimulation (i.e., electron donor addition) because the degradation of the daughter product DCM generates the H 2 required for chloroform reductive dechlorination. A logical extension of this concept is that DCM serves as an indirect electron donor (i.e., a source of H 2 and acetate) to support other reductive processes such as nitrate reduction, organohalide respiration, iron reduction, sulfate reduction, methanogenesis and reductive acetogenesis (Fig.…”

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

“…Dehalobacter species are regarded as specialist dehalogenating bacteria able to use a wide variety of aliphatic and aromatic organochlorines as terminal electron acceptors (Nelson et al, 2014), the exceptions being Dehalobacter lineages shown to ferment DCM to acetate and hydrogen (Lee et al, 2012;Justicia-Leon et al, 2014). Strain UNSWDHB could not ferment DCM (0.2 mM) when supplied as the sole source of organic carbon and electrons after 4 weeks of observation.…”

“…Moreover, microbial communities comprising both TCM respiring and dichloromethane (DCM) fermenting bacteria have shown that complete TCM dechlorination is a feasible bioaugmentation strategy. (Lee et al ., ; Justicia‐Leon et al ., )…”

“…Moreover, microbial communities comprising both TCM respiring and dichloromethane (DCM) fermenting bacteria have shown that complete TCM dechlorination is a feasible bioaugmentation strategy. (Lee et al, 2012;Justicia-Leon et al, 2014) Dehalobacter strain CF (yet to be isolated) and Desulfitobacterium strain PR originate from chlorinated ethane contaminated environments and have been shown to also use 1,1,1-trichloroethane (1,1,1-TCA) in addition to TCM. Both organisms express a reductive dehalogenase (RDase) with a 95% amino acid identity, shown to be responsible for dechlorination of both compounds [i.e.…”

Unravelling long-term source removal effects and chlorinated methanes natural attenuation processes by C and Cl stable isotopic patterns at a complex field site

“…CT and CF inhibit mutual biodegradation (Grostern et al, 2010;Lima and Sleep, 2010;Justicia-Leon et al, 2014) and also microbial respiration of chlorinated ethanes and ethenes by Dehalococcoides and Desulfitobacterium species (Bagley et al, 2000;Weathers and Parkin, 2000;Maymó-Gatell et al, 2001;Duhamel et al, 2002;Futagami et al, 2006Futagami et al, , 2013, and this hinders natural attenuation and bioremediation strategies in complex sites impacted by mixtures of chlorinated compounds.…”