Microbial reductive dehalogenation of trihalomethanes by a Dehalobacter-containing co-culture

Abstract

Trihalomethanes such as chloroform and bromoform, although well-known as a prominent class of disinfection by-products, are ubiquitously distributed in the environment due to widespread industrial usage in the past decades. Chloroform and bromoform are particularly concerning, of high concentrations detected and with long half-lives up to several hundred days in soils and groundwater. In this study, we report a Dehalobacter- and Desulfovibrio-containing co-culture that exhibits dehalogenation of chloroform (~0.61 mM) to dichloromethane and bromoform (~0.67 mM) to dibromomethane within 10-15 days. This co-culture was further found to dechlorinate 1,1,1-trichloroethane (1,1,1-TCA) (~0.65 mM) to 1,1-dichloroethane within 12 days. The Dehalobacter species present in this co-culture, designated Dehalobacter sp. THM1, was found to couple growth with dehalogenation of chloroform, bromoform, and 1,1,1-TCA. Strain THM1 harbors a newly identified reductive dehalogenase (RDase), ThmA, which catalyzes chloroform, bromoform, and 1,1,1-TCA dehalogenation. Additionally, based on the sequences of thmA and other identified chloroform RDase genes, ctrA, cfrA, and tmrA, a pair of chloroform RDase gene-specific primers were designed and successfully applied to investigate the chloroform dechlorinating potential of microbial communities. The comparative analysis of chloroform RDases with tetrachloroethene RDases suggests a possible approach in predicting the substrate specificity of uncharacterized RDases in the future.

Proteogenomics Reveals Novel Reductive Dehalogenases and Methyltransferases Expressed during Anaerobic Dichloromethane Metabolism

“…RDases that only share a maximum of 29.8% pairwise identity (range, 20.9 to 29.8%) can dechlorinate the same substrate, i.e., tetrachloroethene (41). On the other hand, even minor sequence variations can result in distinct RDase substrate specificity (39,42), thus making substrate range prediction based on sequence similarity a daunting task.…”

Using cell yields and qPCR to estimate biotic contribution to 1,1,1-trichloroethane dechlorination at a field site treated with granular zero valent iron and guar gum

“…to CfrA (i.e., able to target 1,1,1-TCA but not 1,1-DCA) (Tang and Edwards, 2013B; Zhao et al, 2017). 251…”

“…Dehalobacter sp. strain THM1 (Zhao et al, 2017), and Desulfitobacterium strain PR (Ding et al, 2014), 61 have since been described or isolated with the ability to partially or completely dechlorinate 1,1,1-TCA 62 and/or 1,1-DCA. All of these strains use either hydrogen or formate as electron donor.…”

Treatments for color removal from wastewater: State of the art

“…Trihalomethanes (THMs) such as chloroform and bromoform (Droste and Gehr, 2018;Zhao et al, 2017). Some of these show mutagenic properties and are known to be carcinogenic to humans (Sakarinen, 2016).…”