A Desulfitobacterium sp. strain PR reductively dechlorinates both 1,1,1‐trichloroethane and chloroform

Abstract

1,1,1-Trichloroethane (TCA) and chloroform are two notorious groundwater pollutants. Here we report the isolation and characterization of Desulfitobacterium sp. strain PR that rapidly dechlorinates both compounds. In pyruvate-amended medium, strain PR reductively dechlorinates ∼ 1.0 mM TCA completely to monochloroethane within 15 days. Under the same conditions, strain PR dechlorinates ∼ 1.2 mM chloroform to predominantly dichloromethane (∼ 1.14 mM) and trace amount of monochloromethane (∼ 0.06 mM) within 10 days. Strain PR shares 96.7% 16S rRNA gene sequence similarity with its closest relative - Desulfitobacterium metallireducens strain 853-15; however, it distinguishes itself from known Desulfitobacterium strains by its inability of utilizing several of their commonly shared substrates such as lactate, thiosulfate and sulfite. A reductive dehalogenase gene (ctrA) in strain PR was identified to be responsible for dechlorination of both TCA and chloroform, showing a maximum expression level of 5.95 ∼ 6.25 copies of transcripts cell(-1) . CtrA shares 94% amino acid sequence identity with CfrA in Dehalobacter sp. strain CF50 and DcrA in Dehalobacter sp. strain DCA. Interestingly, strain PR could tolerate high aqueous concentrations (up to 0.45 mM) of trichloroethene, another groundwater pollutant that often coexists with TCA/chloroform. As the first chloroform-respiring and the second TCA-respiring isolate that has been identified, Desulfitobacterium sp. strain PR may prove useful in remediation of halogenated alkanes with trihalomethyl (-CX₃) groups.

Subtle changes in the active site architecture untangled overlapping substrate ranges and mechanistic differences of two reductive dehalogenases

“…This observation is consistent with the inability of DcaA to convert VC or MCA as substrate and is also in line with earlier studies on growing cultures of D. dichloroeliminans DCA1 [26]. So far, an RDase-mediated conversion of 1,1,1-TCA was only reported for chloroform RDases, which are distantly related to DcaA and PceA [14,33,34]. 1).…”

“…The exchange of Arg357 to Gln displayed a rather negligible effect on both mechanisms (Fig. However, comparison of protein sequences revealed the replacement of the tyrosine by a cysteine or phenylalanine in RDases specialized on the halogen substitution at chloromethanes [14,33,34] (Fig. In addition, the positive effect on TBE conversion, as it was shown for the respective PceA mutant, was not observed in this case, indicating structural differences at the active sites of both enzymes leading to a different substrate positioning.…”

Purinyl-cobamide is a native prosthetic group of reductive dehalogenases

“…Members of the genus Desulfitobacterium ( Dsf ) are strictly anaerobic, metabolically versatile, Gram-positive bacteria common in subsurface environments, where they contribute to the reductive dehalogenation of organohalogens, including groundwater contaminants such as chlorinated solvents 14,15 . The tetrachloroethene (PCE) RDases have a strict requirement for cobamide as a prosthetic group and generate predominantly cis -1,2-dichloroethene ( c DCE) and inorganic chloride as products 16 .…”

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

“…Both organisms express a reductive dehalogenase (RDase) with a 95% amino acid identity, shown to be responsible for dechlorination of both compounds [i.e. CfrA (strain CF), CtrA strain PR) (Tang et al ., ; Ding et al ., )]. It should also be noted that these TCM and 1,1,1‐TCA RDases have low amino acid identity with other RDases (<60%) (Tang and Edwards, ).…”