Reductive dechlorination of trichloroethene at concentrations approaching saturation by a Desulfitobacterium-containing community

Abstract

In dense nonaqueous phase liquid (DNAPL) contaminant source zones, aqueous concentrations of trichloroethene (TCE) in groundwater may approach saturation levels (8.4 mM). It is generally believed that such saturation concentrations are toxic to organohalide-respiring bacteria (OHRB), thus limiting the effectiveness of bioremediation. Here, we describe a Desulfitobacterium-containing culture capable of dechlorinating TCE to cis-dichloroethene (cis-DCE) at aqueous concentrations as high as 8.0 mM. A novel Desulfitobacterium population, designated as strain THU1, was identified by the 16S rRNA gene-targeted polymerase chain reaction and Illumina MiSeq sequencing. Microbial community analysis revealed that TCE concentrations above 4.6 mM significantly affected the composition of the microbial community but had little effect on the Shannon index. The genome of strain THU1 revealed two reductive dehalogenases (RdhA), and the RdhA2 is a putative pceA. Additionally, its genome encodes proteins involved in stress response and regulatory pathways, enabling tolerance to near-saturation TCE concentrations. Our findings provide insights into the metabolic flexibility of Desulfitobacterium, suggesting its potential use as a candidate for source zone bioremediation to enhance the dissolution of TCE DNAPL by increasing the concentration gradient at the DNAPL-water interface.

Keywords: DNAPL; Desulfitobacterium; Reductive dechlorination; Saturation concentration; TCE.