Metagenomic Analysis Reveals Microbial Interactions at the Biocathode of a Bioelectrochemical System Capable of Simultaneous Trichloroethylene and Cr(VI) Reduction

Abstract

Bioelectrochemical systems (BES) are attractive and versatile options for the bioremediation of organic or inorganic pollutants, including trichloroethylene (TCE) and Cr(VI), often found as co-contaminants in the environment. The elucidation of the microbial players’ role in the bioelectroremediation processes for treating multicontaminated groundwater is still a research need that attracts scientific interest. In this study, 16S rRNA gene amplicon sequencing and whole shotgun metagenomics revealed the leading microbial players and the primary metabolic interactions occurring in the biofilm growing at the biocathode where TCE reductive dechlorination (RD), hydrogenotrophic methanogenesis, and Cr(VI) reduction occurred. The presence of Cr(VI) did not negatively affect the TCE degradation, as evidenced by the RD rates estimated during the reactor operation with TCE (111±2 μeq/Ld) and TCE/Cr(VI) (146±2 μeq/Ld). Accordingly, Dehalococcoides mccartyi, the primary biomarker of the RD process, was found on the biocathode treating both TCE (7.82E+04±2.9E+04 16S rRNA gene copies g−1 graphite) and TCE/Cr(VI) (3.2E+07±2.37E+0716S rRNA gene copies g−1 graphite) contamination. The metagenomic analysis revealed a selected microbial consortium on the TCE/Cr(VI) biocathode. D. mccartyi was the sole dechlorinating microbe with H2 uptake as the only electron supply mechanism, suggesting that electroactivity is not a property of this microorganism. Methanobrevibacter arboriphilus and Methanobacterium formicicum also colonized the biocathode as H2 consumers for the CH4 production and cofactor suppliers for D. mccartyi cobalamin biosynthesis. Interestingly, M. formicicum also harbors gene complexes involved in the Cr(VI) reduction through extracellular and intracellular mechanisms.

Microbiome Composition and Dynamics of a Reductive/Oxidative Bioelectrochemical System for Perchloroethylene Removal: Effect of the Feeding Composition

“…In line with kinetic performances, in the reductive compartment of the BES fed with MM or SG, D. mccartyi was abundant (2.5E + 07 and 1.8E + 07 16S rRNA gene copies/L respectively under MM and SG feeding) and was mainly represented by tceA -carrying strains. D. mccartyi was responsible for the biological RD occurring in the reductive compartment, likely via an indirect electron transfer mechanism, but this microorganism has not been considered an electroactive bacterium until now ( Matturro et al, 2021 ). Regarding microbiome composition, Epsilonbacteraeota members were dominant (50.8 and 89.5% under MM and SG, respectively) and mostly affiliated to one ASV that showed 99.5% of identity to Sulfuricurvum kujiensestrain YK-3 (GenBank: AB080644) ( Kodama and Watanabe, 2003 ).…”

Coupled Adsorption and Biodegradation of Trichloroethylene on Biochar from Pine Wood Wastes: A Combined Approach for a Sustainable Bioremediation Strategy

“…A total of 4 ng of DNA extracted from each sample was used for 16S rRNA gene amplicon sequencing. The amplicon library was prepared to target the V1-V3 variable regions, as previously described [53]. PCR reactions were performed in 25 µL total volume containing Phusion High Fidelity Master Mix (Thermo Fisher Scientific, Rodano, Italy) and 0.5 µM final concentration of the library adaptors with V1-V3 primers (bacteria 27F: 5 -AGAGTTTGATCCTGGCTCAG-3 and 534R: 5 -ATTACCGCGGCTGCTGG-3 ).…”

Marine Dehalogenator and Its Chaperones: Microbial Duties and Responses in 2,4,6-Trichlorophenol Dechlorination

“…In vitro and pure culture experiments have suggested that several HOCs are directly dehalogenated via coenzyme F430, − a nickel­(II) porphyrinoid involved in the final step of methanogenesis as a cofactor of methyl-CoM reductase. A recent metagenomic study also assumed that methanogens may provide the upstream precursor for cobalamin biosynthesis in OHRB . In contrast, methanogens consume a large amount of H 2 (an electron donor for both methanogenesis and dehalogenation) , and may compete with OHRB for corrinoids in mixed dehalogenating cultures .…”