Long-Term Field Study of Microbial Community and Dechlorinating Activity Following Carboxymethyl Cellulose-Stabilized Nanoscale Zero-Valent Iron Injection

Abstract

Nanoscale zerovalent iron (nZVI) is an emerging technology for the remediation of contaminated sites. However, there are concerns related to the impact of nZVI on in situ microbial communities. In this study, the microbial community composition at a contaminated site was monitored over two years following the injection of nZVI stabilized with carboxymethyl cellulose (nZVI-CMC). Enhanced dechlorination of chlorinated ethenes to nontoxic ethene was observed long after the expected nZVI oxidation. The abundance of Dehalococcoides (Dhc) and vinyl chloride reductase (vcrA) genes, monitored using qPCR, increased by over an order of magnitude in nZVI-CMC-impacted wells. The entire microbial community was tracked using 16S rRNA gene amplicon pyrosequencing. Following nZVI-CMC injection, a clear shift in microbial community was observed, with most notable increases in the dechlorinating genera Dehalococcoides and Dehalogenimonas. This study suggests that coupled abiotic degradation (i.e., from reaction with nZVI) and biotic degradation fueled by CMC led to the long-term degradation of chlorinated ethenes at this field site. Furthermore, nZVI-CMC addition stimulated dehalogenator growth (e.g., Dehalococcoides) and biotic degradation of chlorinated ethenes.

Geochemical and microbial community determinants of reductive dechlorination at a site biostimulated with glycerol

“…Interestingly, the study of Kocur et al . () showed dominance of OD1 where the environment was not strongly reduced (−80 to −140 mV). This may explain their increased relative abundance at a later aquifer biostimulation stage when the redox potential increased and organic‐rich condition faded.…”

“…Members of the candidate phylum OD1 (also known as Parcubacteria) (Brown et al ., ) have mostly been connected with suboxic and anoxic pristine sulfur‐rich environments (Elshahed et al ., ; Briée et al ., ; Peura et al ., ). However, OD1 (Gihring et al ., ; Kocur et al ., ) and another candidate division, OP11 (Microgenomates), (Lee et al ., ) also appeared at a later stage during aquifer biostimulation for uranium and CE bioremediation (Elshahed et al ., ; Wrighton et al ., ). Interestingly, the study of Kocur et al .…”

Extrachromosomal circular elements targeted by CRISPR-Cas in Dehalococcoides mccartyi are linked to mobilization of reductive dehalogenase genes

“…Active circularization of extrachromosomal elements, particularly the island containing the vcrABC operon, was inferred from sequence data and confirmed by polymerase chain reaction (PCR), providing the first clues to a mechanism for lateral transfer of DNA in D. mccartyi. The existence of a circular form of the genomic island (GI) containing the vcrABC operon also explains the periodic observation of higher vcrA to 16S rRNA gene copies in DNA samples from field sites [22,23]. We have gained new insights to lateral transfer of dehalogenase genes, discovered new mobile elements and their connection with CRISPR-Cas systems in D. mccartyi.…”

Microbial Communities Associated with Sustained Anaerobic Reductive Dechlorination of α-, β-, γ-, and δ-Hexachlorocyclohexane Isomers to Monochlorobenzene and Benzene

“…Amplicon Sequencing For pyrotag sequencing, the hypervariable V6 to V8 region of the 16S rRNA gene of bacteria, archaea and the 18S rRNA gene in eukaryote was amplified using PCR reactions with the primer set 926f (5'-AAA CTY AAA KGA ATT GAC GG-3') and S9 1392r (5'-ACG GGC GGT GTG TRC-3') (Engelbrektson et al 2010;Hanshew et al 2013) on a MJ Research PTC-200 Peltier Thermal Cycler (Bio-Rad Laboratories, Hercules, CA). The thermocycling program is as follows: 95 ℃, 3min; 25 cycles of 90 ℃ 30s, 54℃ 45s, 72℃ 10min; final hold at 4℃ (Kocur et al 2016). The forward and reverse primers also included 30 bp adaptors sequences (CCA TCT CAT CCC TGC GTG TCT CCG ACT CAG; CCT ATC CCC TGT GTG CCT TGG CAG TCT CAG, respectively).…”