Impact of Fixed Nitrogen Availability on Dehalococcoides mccartyi Reductive Dechlorination Activity

• Published in: Environmental science & technology Vol. 53; no. 24; pp. 14548 - 14558
• Main Authors: Kaya, Devrim, Kjellerup, Birthe V, Chourey, Karuna, Hettich, Robert L, Taggart, Dora M, Löffler, Frank E
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 17.12.2019; American Chemical Society (ACS)
• Subjects: BASIC BIOLOGICAL SCIENCES; Biodegradation, Environmental; Chloroflexi; Dechlorination; Ethene; Ethylene; Ethylenes; Fixation; Fluvial sediments; Gene expression; genetics; Groundwater; groundwaters; monomers; Nitrogen; Nitrogenase; Nitrogenation; Nitrous oxide; peptides and proteins; Polymerase chain reaction; Proteomics; reductive dechlorination; Relative abundance; Rivers; RNA, Ribosomal, 16S; rRNA 16S; Vinyl Chloride
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/acs.est.9b04463

Biostimulation to promote reductive dechlorination is widely practiced, but the value of adding an exogenous nitrogen (N) source (e.g., NH4 +) during treatment is unclear. This study investigates the effect of NH4 + availability on organohalide-respiring Dehalococcoides mccartyi (Dhc) growth and reductive dechlorination in enrichment cultures derived from groundwater (PW4) and river sediment (TC) impacted with chlorinated ethenes. In PW4 cultures, the addition of NH4 + increased cis-1,2-dichloroethene (cDCE)-to-ethene dechlorination rates about 5-fold (20.6 ± 1.6 versus 3.8 ± 0.5 μM Cl– d‑1), and the total number of Dhc 16S rRNA gene copies were about 43-fold higher in incubations with NH4 + ((1.8 ± 0.9) × 108 mL–1) compared to incubations without NH4 + ((4.1 ± 0.8) × 107 mL–1). In TC cultures, NH4 + also stimulated cDCE-to-ethene dechlorination and Dhc growth. Quantitative polymerase chain reaction (qPCR) revealed that Cornell-type Dhc capable of N2 fixation dominated PW4 cultures without NH4 +, but their relative abundance decreased in cultures with NH4 + amendment (i.e., 99 versus 54% of total Dhc). Pinellas-type Dhc incapable of N2 fixation were responsible for cDCE dechlorination in TC cultures, and diazotrophic community members met their fixed N requirement in the medium without NH4 +. Responses to NH4 + were apparent at the community level, and N2-fixing bacterial populations increased in incubations without NH4 +. Quantitative assessment of Dhc nitrogenase genes, transcripts, and proteomics data linked Cornell-type Dhc nifD and nifK expression with fixed N limitation. NH4 + additions also demonstrated positive effects on Dhc in situ dechlorination activity in the vicinity of well PW4. These findings demonstrate that biostimulation with NH4 + can enhance Dhc reductive dechlorination rates; however, a “do nothing” approach that relies on indigenous diazotrophs can achieve similar dechlorination end points and avoids the potential for stalled dechlorination due to inhibitory levels of NH4 + or transformation products (i.e., nitrous oxide).