Impact of Fixed Nitrogen Availability on Dehalococcoides mccartyi Reductive Dechlorination Activity
[1];
[3];
[5]
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States); Univ. of Maryland, College Park, MD (United States)
- Univ. of Maryland, College Park, MD (United States)
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Microbial Insights, Inc., Knoxville, TN (United States)
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States)
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. Finally, 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).
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE
- Grant/Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1649309
- Journal Information:
- Environmental Science and Technology, Vol. 53, Issue 24; ISSN 0013-936X
- Publisher:
- American Chemical Society (ACS)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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