Kaya, D., B.V. Kjellerup, K. Chourey, R.L. Hettich, D.M. Taggart, and F.E. Loffler.
Environmental Science & Technology 53(24):14548-14558(2019)

The effect of NH⁴⁺ availability on Dehalococcoides mccartyi (Dhc) growth and reductive dechlorination was tested on enrichment cultures derived from chlorinated ethene-impacted groundwater (PW₄) and river sediment (TC). Compared to incubations without NH⁴⁺, PW₄ cultures increased cDCE-to-ethene dechlorination rates (20.6 ± 1.6 µM Cl^-/d vs 3.8 ± 0.5 µM Clsup>-/d), and the total number of Dhc 16S rRNA gene copies ((1.8 ± 0.9)×108/mL versus (4.1 ± 0.8)×107/mL). In TC cultures, NH⁴⁺ also stimulated cDCE-to-ethene dechlorination and Dhc growth. 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. 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⁺. 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. Findings demonstrated that biostimulation with NH⁴⁺ can enhance Dhc reductive dechlorination rates but a "do nothing" approach that relies on indigenous diazotrophs can achieve similar dechlorination endpoints and avoids the potential for stalled dechlorination due to inhibitory levels of NH⁴⁺ or transformation products.