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IMPACT OF FIXED NITROGEN AVAILABILITY ON DEHALOCOCCOIDES MCCARTYI REDUCTIVE DECHLORINATION ACTIVITY
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.



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