Biological Nitrogen Removal Database

Citrobacter sp. strain Soil_DNRA_Lac_191

• Phylum : Proteobacteria
• Class : Gammaproteobacteria
• Order :Enterobacterales
• Family : Enterobacteriaceae
• Genus : Citrobacter

Nitrate

Lactate or Glucose

Reference:Heo et al., 2020

Title:Involvement of NO3− in Ecophysiological Regulation of Dissimilatory Nitrate/Nitrite Reduction to Ammonium (DNRA) Is Implied by Physiological Characterization of Soil DNRA Bacteria Isolated via a Colorimetric Screening Method

Pubmed ID:32631862

Pubmed link:Link

Full research link:Link

Abstract: Dissimilatory nitrate/nitrite reduction to ammonium (DNRA) has recently regained attention as a nitrogen retention pathway that may potentially be harnessed to alleviate nitrogen loss resulting from denitrification. Until recently, the ecophysiology of DNRA bacteria inhabiting agricultural soils has remained largely unexplored, due to the difficulty in targeted enrichment and isolation of DNRA microorganisms. In this study, >100 DNRA bacteria were isolated from NO3−-reducing anoxic enrichment cultures established with rice paddy soils using a newly developed colorimetric screening method. Six of these isolates, each assigned to a different genus, were characterized to improve the understanding of DNRA physiology. All the isolates carried nrfA and/or nirB, and the Bacillus sp. strain possessed a clade II nosZ gene conferring the capacity for N2O reduction. A common prominent physiological feature observed in the isolates was NO2− accumulation before NH4+ production, which was further examined with Citrobacter sp. strain DNRA3 (possessing nrfA and nirB) and Enterobacter sp. strain DNRA5 (possessing only nirB). Both isolates showed inhibition of NO2−-to-NH4+ reduction at submillimolar NO3− concentrations and downregulation of nrfA or nirB transcription when NO3− was being reduced to NO2−. In batch and chemostat experiments, both isolates produced NH4+ from NO3− reduction when incubated with excess organic electron donors, while incubation with excess NO3− resulted in NO2− buildup but no substantial NH4+ production, presumably due to inhibitory NO3− concentrations. This previously overlooked link between NO3− repression of NO2−-to-NH4+ reduction and the C-to-N ratio regulation of DNRA activity may be a key mechanism underpinning denitrification-versus-DNRA competition in soil.