Dissimilatory Nitrate Reduction to Ammonia DNRA

FIGURE 8.42 Relationship between electron donor-to-electron acceptor ratio and denitrification and dissimilatory nitrate redaction to ammonia (Tiedje, 1988). 

---

FIGURE 8.48 Effect of sediment depth on partitioning of nitrate reductive processes of denitrification, dissimilatory nitrate reduction to ammonia (DNRA), and assimilatory nitrate reduction (ANR). Each value represents the mean of six relications (D Angelo and Reddy, 1993). 

Dissimilatory reduction of nitrate to ammonia is performed by obligate and facultative anaerobes with fermentative metabolism, including Clostridium and Bacillus species (Tiedje, 1988). These organisms, in contrast to denitrifiers, usually do not rely on nitrate as electron acceptor. Therefore, DNRA involves 8e transfer as compared to 5e transfer for denitrification, suggesting that more organic substrate can be potentially degraded by DNRA. However, nitrate availability under DNRA conditions is usually very low because much of the nitrate formed during nitrification under aerobic conditions is rapidly consumed by denitrifiers in adjacent anaerobic environments. 

---