DNRA and Denitrification Coexist over a Broad Range of Acetate/N-NO3− Ratios, in a Chemostat Enrichment Culture

Abstract

Denitrification and dissimilatory nitrate reduction to ammonium (DNRA) compete for nitrate in natural and engineered environments. A known important factor in this microbial competition is the ratio of available electron donor and elector acceptor, here expressed as Ac/N ratio (acetate/nitrate-nitrogen). We studied the impact of the Ac/N ratio on the nitrate reduction pathways in chemostat enrichment cultures, grown on acetate mineral medium. Stepwise, conditions were changed from nitrate limitation to nitrate excess in the system by applying a variable Ac/N ratio in the feed. We observed a clear correlation between Ac/N ratio and DNRA activity and the DNRA population in our reactor. The DNRA bacteria dominated under nitrate limiting conditions in the reactor and were outcompeted by denitrifiers under limitation of acetate. Interestingly, in a broad range of Ac/N ratios a dual limitation of acetate and nitrate occurred with co-occurrence of DNRA bacteria and denitrifiers. To explain these observations, the system was described using a kinetic model. The model illustrates that the Ac/N effect and concomitant broad dual limitation range related to the difference in stoichiometry between both processes, as well as the differences in electron donor and acceptor affinities. Population analysis showed that the presumed DRNA-performing bacteria were the same under nitrate limitation and under dual limiting conditions, whereas the presumed denitrifying population changed under single and dual limitation conditions.

Role of nitrite in the competition between denitrification and DNRA in a chemostat enrichment culture

“…The ammonia production using nitrate is obtained from the model for our previous study (van den Berg et al 2016). The shown ammonia concentrations for use of nitrite are an extrapolation of the model data…”

Biological System Characterization to Address Biofouling of the 200 West Pump-and-Treat Injection Wells

“…Environmental conditions that tend to favor DNRA over denitrification include a consistent supply of OC, carbon quality (fermentable substrates), low concentrations of nitrate, high C/N ratio, high temperatures, and variable pH, nitrite, and sulfide concentrations. Moreover, DNRA populations (and activity) are generally much less sensitive to changing environmental conditions than denitrifying bacteria (Rivett et al 2008;van den Berg et al 2016). It is improbable to assume that all DNRA activity can be eliminated, but it is conceivable that conditions in the FBR biological treatment system could be effectively managed to better control nitrate attenuation pathways in favor of denitrification to prevent unwanted production of ammonia.…”

“…In actuality, complex carbon sources can decrease operational control and reproducibility of complex biological systems (like the FBR) because it encourages the growth of metabolic competitors that unpredictably change the carbon substrate profile of the system. Heterotrophic and fermentative bacteria, for example, have been shown to strongly influence NO 3 attenuation activity by quickly altering the quantity and quality of carbon supplies available for nitrate reducing bacteria (van den Berg et al 2016(van den Berg et al , 2017a. Poor growth performance of GAC samples on MicroC® 4100 has been shown prior (Morad et al 2017).…”

Fermentative Bacteria Influence the Competition between Denitrifiers and DNRA Bacteria

“…An environmental factor well-reported to direct the competition between denitrification and DNRA is the C/N ratio of available substrates (Rütting et al, 2011 ; Kraft et al, 2014 ). DNRA bacteria have a competitive advantage in nitrate limiting conditions and excess of electron donor, whereas denitrifiers are more competitive when electron donor is limiting (Kraft et al, 2014 ; van den Berg et al, 2016 ). This was shown qualitatively in both aquatic and terrestrial environments.…”

“…This was shown qualitatively in both aquatic and terrestrial environments. Lab cultures provided more insight in the mechanism of this selection by the ratio of available substrates (e.g., Tiedje et al, 1982 ; Akunna et al, 1994 ; Yoon et al, 2015 ; van den Berg et al, 2016 ). Tiedje et al ( 1982 ) proposed that DNRA could be more favorable under nitrate limiting conditions, because of the capacity of DNRA to accept eight electrons per nitrate, whereas in denitrification five electrons are accepted, even though thermodynamics suggest that the free energy change per nitrate reduced is comparable.…”