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DNRA and Denitrification Coexist over a Broad Range of Acetate/N-NO 3 − Ratios, in a Chemostat Enrichment Culture

View Article: PubMed Central - PubMed

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.

No MeSH data available.


Calculated change in residual nitrate (solid line) and acetate (dotted line) concentrations for change of influent Ac/N ratio in a chemostat enrichment culture. (A), Denitrification only. (B), DNRA only. (C), Denitrification and DNRA.
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Figure 5: Calculated change in residual nitrate (solid line) and acetate (dotted line) concentrations for change of influent Ac/N ratio in a chemostat enrichment culture. (A), Denitrification only. (B), DNRA only. (C), Denitrification and DNRA.

Mentions: For a remarkably wide range of Ac/N ratios no nitrate or acetate could be detected in the effluent and both nitrate reduction processes co-existed. In case of one conversion, with one electron donor and one electron acceptor, e.g., when only denitrification or DNRA occurs, this dual limitation range is expected to be very narrow. This is shown in Figures 5A,B, where the effluent concentrations of acetate and nitrate are calculated assuming that either DNRA or denitrification occurs. Furthermore, these graphs (Figures 5A,B) show that the Ac/N ratio where both carbon and nitrogen limitation occur is strongly different for denitrification (Ac/N = 0.89) and DNRA (Ac/N = 1.36). This is due to the difference in the number of electrons transferred per unit of nitrate converted. This difference in stoichiometry between both processes prompts the double limitation for nitrate and acetate and co-occurrence of DNRA and denitrification over a broad range of Ac/N ratios.


DNRA and Denitrification Coexist over a Broad Range of Acetate/N-NO 3 − Ratios, in a Chemostat Enrichment Culture
Calculated change in residual nitrate (solid line) and acetate (dotted line) concentrations for change of influent Ac/N ratio in a chemostat enrichment culture. (A), Denitrification only. (B), DNRA only. (C), Denitrification and DNRA.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121219&req=5

Figure 5: Calculated change in residual nitrate (solid line) and acetate (dotted line) concentrations for change of influent Ac/N ratio in a chemostat enrichment culture. (A), Denitrification only. (B), DNRA only. (C), Denitrification and DNRA.
Mentions: For a remarkably wide range of Ac/N ratios no nitrate or acetate could be detected in the effluent and both nitrate reduction processes co-existed. In case of one conversion, with one electron donor and one electron acceptor, e.g., when only denitrification or DNRA occurs, this dual limitation range is expected to be very narrow. This is shown in Figures 5A,B, where the effluent concentrations of acetate and nitrate are calculated assuming that either DNRA or denitrification occurs. Furthermore, these graphs (Figures 5A,B) show that the Ac/N ratio where both carbon and nitrogen limitation occur is strongly different for denitrification (Ac/N = 0.89) and DNRA (Ac/N = 1.36). This is due to the difference in the number of electrons transferred per unit of nitrate converted. This difference in stoichiometry between both processes prompts the double limitation for nitrate and acetate and co-occurrence of DNRA and denitrification over a broad range of Ac/N ratios.

View Article: PubMed Central - PubMed

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.

No MeSH data available.