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Fermentative Bacteria Influence the Competition between Denitrifiers and DNRA Bacteria.

Eveline M van den Berg1, Marina P Elisário1, J Gijs Kuenen1

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Summary

The ratio of lactate to nitrate influences microbial competition between denitrification and dissimilatory reduction to ammonium (DNRA). Fermentative bacteria impact substrate availability, altering nitrate reduction pathways.

Keywords:
DNRALac/N-ratiochemostatdenitrificationdissimilatory nitrate reduction

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Area of Science:

  • Biogeochemistry
  • Microbial Ecology
  • Environmental Microbiology

Background:

  • Denitrification and dissimilatory reduction to ammonium (DNRA) are key microbial processes governing nitrogen cycling.
  • The carbon source and electron donor significantly influence the competition between these two nitrate reduction pathways.

Purpose of the Study:

  • To investigate the impact of varying lactate to nitrate (Lac/N) ratios on the competition between denitrification and DNRA.
  • To elucidate the mechanistic basis of these microbial conversions under anoxic conditions.

Main Methods:

  • Utilized an open chemostat culture enriched from activated sludge.
  • Integrated results from batch tests, molecular biomass analysis, and a computational model.
  • Investigated microbial communities under strict anoxia with varying Lac/N ratios.

Main Results:

  • At high Lac/N ratios, both fermentative and respiratory DNRA occurred alongside lactate fermentation and oxidation.
  • At lower Lac/N ratios, denitrification became coupled to lactate oxidation, reducing the proportion of DNRA.
  • Identified specific bacterial groups, including *Geobacter* and *Clostridiales* members, likely responsible for DNRA and fermentation, and *Propionivibrio militaris* for denitrification.

Conclusions:

  • The substrate ratio and electron donor type critically affect the competition between DNRA and denitrification.
  • Fermentative bacteria play a key role by consuming electron donors, thereby influencing substrate availability for nitrate reducers.