Dissimilatory nitrate reduction by a freshwater cable bacterium.
Ugo Marzocchi1,2,3, Casper Thorup4,5, Ann-Sofie Dam4,5
1Department of Chemistry, Vrije Universiteit Brussel, Brussel, Belgium. ugomar@bio.au.dk.
The ISME Journal
|July 3, 2021
Summary
Cable bacteria perform dissimilatory nitrate reduction to ammonium (DNRA), a key nitrogen cycling process. This finding reveals their significant role in marine and freshwater ecosystems.
Area of Science:
- Microbiology
- Environmental Science
- Biogeochemistry
Background:
- Cable bacteria (CB) are unique filamentous microorganisms that spatially separate redox reactions.
- Their role in the nitrogen cycle is unclear due to unknown nitrate reduction pathways.
Purpose of the Study:
- To investigate the nitrate reduction pathway in the freshwater cable bacterium Ca. Electronema sp. GS.
- To determine the impact of Ca. Electronema sp. GS on dissimilatory nitrate reduction to ammonium (DNRA).
Main Methods:
- Incubation of sediment with 15NO3- and Ca. Electronema sp. GS.
- Measurement of DNRA and nitrite production rates.
- Electric potential (EP) measurements to infer electron flux.
- Gene expression analysis of nitrate reduction pathways.
Main Results:
- Ca. Electronema sp. GS performs DNRA, increasing DNRA and nitrite production in sediments.
- Electron flux from sulfide oxidation supports CB-mediated nitrate reduction.
- Expression of the nap operon for nitrate reduction to nitrite was observed.
Conclusions:
- Ca. Electronema sp. GS contributes significantly to DNRA in freshwater environments.
- The DNRA capacity in CB was acquired through horizontal gene transfer.
- CB primarily conserve energy via sulfide oxidation, not oxidative phosphorylation.
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