Genotypic and phenotypic characterization of hydrogenotrophic denitrifiers
Clara Duffner1,2, Susanne Kublik2, Bärbel Fösel2
1Chair of Soil Science, TUM School of Life Sciences Weihenstephan, Technical University of Munich, Freising, Germany.
Environmental Microbiology
|February 2, 2022
Summary
Hydrogen-driven denitrification in aquifers can produce harmful nitrite and nitrous oxide. Genomic and kinetic studies revealed that reductase activity and gene regulation influence intermediate accumulation, suggesting strategies to optimize this crucial bioremediation process.
Area of Science:
- Environmental microbiology
- Bioremediation
- Biogeochemical cycles
Background:
- Litho-autotrophic denitrification using hydrogen is a promising aquifer remediation strategy for nitrate (NO3-) removal.
- This process can lead to the accumulation of cytotoxic nitrite (NO2-) and the greenhouse gas nitrous oxide (N2O).
- Understanding the factors controlling these intermediates is crucial for optimizing denitrification efficiency and safety.
Purpose of the Study:
- To investigate the genomic composition, gene regulation, and enzyme kinetics of hydrogenotrophic denitrifiers.
- To determine the causes of high nitrite (NO2-) and nitrous oxide (N2O) accumulation during aquifer denitrification.
- To assess the influence of microbial genetics and enzyme kinetics on denitrification pathway intermediates.
Main Methods:
- Isolation of hydrogenotrophic denitrifiers from a polluted aquifer.
- Whole-genome sequencing and phenotypic investigation of isolated strains.
- Assessment of denitrification intermediate kinetics (NO2-, NO, N2O, N2, O2) under varying electron acceptor conditions.
Main Results:
- Isolates belonged to genera related to *Dechloromonas*, *Ferribacterium*, and *Hydrogenophaga*, possessing complete denitrification pathways.
- High NO2- accumulation correlated with specific reductase kinetics, with *narG*-containing strains favoring NO3- reduction and *napA*-containing strains showing concurrent reduction of intermediates.
- The denitrification regulator RegAB in *napA* strains may reduce intermediate buildup, while high N2O accumulation occurred during the transition phase, suggesting delayed N2O reductase expression.
Conclusions:
- Microbial genomics and enzyme kinetics significantly influence intermediate accumulation during hydrogen-driven denitrification.
- The presence of the RegAB regulator and specific reductase pathways can mitigate the buildup of toxic NO2-.
- Delayed N2O reductase expression during the transition to denitrification is a key factor for N2O accumulation.
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