The many faces of nitrate ammonifying bacteria – Unraveling their role in nitrogen retention and loss, and nitrous oxide emissions in terrestrial ecosystems

Microbial nitrate respiration through nitrate reduction to ammonium leads to nitrogen (N) retention in soil, while nitrate respiration via denitrification causes gaseous N loss, including the greenhouse gas nitrous oxide.

However, our recent analysis of known nitrate ammonifiers shows that nearly 50% also carry one or several denitrification genes, suggesting they play a more complex role in N cycling than previously thought.

The aim is to assess the role of nitrate ammonifiers in the terrestrial N cycle by deciphering differences in the ecology between those only capable of reducing nitrate to ammonium and those that also denitrify and what this means for the fate of nitrate. The microorganisms performing nitrate ammonification in soil are largely overlooked with few soil representatives.

A better understanding of denitrification among soil-borne nitrate ammonifiers and factors governing the distribution of ammonifier-only and ammonifier-denitrifiers with different repertoires of denitrification genes is critical for a mechanistic understanding of what controls N retention and loss in terrestrial ecosystems, and the role of nitrate ammonifiers for climate regulation.

This project combines comparative genomics with experimental work based on soil microcosms and the use of metagenomics and stable isotopes, and isolation and characterization of dual-pathway nitrate ammonifiers to provide novel insights into the ecology of nitrate ammonifiers at the community and species level.