Genomes of Antarctic denitrifying isolates provide insights into denitrification metabolic pathways.

Abstract

Nitrous oxide (N₂O) is a highly potent greenhouse gas (GHG), with a global warming potential approximately 300 times greater than that of carbon dioxide (CO₂). In natural environments, N₂O is produced by microorganisms through processes such as denitrification, nitrification, and dissimilatory nitrate reduction to ammonium. N₂O emissions measured in Antarctic soils affected by marine animals exhibit values comparable to those reported for highly impacted environments, including fertilized soils and livestock systems. In addition, an increased abundance of genes associated with the three N₂O production pathways has been observed in these impacted soils. However, the microorganisms responsible for N₂O emissions in these ecosystems remain poorly explored. In a previous study, 199 denitrifying bacteria were isolated from diverse Antarctic ecosystems on King George Island, all of which were capable of denitrification at 4 °C. Although most of these strains exhibited denitrifying activity, the genes responsible for this process could not be identified in the genomes of closely related species. The aim of this study was to characterize the genes involved in denitrification in these isolates. To this end, the genomes of 11 strains belonging to the genera Pseudomonas, Janthinobacterium, and Flavobacterium were sequenced and analyzed using the KEGG and NCycDB databases. The results indicated that strains of the genus Pseudomonas harbor a complete denitrification pathway, whereas Janthinobacterium strains lacked the nosZ gene, suggesting incomplete denitrification. In Flavobacterium strains, genes required for denitrification were detected, except those encoding the enzyme responsible for the first step of the process. These findings highlight the complexity of denitrification mechanisms in Antarctic bacteria and open new perspectives for understanding their role in biogeochemical cycles and greenhouse gas production.