Biogeographical distribution of dissimilatory nitrate reduction to ammonium (DNRA) bacteria in wetland ecosystems around the world

Nitrate (NO3−) is the second preferred terminal electron acceptor after oxygen (O2), as it plays an essential role as the main electron acceptor for respiration under oxygen-depleted conditions. Dissimilatory nitrate reduction to ammonium (DNRA) is an increasingly important process of microbial-driven nitrate reduction in wetland ecosystems, making it necessary to study the biogeographical distribution and structure of the DNRA community, and to identify the factors governing DNRA in global wetlands. We collected samples from 15 wetland sites around the world and used qPCR assay analysis to quantify the DNRA functional gene nrfA. High-throughput sequencing was conducted to analyze the microbial diversity and community structure of DNRA bacteria. The most connected genera were derived from molecular ecological network analysis. Principal coordinates analysis (PCoA), redundancy analysis (RDA), and Pearson’s correlation analysis were used to explore the relationship between microbial structure and environmental factors. The environmental conditions of the wetlands varied largely with the latitude. At the phylum level, Proteobacteria was dominant, and Anaerolinea was the key genus. Pearson’s correlation analysis also illustrated that the annual average temperature, as a factor of latitude, most significantly affected DNRA abundance, followed by total organic matter (TOM) and C/N ratio. For the first time, we summarized the characteristics of DNRA bacteria at the molecular level, along with the influencing factors, in wetlands with a wide biogeographical distribution. This study provides a scientific foundation for the future study of DNRA bacteria in wetlands around the world.