The hidden role of rhizospheric viruses in promoting nitrogen fixation in soils.
basic_science · Level V
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- Record sourced from PubMed, PMID 41851125.
- Also identified by DOI 10.1038/s41467-026-70744-1.
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Abstract
Biological nitrogen fixation is a cornerstone of terrestrial nitrogen cycling, traditionally attributed to bacterial nitrogenase activity. However, the potential contribution of rhizospheric viruses remains largely unexplored. Here, we reveal the global distribution of nitrogen-fixing genes, with widespread detection of nifA, nifL, nifU, and nifH in both bacteria and viruses, and identify nifU as a viral auxiliary metabolic gene (AMG). Analysis of viral communities in rhizosphere and bulk soils cultivated with cowpea showed that viral nifU expression was significantly upregulated in rhizosphere soils. Using <sup>15</sup>N₂ stable-isotope tracing and virus transplantation experiments, we demonstrate that virus-encoded nitrogen-fixing AMGs, horizontally transferred from bacteria such as Azospirillum thermophilum (70-99% homology), increased nitrogenase activity from 1.79 to 3.14 nmol C<sub>2</sub>H<sub>4</sub> g<sup>-1</sup> dry soil h<sup>-1</sup>. This enhancement was accompanied by shifts in bacterial community composition, with the relative abundance of the nitrogen-fixing genus Azotobacter reaching 90.8%. These results uncover a previously hidden role of rhizospheric viruses in promoting bacterial nitrogen fixation, suggesting that viral-mediated gene transfer could be leveraged to enhance nitrogen cycling in soils and inform sustainable soil management strategies.