Nitrogen is an essential building block of proteins, amino acids, and DNA. Without nitrogen, cells can’t function or reproduce. Nitrogen is abundant in the atmosphere as dinitrogen gas, but plants and animals can’t access atmospheric nitrogen. Instead, we rely on biologically available forms like ammonia and nitrate. 

Specialized microbes can transform atmospheric nitrogen into ammonia via a process called biological nitrogen fixation. Nitrogen-fixing soil bacteria have a unique protein complex, the nitrogenase complex, that facilitates this nitrogen transformation. The nitrogenase complex is activated by a group of genes known as nif genes. 

Legume plants like peanuts, peas, and beans have nitrogen-fixing bacteria in the soil zone around their roots, called the rhizosphere. The symbiotic relationship between nitrogen-fixing soil bacteria and legume plants supplies most of the biologically available nitrogen to life on Earth.

Bacteria attached to plant roots “feed” nitrogen to plants through the soil, and in turn receive organic acids for energy from plants performing photosynthesis. Source: Wikimedia Commons

However, one piece of the puzzle remains unexplored: the role of soil viruses in these nitrogen transformations, referred to as the nitrogen cycle. Viruses are microscopic particles made up of genetic material and proteins, but they can’t reproduce without a host cell. Scientists consider viruses to be biological entities that are halfway between living and non-living.

To reproduce, viruses contact a host cell and inject their genetic material into it. The virus’s genetic material takes over the host cell’s genome and forces the cell to produce proteins that assemble into new viruses. As new viruses are created, they can incorporate genes from the host cell into their own genetic material. Genes that are transferred from a host cell to a virus are known as auxiliary metabolic genes (AMGs). Viruses can carry AMGs and pass them to other hosts or use them to increase their own ecological fitness. 

Scientists from China, Spain, and the Czech Republic set out to investigate whether viruses from legume roots could increase local soil nitrogen fixation by expressing nif AMGs or by transferring nif genes to other bacteria. First, they determined the global distribution of viral nitrogen-fixing genes by analyzing about 8.6 million viral genomes from the Integrated Microbial Genomes/Virus database. They looked for the DNA sequences of known nitrogen-fixing genes and the locations where the viruses were sampled. They found that only 0.003% of the viruses in the database had at least 1 nitrogen-fixing gene, but they clustered in the same locations as nitrogen-fixing bacteria. 

The team also found 3 types of viruses that most commonly carried nitrogen-fixing genes: Kyanoviridae, Nudiviridae, and Bronfenbrennervirinae. Kyanoviridae viruses carried a nif gene called nifU. The researchers used a computer program called DRAM-v to confirm that nifU was a fully functional gene and a real tool that viruses could use. 

Next, the team collected soil samples from a cowpea field in Nanjing, China, to test whether the cowpea roots influenced the abundance of viruses using nitrogen-fixing genes. They collected soil from the cowpea rhizospheres and soil away from the plants. They analyzed both viral and bacterial RNA in the soil samples to identify active genes, using a sequencing process called metatranscriptomics. They found that the viral nifU gene was actively expressed in the cowpea rhizosphere samples more than in the non-crop soil. Although about 96% of nifU genes were being expressed by bacteria, viruses contributed about 4%. 

The researchers then assessed whether rhizospheric viruses changed the amount of nitrogen being fixed in these soils. They set up small, enclosed containers of sterile soil and added either bacteria or a mixture of bacteria and viruses extracted from the cowpea rhizospheres. They found that soil with viruses had higher total nitrogen (36 milligrams per kilogram, or mg/kg) than soil without viruses (17 mg/kg). 

Finally, they adjusted the air in each container to have a different form of dinitrogen gas. Atoms of the same element that have different atomic masses are known as isotopes. Nitrogen has 2 stable isotopes: lighter nitrogen-14 and heavier nitrogen-15. Bacteria or viruses that fix nitrogen at natural isotope abundances will take up nitrogen-14. But scientists can track who in the population fixes nitrogen by adding nitrogen-15 to the air, a process called nitrogen-15 stable isotope probing. Nitrogen-fixers will incorporate the heavy nitrogen-15 into their biomass over time and increase their weight, allowing researchers to separate and identify them.

The team grew the bacteria and viruses with nitrogen-15 for 35 days, then used stable isotope probing to separate the nitrogen fixers. They detected viral nifU AMGs among the heavier biomass, confirming that rhizospheric viruses were fixing nitrogen. 

The team concluded that rhizospheric viruses and the viral nifU AMG can increase nitrogen fixation in cowpea soils. The team suggested that although viruses with nitrogen-fixing genes are rare, they can influence the soil nitrogen cycle. They recommended that future researchers further test the contribution of viral nifU genes to plant nitrogen fixation with controlled infection experiments.

The post Viruses help plants obtain nitrogen appeared first on Sciworthy.

In a groundbreaking revelation that could reshape our understanding of plant-microbe interactions and agricultural biotechnology, researchers have unveiled a novel chemical communication mechanism between rice roots and beneficial soil bacteria. This newly discovered pathway centers on the secretion of heptadecanoic acid, a specific fatty acid, which effectively recruits Bacillus species to the rhizosphere, the densely populated soil region surrounding plant roots. Such a mechanism not only highlights the intricate biochemical dialogues that underpin plant-microbe symbioses but also opens promising avenues for sustainable crop management through microbiome engineering.

Rice, a staple food that sustains more than half of the world’s population, has long been studied for its interactions with the soil ecosystem. The rhizosphere harbors myriad microbial communities, some of which promote plant health by enhancing nutrient acquisition, defending against pathogens, or improving stress tolerance. Identifying the exact signals that facilitate recruitment of beneficial bacteria has presented a considerable scientific challenge. The recent study by Zeng, Wen, Zhao, and colleagues provides essential insights and fills a critical gap by pinpointing heptadecanoic acid as a chemical attractant secreted by rice roots, which acts as a molecular beacon for Bacillus.

Heptadecanoic acid, also known as margaric acid, is a saturated fatty acid containing 17 carbon atoms. Traditionally, plant root exudates—complex mixtures of organic acids, sugars, amino acids, and secondary metabolites—have been observed to influence microbial colonization, but the specific involvement of fatty acids as signals was less appreciated. The team’s meticulous biochemical analyses have now elucidated that rice roots not only exude heptadecanoic acid but do so strategically when recruiting beneficial Bacillus species. This revelation signifies a refined understanding of the selective microbial recruitment strategies employed by plants.

The team’s research employed an array of advanced techniques—ranging from root exudate profiling through gas chromatography-mass spectrometry (GC-MS) to microbial chemotaxis assays—to validate that Bacillus species detect and are attracted to gradients of heptadecanoic acid in the rhizosphere. Importantly, not all soil microbes respond equivalently, underscoring the specificity of this fatty acid signal. Functional studies further demonstrated that disrupting rice root production of heptadecanoic acid diminished Bacillus colonization, which correspondingly weakened the plant’s resistance to common soil-borne pathogens.

Understanding the biochemical basis for such recruitment enables scientists to rethink approaches to crop protection and enhancement. Bacillus species are well-known for their plant growth-promoting traits, including production of antimicrobial compounds, enhancement of nutrient solubilization, and induction of systemic resistance in plants. By harnessing the heptadecanoic acid signaling pathway, it is conceivable that agricultural inoculants could be optimized to improve colonization efficiency and consistency in field conditions, potentially reducing the need for chemical pesticides and fertilizers.

This molecular dialogue highlights a sophisticated communication network where plants actively shape their microbial environment. The discovery that a fatty acid functions not merely as a structural or energy-storage molecule but as a signaling compound redefines our conception of root exudate complexity. Moreover, heptadecanoic acid’s hydrophobic nature prompts questions about its diffusion dynamics in soil and the mechanisms by which Bacillus receptors detect it. Future exploration into bacterial chemoreceptors and downstream signaling pathways activated by this molecule could illuminate novel targets for microbiome manipulation.

Beyond direct agricultural implications, this finding resonates with broader ecological principles. The soil microbiome’s composition significantly influences plant community dynamics, ecosystem productivity, and resilience to environmental stresses. By uncovering a precise mediator of microbe recruitment, the work by Zeng and colleagues contributes to the fundamental ecological theory of plant-soil feedback loops, suggesting that plants possess active biochemical agency in curating their microbial consortia.

Interestingly, the secretion of heptadecanoic acid is not constant but modulated by environmental cues and plant developmental stages, emphasizing the dynamic nature of root exudation profiles. This temporal regulation indicates that plants might selectively recruit beneficial microbes in response to specific physiological needs or external threats, adding an adaptive dimension to this interaction. Understanding these controls could inform timing strategies for microbial inoculant application in agriculture to coincide with natural recruitment periods.

The authors also raise intriguing evolutionary considerations. The conserved ability among rice varieties to secrete heptadecanoic acid suggests selective pressure favoring plants capable of enlisting Bacillus partners. Parallel studies on other cereal crops could reveal whether this fatty acid signaling is a widespread mechanism or unique to rice. Such comparative analyses across plant taxa may unearth a broader family of fatty acid signals mediating symbioses and expand the toolkit for synthetic microbiome engineering.

This pioneering investigation underscores the necessity of interdisciplinary approaches combining plant biology, microbiology, analytical chemistry, and ecology to fully decipher plant-microbe interactions. It leverages cutting-edge omics technologies and bioinformatics pipelines to characterize metabolite profiles and microbial responses, illustrating the power of integrative science. The robust experimental design and reproducible methodologies set a new benchmark for future studies aiming to parse root exudate signaling.

As the global agricultural sector grapples with the challenges of increasing food production sustainably on finite arable land under climate change pressures, the discovery of a natural plant mechanism to recruit growth-promoting and protective microbes represents a potentially transformative tool. Strategies informed by such foundational knowledge could reduce reliance on synthetic inputs, lower environmental footprints, and enhance crop resilience, aligning with ambitious global sustainability goals.

In conclusion, the identification of heptadecanoic acid as a pivotal signaling molecule secreted by rice roots to attract beneficial Bacillus species marks an exciting advance in the field of plant-microbe research. It unravels a previously unrecognized layer of biochemical communication with profound implications for agriculture and ecology. Continued investigation into the molecular details, environmental regulation, and cross-species relevance of this signaling mechanism promises to unlock innovative avenues for crop improvement and sustainable farming practices worldwide.

Subject of Research: Plant-microbe interactions focusing on the biochemical signaling between rice roots and Bacillus species mediated by heptadecanoic acid secretion.

Article Title: Author Correction: Rice roots recruit Bacillus via the secretion of heptadecanoic acid.

Article References: Zeng, J., Wen, T., Zhao, J. et al. Author Correction: Rice roots recruit Bacillus via the secretion of heptadecanoic acid. Nat. Plants (2026). https://doi.org/10.1038/s41477-026-02341-5

Image Credits: AI Generated