A single bacterial strain, *Sinorhizobium meliloti* WSM1022, can recruit a custom team of other microbes around legume roots to supply the plant with nitrogen—but this teamwork may fall apart under drought or changing nitrogen levels. This matters because agriculture faces a double bind: it must produce more food while using less synthetic nitrogen fertiliser, which is energy-intensive to manufacture and pollutes waterways. Previous attempts to apply single beneficial microbes to crops have largely failed in real fields, because the microbes cannot survive or perform as they do in the lab. The researchers have already shown that WSM1022 not only fixes nitrogen itself but also shapes a "N-biome"—a mini-community of other bacteria that boosts nitrogen fixation and provides additional benefits to the plant. The gap is whether this N-biome remains stable and functional when the plant faces drought or variable nitrogen availability. If the N-biome proves robust under stress, it could be developed into a biological product for farmers. Legume crops such as peas, beans, and clover could rely on this microbial team rather than synthetic fertiliser, reducing agriculture’s carbon footprint and making food production more resilient to climate change. The project also uses genome-wide association studies to identify which plant genes help establish the N-biome under drought, opening the door to breeding crops that actively recruit and support their own nitrogen-supplying microbiome.
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Agricultural plant production is a resource-intensive process that is increasingly challenged by changing climates. Solutions for a more sustainable and resilient way of plant production are therefore urgently required. Plant roots are a habitat for highly complex microbial communities and plants benefit from intimate interactions with these microbes. In addition to mediating tolerance against climate stress, some microbes can improve plant nutrition. While it indicates the value of microbes to sustain plant production, field applications with individual beneficial microbes often do not meet their beneficial activities observed under lab conditions. In previous joint studies, we identified the nodulating bacteria S. meliloti WSM1022 as highly efficient in supplying the legume Medicago truncatula with nitrogen (N) in different soil types. Moreover, we found that WSM1022 can modulate the root microbiome to form a mini-microbiome that together with WSM1022 that we defined as the N-biome. In addition to supporting N-fixation the N-biome appears to transfer additional benefits to M. truncatula. In this project we aim to evaluate the robustness of the N-biome-M. truncatulasymbiosis under different N regimes and drought as prevalent climate stress using greenhouse settings with field soil. We will quantify the efficiency of nodulation and N-fixation, plant growth and development as well as the expression of symbiosis and drought stress marker genes to evaluate functional robustness of the N-biome-M. truncatula symbiosis. We will further apply genome-wide association studies to identify genetic traits of M. truncatula that support N-biome establishment under drought stress. All experiments are paralleled by root microbiome analyses to determine N-biome integrity or even its functional expansion by recruiting additional beneficial microbes under these changing environments. Our project thus aims to develop the N-biome as a biological entity for future field applications.
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