Legume–Rhizobium Symbiosis and Beyond: Producing Synthetic Communities for Increasing Crop Production Under Climate Change Challenges

Rhizobia are a polyphyletic group of soil bacteria, belonging to alpha- and betaproteobacteria classes, able to colonize the rhizosphere and endosphere of plants and form symbiotic associations with legumes. The rhizobia–legume plant symbiotic interaction is a pivotal part of the input of fixed nitrogen in the agroecosystems. However, rhizobia are only a component of the plant microbiome, which is helping the plant cope with environmental stresses. The application of rhizobia as bioinoculants can then be improved by the creation of synthetic microbial communities, which include rhizobia and other plant growth-promoting bacteria and fungi. The creation of these synthetic communities is challenging since the single members should synergistically cooperate in their effects on the host plant. Systems biology can help to address the rational design of synthetic communities by providing predictions and testable models of interactions among the members of the community and the plant. Here, we will review the most recent advances in the creation of synthetic communities to increase symbiotic nitrogen fixation under climate change scenarios, such as drought and excess soil salinity.