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The application of bacterial bio-inputs is a very attractive alternative to the use of mineral fertilisers. In ploughed soils including a crop rotation pea, we observed an enrichment of bacterial communities with Sphingomonas (S.) sediminicola. Inoculation experiments, cytological studies, and de novo sequencing were used to investigate the beneficial role of S. sediminicola in pea. S. sediminicola is able to colonise pea plants and establish a symbiotic association that promotes plant biomass production. Sequencing of the S. sediminicola genome revealed the existence of genes involved in secretion systems, Nod factor synthesis, and nitrogenase activity. Light and electron microscopic observations allowed us to refine the different steps involved in the establishment of the symbiotic association, including the formation of infection threads, the entry of the bacteria into the root cells, and the development of differentiated bacteroids in root nodules. These results, together with phylogenetic analysis, demonstrated that S. sediminicola is a non-rhizobia that has the potential to develop a beneficial symbiotic association with a legume. Such a symbiotic association could be a promising alternative for the development of more sustainable agricultural practices, especially under reduced N fertilisation conditions.

Aphids are major pests of field crops, and their control still largely relies on chemical insecticides, which have significant ecological and health drawbacks. Recent studies suggest that plants, such as pea (Pisum sativum) can recruit beneficial bacteria in the rhizosphere potentially influencing their resilience to insect pests. However, the implications of this microbial recruitment in plant-insect interactions remain underexplored. In this study, we investigated how key rhizosphere bacteria of pea, including Rhizobium leguminosarum, S. sediminicola, and S. daechungensis, modulate pea-aphid (Acyrthosiphon pisum) interactions and affect plant productivity. We assessed both the bottom-up effects of individual and combined bacterial inoculations on plant health and aphid performance, and the top-down effects of aphid infestation on soil functionality. Our results demonstrate that inoculation with S. sediminicola and/or S. daechungensis significantly reduced aphid fecundity, while mitigating aphid-induced stress on pea plants, thereby supporting overall plant growth and productivity. Conversely, aphid infestation negatively impacted soil functionality, potentially disrupting beneficial microbial communities. These findings highlight the potential of targeted microbial recruitment as a sustainable approach to enhance plant productivity and resilience against aphid pests.