Extracellular Vesicles isolated from Streptomyces violaceoruber: an interesting natural tool for plant growth and health

Climate change and growing food demand necessitate eco-sustainable solutions to optimize resources use and reduce chemical inputs, aligning with the Farm to Fork strategy. Biofertilizers, based on Plant Growth Promoting Bacteria (PGPB), offer a promising approach. Among these, Streptomyces species show significant potential. One key mechanism may involve extracellular vesicles (EVs), nanosized structures carrying proteins, nucleic acids, and bioactive compounds. This research focuses on the isolation and characterization of EVs from Streptomyces violaceoruber, a PGPB that is a prolific source of bioactive compounds, evaluating their plant-growth promotion and stress-mitigation capabilities on Solanum lycopersicum tomato plants. EVs were isolated using sequential filtration, centrifugation, and ultracentrifugation from S. violaceoruber six-days cultures performed in liquid minimal medium. Morphological properties were analysed using transmission electron microscopy and dynamic light scattering. Molecular profiling has involved omics-based approaches (i.e. next-generation sequencing, mass spectrometry analyses), while functional assays evaluated antimicrobial activity and plant growth promotion (PGP). EVs, ranging from 100–200 nm in size, contain the whole S. violaceoruber genomic DNA. Additionally, they contain proteins as the metabolic cargo has to be characterized. Interestingly, EVs exhibited antibacterial properties and showed PGP effects on tomato seedlings. Experiments are underway to evaluate their capability to mitigate plant abiotic and biotic stresses. Therefore, this research will be able to provide further evidences on Streptomyces EVs in trans-kingdom communication (microbe-microbe and plant-microbe interactions) and to pose the basis for the development of new EV-based biofertilizers.