Genomic and biological characterization of Streptomyces strains isolated from barley

Background: Plant microbiota has been the subject of a great deal of research in recent years. In particular, the microbiota of cereals is increasingly being studied in order to identify bacteria that can improve plant health and growth. Barley is the world's fourth most important cereal crop in terms of agricultural production. Intensive cultivation of this plant requires the use of chemical inputs to compensate nutrients deficiencies in agricultural soils and to limit pathogens. Isolating and using bacteria that can increase the bioavailability of soil nutrients and inhibit the development of plant pathogens could ultimately limit the use of these chemicals. In this study, we isolated three bacteria from the barley microbiota: Streptomyces sp. GPA1, GPAT2 and GPN2. Results: These bacteria, which belong to the Streptomyces genus and are phylogenetically related, act differently on barley in hydroponic axenic conditions. Streptomyces sp. GPAT2 and GPN2 belong to the Streptomyces murinus species. Inoculation of barley with Streptomyces sp. GPAT2 led to a shorter root length after two weeks of growth, while inoculation with Streptomyces sp. GPN2 did not appear to have any effect on barley roots. Streptomyces sp. GPA1, identified as a new species, increases root growth in barley. This bacterium has various PGP effects, including phosphate and zinc solubilization and siderophore production. A metabolic study of bacterial culture also showed indole-3-acetic acid (IAA) production and excretion by Streptomyces sp. GPA1. These three Streptomyces strains also have antagonistic activities against two microorganisms inhibiting barley germination: Pseudomonas sp. MRN1 and Fusarium sp. CK. Conclusion: This study led to the characterization of three phylogenetically related bacteria with different interaction capacities with barley, showing that effect on plant is strain-specific. These results suggest that each plant line may be adapted to a particular strain of Streptomyces , and these specific interactions may result from molecular mechanisms established between the two organisms as a result of co-evolutionary processes.