The complex microbiota of Anadenanthera colubrina seed endosphere and its plant-growth promoting potential.

In this work, we aimed to investigate the bacterial microbiota of the Anadenanthera colubrina seed endosphere, with special focus to the characterization of beneficial traits and to the colonization pattern by coupling for the first time cultivation-dependent and -independent analyses, functional tests and microscopical investigation. We isolated several Methylobacterium and Staphylococcus spp., exhibiting several plant growth promotion and antimicrobial activities. Interestingly, the two taxonomic groups showed complementary traits, which supports a functional selection for these genera. Both genera were detected by high throughput sequencing of 16S rRNA gene from total seed DNA, together with further taxa, some of which (Friedmaniella, Bifidobacterium, Delftia, Anaerococcus and Actinomyces) appeared for the first time as seed endophytes. We were able to visualize bacterial cells and micro-colonies in seed cryosections, by fluorescence in situ hybridization coupled with confocal laser scanning microscopy (FISH-CLSM). Alphaproteobacteria, Firmicutes and other bacteria, were localized in intercellular spaces and transport vessels of the seed endosphere, suggesting acquisition by endophytic translocation. Our work adds new information to shed light onto the diversity, functions and colonization pattern of the seed endophytic microbiota, and confirms the importance of seed-associated endophytes as potentially beneficial plant partners.