Diversity and Plant Growth-Promoting Properties of Rhodiola rosea Root Endophytic Bacteria

Plants inhabiting environments with suboptimal growth conditions often have a more pronounced capacity to attract and sustain microbial communities that improve nutrient absorption and expand abiotic stress tolerance. <i>Rhodiola rosea</i> L. is a succulent plant of the <i>Crassulaceae</i> family adapted to survive in sandy or rocky soils or dry tundra. The aim of the present study was to investigate the diversity and plant growth-stimulating potential of <i>R. rosea</i> endophytic microbiota. Metataxonomic analysis of the bacterial diversity in the rhizome of <i>R. rosea</i> revealed 108 families. Among these, three families were found exclusively in the core microbiome of 1-year-old plants, while nine families were unique to the core microbiome of mature plants grown in the field for more than 4 years. Seventy-three endophytic bacteria isolates were obtained from the rhizome of <i>R. rosea</i> plants and were assigned into 14 distinct bacterial genera of Firmicutes (26%) or Proteobacteria (74%) phyla. Screening for functional genes related to the nitrogen cycle, phosphorus mineralisation or dissolution, and traits associated with nitrogen fixation (56% of isolates), siderophore production (40%), inorganic phosphorus solubilisation (30%), and production of indole-related compounds (51%) led to the classification of the isolates into 16 distinct clusters. Co-cultivation of 45 selected isolates with germinating Arabidopsis seedlings revealed 18 and 5 isolates that resulted in more than a 20% increase in root or shoot growth, respectively. The study results established the complexity of the succulent <i>R. rosea</i> endophytic microbiome and identified isolates for potential plant growth-stimulating applications.