Rhizosphere Bacillus proteolyticus Strain Enhances the Eleutherococcus senticosus (Rupr. & Maxim.) Maxim. Growth in Roots and Soil Nutrient Status While Enriching the Plant-Beneficial Bacteria in Rhizosphere

This study aimed to investigate the promoting mechanisms of <i>Bacillus proteolyticus (B. proteolyticus)</i> on <i>Eleutherococcus senticosus</i> (Rupr. and Maxim.) Maxim. (<i>therm E. senticosus</i>) root development. Using <i>therm E. senticosus</i> seeds as experimental material, soil was drenched with <i>B. proteolyticus</i> suspensions at different concentrations <i>v/v</i> (water, 25%; 50%; 75%, and 100%). The results showed that the germination rate, root tip number (52 ± 2.97), total root length (23.7 ± 0.46 cm), and total root volume (57.36 ± 1.64 mm³) exhibited an initial increase, then a decrease after <i>B. proteolyticus</i> treatment (<i>p</i> < 0.05). Principal component analysis (PCA) indicated that the soil of <i>B. proteolyticus</i> at a 50% concentration was conducive to seed germination. Compared with CK, GC-MS analysis revealed that 16 differential primary metabolites were screened, primarily enriched in galactose metabolism, starch and sucrose metabolism, and TCA cycle pathways after 50% <i>B. proteolyticus</i> treatment. LC-MS analysis revealed that the contents of six main medicinal components were higher than those of CK, with the content of eleutheroside E being 2.62 times greater. In rhizosphere soil, the contents of NO₃^--N and NH₄⁺-N were promoted, and the abundance of <i>Gemmatimonadetes</i> was increased in bacterial communities. Correlation analysis revealed significant correlations between the abundance of <i>Gemmatimonadetes</i> and the contents of NO₃^--N and NH₄⁺-N, as well as between total root length and D-galactose content, suggesting that these relationships may contribute to the root growth. Therefore, the soil of <i>B. proteolyticus</i> at a 50% concentration could enhance both the biomass and medicinal value of cultivated <i>therm E. senticosus</i>. This study provided novel insight that <i>B. proteolyticus</i> would be expected to be developed as an effective microbial preparation, offering a sustainable strategy for its agricultural production.