Endophytic Bacillus strains enhance biomass and bioactive metabolites of Gloriosa superba

Gloriosa superba L. is an economically important medicinal plant and variation in its colchicine content may be due to associated endo- and ectophytic beneficial microbes. Among them, endophytic bacteria contribute to enhancing plant growth, induce biotic and abiotic stress tolerance, and play a significant role in secondary metabolite synthesis. In the present study, 76 native endophytic bacteria were isolated from high and low-colchicine and gloriosine-containing chemotypes of G. superba rhizome and characterized for vegetative growth enhancement and abiotic stress mitigation. The screening has resulted in the selection of 23 plant growth-promoting (PGP) bacterial endophytes with abiotic stress tolerance. Most of these isolates belong to the Bacillus genera identification based on the 16S rRNA gene. Based on the significant enhancement in maize (Zea mays L.; as model host plant) under greenhouse conditions ten efficient bacterial strains were selected. Further, three endophytic bacterial strains, NBRI HYL5 and NBRI HYL8 (high colchicine and gloriosine containing chemotype), and NBRI LYN9 (low colchicine and gloriosine containing chemotype) were selected based on the survivability and enhanced 1-aminocyclopropane-1- carboxylate (ACC) deaminase activity, phosphate solubilization, biofilm, Indole acidic acid (IAA), exopolysaccharide, and alginate production abilities under different abiotic stress conditions. Finally, a greenhouse experiment was conducted to evaluate the effect of selected bacterial endophyte inoculation in G. superba for growth enhancement and secondary metabolite content. The results showed that plants treated with NBRI HYL5 and NBRI HYL8 significantly enhanced the colchicine content (97–98 %) and gloriosine content (70–73 %), respectively as compared with control. However, inoculation of NBRI LYN9 has demonstrated significant enhancement only in gloriosine content (79 %). In addition, NBRI HYL5 and NBRI HYL8 have demonstrated significant improvement in overall vegetative growth parameters, photosynthetic pigments, and total soluble sugar content. Colonization and persistence of selected endophytic bacteria in G. superba rhizome and shoot clearly depicted the involvement not only in enhancing the vegetative growth but also in enhancing the colchicine and gloriosine content. Overall, this study presents the beneficial role of endophytic Bacillus strains in enhancing the growth of G. superba and secondary metabolite content may lead to contribute in sustainable cultivation of economically important medicinal plants.