Isolation and Characterization of Multifunctional Seed-Borne Endophytic Bacterium Lysinibacillus sphaericus YEBEVIA for Enhancing Maize Growth

Abstract

The endosphere biology attracts increasing interest from researchers seeking to understand plant-microbe synergism and the bio-efficacy of microbial inoculants in enhancing plant growth and soil health. This study was designed to isolate and identify a novel seed-borne endophytic Lysinibacillus sphaericus YEBEVIA with plant growth-promoting capabilities and bioinoculation potential. Morphological assessment revealed that isolate D3 was a Gram-positive, rod-shaped bacterium with a large cell size and undulated colony margins. All the isolates fermented glucose, fructose, sucrose, and maltose, producing only acid from lactose. PGP screening demonstrated that all isolates exhibited beneficial traits, although at varying intensities. Lysinibacillus sphaericus YEBEVIA displayed remarkable zinc-solubilizing ability (3.0 cm), siderophore production (2.5 cm), and high HCN activity (2.87 µg/mL). Phosphate solubilization (17.46 µg/mL) and IAA production (14.26 µg/mL) were also notably high in L. sphaericus YEBEVIA. Heavy-metal tolerance assays revealed that L. sphaericus YEBEVIA responded positively to increasing concentrations of zinc and lead, with the highest growth observed at 2 g supplementation. Enhanced tolerance to chromium was also recorded, whereas cadmium showed no significant effect compared with the control. Minimum inhibitory concentration (MIC) effects were observed only with lead sulphate, producing inhibitory zones of 5.1 cm, 2.5 cm, and 6.8 cm. Bioinoculation studies showed significant improvements in maize growth. Under field conditions, inoculated plants developed 13 leaves, 41 roots, and a fresh weight of 256.9 g, while greenhouse trials produced comparable enhancements. These findings highlight the strong potential of L. sphaericus YEBEVIA as a biofertilizer for sustainable crop improvement.