Four Newly Identified Endophytic Bacillus megaterium Strains with Biofertilizer Potential for Enhancing Maize Growth and Productivity

Intensive maize farming in tropical regions has led to increasing reliance on chemical fertilizers, which negatively impact soil fertility and sustainability. To develop more eco-friendly alternatives, this study aimed to isolate and evaluate indigenous Bacillus megaterium strains with plant growth-promoting potential from maize roots grown in high-input fields of An Giang Province, Vietnam. Ten endophytic bacterial isolates were initially screened based on morphological and biochemical traits. Four promising strains of Bacillus megaterium KL-197, KSW-114, ROA 024, and KSW-113 were identified via 16S rRNA sequencing and phylogenetic analysis. These strains were further tested for nitrogenase activity using the acetylene reduction assay and for their ability to tolerate varying temperatures and salt concentrations. High nitrogen-fixing potential and ammonia production were observed, particularly in strains ROA 024 and KSW-113. Field experiments were conducted using a randomized block design with 5 treatments (4 bacterial strains and a control) to assess effects on maize growth, yield, and seed quality. Inoculation with all 4 strains significantly improved plant height, chlorophyll content, and biomass. Strains ROA 024 and KSW-113 outperformed others, resulting in increased ear length, seed number, 1000-grain weight, and fresh ear yield achieving up to a 12% yield increase over the control. Protein content in maize grains also improved with inoculation, while lipid content remained unaffected. These findings demonstrate that the 4 newly identified native Bacillus megaterium strains, especially ROA 024 and KSW-113, possess strong nitrogen-fixing and growth-promoting capabilities under field conditions. The study highlights the potential application of these strains in biofertilizer development, offering a sustainable solution to enhance maize productivity while reducing dependence on synthetic nitrogen inputs. HIGHLIGHTS Four novel Bacillus megaterium strains were isolated and identified from maize roots in intensive farming areas of Vietnam. The selected strains exhibited high nitrogenase activity and ammonia production, with strong thermal and salt tolerance. Field experiments showed that Bacillus megaterium ROA 024 and KSW-113 significantly increased maize yield by up to 12% over uninoculated controls. Inoculated plants demonstrated improved agronomic traits and grain quality, including higher protein content and biomass accumulation. The study highlights the potential of indigenous Bacillus megaterium strains as biofertilizer candidates for sustainable maize production. GRAPHICAL ABSTRACT