Molasses-amended siderophore biofertilizer reshapes the rhizosphere microbiome, promotes growth and reduces lipid peroxidation in Ocimum basilicum L

Abstract

Introduction Siderophore-producing bacteria and their metabolites represent promising components of next-generation biofertilizers, yet their effects on plant physiology and soil microbiome structure remain insufficiently understood. Methods We developed a liquid biofertilizer based on siderophores and siderophore-accompanying metabolites (SSAM) produced by Pseudomonas sp. ANT_H12B and formulated with molasses as an organic carrier. Its effects on sweet basil (Ocimum basilicum L.) were evaluated by assessing plant growth, photosynthetic performance, lipid peroxidation, elemental composition, soil enzyme activities, and bacterial community structure using full-length 16S rRNA nanopore sequencing. Results The combined SSAM+molasses formulation significantly enhanced plant growth, increasing leaf dry biomass by nearly 180%, leaf number by more than 300%, and stem length by approximately 40–50% compared with untreated plants. Improved plant performance was accompanied by enhanced photosynthetic efficiency (Fv/FM) and a marked reduction in oxidative stress, as reflected by nearly 50% lower malondialdehyde (MDA) content compared with the molasses-only treatment. Although elemental analysis revealed no major disturbances in plant nutrient balance among treatments, soil supplementation with the combined formulation strongly affected rhizosphere functioning and microbiome composition. In particular, the SSAM+molasses treatment coincided with approximately 35–50% higher β-glucosidase and dehydrogenase activities and clear shifts in microbial community structure. Discussion These findings suggest that molasses-enriched siderophore metabolites may act as effective biostimulants by promoting plant growth and mitigating oxidative stress, partly through modulation of rhizosphere microbiome structure and function.