Molecular and functional characterization of plant growth-promoting bacterial endophytes from Curcuma longa rhizomes for microbiome-based agricultural solutions

Curcuma longa (turmeric) is a globally significant medicinal and culinary crop, prized for its bioactive rhizomes rich in pharmacologically active compounds. Despite its importance, the rhizome-associated microbiome, particularly the endophytic bacterial species, remains poorly characterized in tropical soils. These endophytes may play critical roles in enhancing rhizome bioactivity and plant resilience to stresses that commonly limit productivity. Although endophyte-derived microbial inoculants have garnered increasing attention, their success has often been constrained by the use of non-native strains poorly adapted to local agroecological conditions. Here, we characterize and identify isolated native endophytic bacteria from turmeric rhizomes with the potential to enhance rhizome bioactivity under stressed conditions. Six potential bacterial strains were characterized and identified via full-length 16S rDNA sequencing as Pseudomonas putida (CaTb1), Priestia megaterium (CeDs1), Brevundimonas bullata (CeNk1), Pseudomonas syringae (KbNk1 and GlNk1), and Leucobacter aridicollis (CeBe1). These bacterial strains exhibited tolerance to high salinity (15% NaCl), acidity (pH 4), and aluminum toxicity (100 mM Al³⁺). All strains produced 1-aminocyclopropane-1-carboxylate (ACC) deaminase and ammonia, while phosphorus solubilization was observed only in Pseudomonas species. Indole-3-acetic acid (IAA) was produced by P. syringae and L. aridicollis. All strains expressed catalase, urease, gelatinase, and most produced protease, with cellulase and amylase production seen in select strains. Additionally, all isolates demonstrated arginine and ornithine decarboxylase activities, indicating biostimulant potential. Given these characteristics, the selected endophytes—excluding the pathogenic P. syringae —represent promising candidates for development of microbiome-based products as biofertilizers/biocontrol agents to sustainably boost plant bioactivity, production, and stress resilience in tropical agricultural systems.