Isolation, Molecular Identification and Plant Growth-Promoting Potential of Rhizome-Associated Endophytic Bacteria from Curcuma caesia Roxb.

Abstract

Curcuma caesia Roxb. (black turmeric) is an important medicinal plant belonging to the family Zingiberaceae and is valued for its diverse therapeutic properties. In addition to its rich phytochemical composition, the plant harbours diverse endophytic microorganisms that colonise internal tissues without causing disease symptoms. Among these, bacterial endophytes contribute significantly to plant growth promotion, nutrient mobilisation, stress tolerance, biological control, and the production of bioactive compounds. However, limited information is available on the cultivable bacterial endophytes associated with C. caesia and their functional potential. Therefore, the present study aimed to isolate, molecularly identify, and evaluate the plant growth-promoting potential of rhizome-associated bacterial endophytes from C. caesia. Healthy rhizomes were surface-sterilised to eliminate epiphytic microorganisms and subjected to aseptic isolation procedures using nutrient agar medium. Three morphologically distinct bacterial isolates were obtained, purified, and characterised on the basis of their cultural and morphological features. Genomic DNA was extracted from the purified isolates, and molecular identification was performed through amplification and sequencing of the 16S rRNA gene, followed by comparative analysis using the NCBI GenBank database. The isolates were identified as Enterobacter hormaechei, Bacillus flexus, and Bacillus amyloliquefaciens, with high sequence similarity to their respective reference strains. The identified isolates were further evaluated for plant growth-promoting traits, including indole-3-acetic acid (IAA) production, phosphate solubilisation, ammonia production, and hydrogen cyanide (HCN) production. All isolates exhibited the assessed plant growth-promoting characteristics, indicating their potential as beneficial microbial resources. The findings demonstrate that C. caesia harbours diverse cultivable bacterial endophytes of ecological and biotechnological importance. These endophytic bacteria may serve as potential candidates for the development of microbial inoculants, sustainable agricultural practices, extracellular enzyme production, and bioactive metabolite exploration. The present study provides baseline information on the bacterial endophytic diversity of C. caesia and highlights its potential applications in agricultural biotechnology and plant–microbe interaction studies.