Metabolite-mediated antagonism of endophytic bacteria against Curvularia lunata in banana revealed by multi-analytical profiling

Curvularia lunata (MLP-01; GenBank accession ON246070) is an important phytopathogen that causes leaf spot disease in Musa paradisiaca , resulting in significant yield losses. In this study, two potent plant growth-promoting endophytic bacteria, Enterobacter cloacae (MRH-06; GenBank accession ON955844) and Achromobacter xylosoxidans (MRH-11; GenBank accession ON955872), isolated from healthy Musa sp. root tissues, were evaluated for their antifungal activity against C. lunata . Dual culture assays showed strong antagonism, with E. cloacae inhibiting 75% and A. xylosoxidans inhibiting 83% of mycelial growth. Extracellular metabolites were extracted with chloroform and ethyl acetate and analysed by gas chromatography–mass spectrometry (GC–MS) and Fourier transform infrared (FT-IR) spectroscopy. GC–MS profiling revealed a diverse range of bioactive metabolites, including phenolic compounds, fatty acids, long-chain hydrocarbons, esters, and nitrogen-containing heterocycles. FT-IR analysis confirmed the presence of hydroxyl, aliphatic, alkene, ester, ether, and amine functional groups, strongly supporting GC–MS-based compound identification. Nuclear Magnetic Resonance (NMR) was also used to identify the compounds. Along with transmission electron microscopy, confocal and fluorescence microscopic images were also taken to locate endophytic bacteria within the root tissue of Musa paradisiaca . Biolog GEN III phenotypic profile of strains MRH-06 and MRH-11 showed a high degree of similarity to Enterobacter cloacae and Achromobacterxylosoxidans ,respectively. HPLC quantification of trypthphan showed higher production of trypthophan by both the bacterial isolate which helps in Indole-3-Acetic Acid (IAA) production and growth promotion. The integrated analytical approach highlights the superior biocontrol potential of A. xylosoxidans compared with E. cloacae and demonstrates the role of endophytic bacterial metabolites as eco-friendly alternatives for the management of C. lunata in banana.