Volatile Organic Compounds of Endophytic Bacillus Strains from Pinus sylvestris L. Seeds: A Comparative HS-GC-MS Study Across Three Nutrient Media

Introduction/Objective Endophytic bacteria of coniferous seeds are promising for developing biological products that enhance tree growth and resistance without chemical agents. Scots pine productivity is declining under climate change and pathogens, yet the Volatile Organic Compound (VOC) profiles of its seed endophytes remain poorly characterised. The objective was to compare the VOC profiles of endophytic Bacillus pumilus E11 and B. amyloliquefaciens E12 from Pinus sylvestris L. seeds in three media differing in carbon source. Methods VOCs in cell-free culture fluids were analysed by Headspace Gas Chromatography with Mass-Spectrometric Detection (HS-GC-MS) on a DB-624 column. Strains were grown in Potato Dextrose Broth and two synthetic media with glucose or sucrose (5 g/L) as the sole carbon source. Each strain-medium combination and its uninoculated blank were analysed in triplicate (n = 3); compounds were identified by NIST matching with retention indices and quantified semi-quantitatively (ppm). Results Eighteen VOCs were detected. In synthetic media, the main metabolite of B. amyloliquefaciens E12 was acetoin (81.5 ppm on glucose vs . 130.8 ppm on sucrose; +60%, p < 0.05). Branched short-chain fatty acids occurred only in E12 on glucose, while tetrahydrofuran (0.9-8.8 ppm) was a strain-specific marker of B. pumilus E11. Discussion The carbon-source-dependent shift in the VOC profile reflects metabolic variability of the isolates. As the study was semi-quantitative and no antifungal or in planta assays were performed, functional roles attributed to individual compounds rest on literature and require experimental validation. Conclusion The two endophytic Bacillus strains show distinct, medium-dependent VOC profiles. B. amyloliquefaciens E12 is a candidate for further study as a producer of growth-associated and potentially protective volatiles, pending biological validation.