Descrizione principale (Inglese)

Modern agriculture faces the challenge of balancing crop productivity with environmental sustainability. Eco-friendly alternatives to chemical pesticides are urgently needed. Bacillus subtilis is an effective biocontrol agent, but its application is limited by low stability under field conditions. Poly(3-hy droxybutyrate) (PHB) combined with chitosans can enhance encapsulation, bacterial viability, and controlled release. This study compares two PHB-based approaches: (i) dip-coating with chitosan solutions [1], and (ii) simultaneous electrospinning/electrospraying of COS/B. subtilis [2]. Experimental part: PHB (Mw 330,000 g/mol) was obtained from Biomer (Germany). COS (3,000–5,000 g/mol) was purchased from Kitto Life Co. (Korea). Low- (50,000–190,000 g/mol) and high-molecular-weight chitosan (~600,000 g/mol) were supplied by Sigma-Aldrich (USA). B. subtilis and phytopathogenic fungi were obtained from Biodinamika Ltd. (Bulgaria). PHB fibers (14% w/v) were fabricated and functionalized either by dip-coating with chitosans (COS, low- or high-MW) or simultaneous electrospraying of COS/B. subtilis. Morphological, structural, and surface analyses were performed by SEM, ATR-FTIR, and water contact angle measurements. Mechanical properties were evaluated, and microbiological assays assessed bacterial viability after incorporation and 90-day storage, as well as antifungal activity against Alternaria and Fusarium. Results: PHB/COS mats prepared by electrospinning/electrospraying showed uniform bacterial distribution, enhanced hydrophilicity, and sustained bacterial proliferation. Embedded B. subtilis inhibited Alternaria and Fusarium growth. Chitosan-coated mats improved tensile strength and maintained long-term spore viability, strongly suppressing Alternaria. Discussion: Both methods preserved fibrous PHB while improving mechanical strength and wettability. Chitosan molecular weight influenced viscosity and film formation in dip-coating, whereas COS electrospraying yielded thin, uniform layers. Both approaches ensured bacterial viability and antifungal activity, but electrospinning/electrospraying proved more scalable and efficient. Conclusion: PHB/chitosan-based fibrous biohybrids represent an efficient, sustainable platform for encapsulation and delivery of Bacillus subtilis. Both dip-coating and simultaneous electrospinning/electrospraying approaches ensured long-term bacterial viability and effective antifungal activity, highlighting the potential of natural polymer-based carriers as next-generation eco-friendly formulations for sustainable agriculture. Keywords: electrospinning, encapsulation, biohybrids, Bacillus subtilis, plant protection. Acknowledgements: This research was funded under the Grant BG-RRP-2.011-0005-C01 with financial support from the European Union-NextGenerationEU, Investment C2.I2 “Increasing the innovation capacity of the Bulgarian Academy of Sciences in the field of green and digital technologies”. References: [1]. Krastev V., Stoyanova N., Valcheva I., Draganova D., Naydenov M., Spasova M., Stoilova, O, Polysaccharides 5, 698-714, 2024. [2]. Stoyanova N., Nachev N., Naydenov M., Valcheva I., Spasova M., Stoilova, O. Polymers 17, 1-14, 2025.