Chitosan gel beads represent a promising biopolymer-based delivery system for encapsulating Bacillus subtilis, an effective biocontrol agent in sustainable agriculture. This study investigates the influence of chitosan molecular weight on bead structure, water retention, and swelling behavior, as well as its impact on the viability and antifungal activity of encapsulated B. subtilis. The results demonstrate that chitosan provides a protective microenvironment, enhancing microbial viability, promoting colonization, and ensuring controlled release for prolonged plant protection. Moreover, encapsulation within chitosan gel beads preserved bacterial viability during long-term storage for up to 90 and 180 days. Additionally, the biodegradable and antimicrobial properties of chitosan contribute to pathogen suppression while supporting the plant growth-promoting activities of B. subtilis. The encapsulated bioagent exhibited strong antifungal activity against Fusarium avenaceum and Rhizoctonia solani, highlighting the effectiveness of this eco-friendly approach as an alternative to chemical pesticides. These findings underscore the potential of chitosan-based formulations to enhance the efficacy of bioinoculants, offering a sustainable solution for modern crop management.

Numerous bacterial species can both suppress plant pathogens and promote plant growth. By combining these bacteria with stabilizing substances, we can develop biological products with an extended shelf life, contributing to sustainable agriculture. Bacillus subtilis is one such bacterial species, possessing traits that enhance plant growth and offer effective protection, making it suitable for various applications. In this study, we successfully incorporated B. subtilis into hybrid materials composed of poly(3-hydroxybutyrate) (PHB) fibers coated with chitosan film. The polymer carrier not only supports the normal growth of the bioagent but also preserves its viability during long-term storage. For that reason, the impact of chitosan molecular weight on the dynamic viscosity of the solutions used for film formation, as well as the resulting film’s morphology, mechanical properties, and quantity of incorporated B. subtilis, along with their growth dynamics was investigated. SEM was used to examine the morphology of B. subtilis, electrospun PHB, and PHB mats coated with chitosan/B. subtilis. The results from mechanical tests demonstrate that chitosan film formation enhanced the tensile strength of the tested materials. Microbiological tests confirmed that the bacteria incorporated into the hybrid materials grow normally. The conducted viability tests demonstrate that the bacteria incorporated within the electrospun materials remained viable both after incorporation and following 90 days of storage. Moreover, the prepared biohybrid materials effectively inhibited the growth of the plant pathogenic strain Alternaria. Thus, the study provides more efficient and sustainable agricultural solutions by reducing reliance on synthetic materials and enhancing environmental compatibility through the development of advanced biomaterials capable of delivering active biocontrol agents.

The development of sustainable plant protection strategies requires stable and environmentally compatible delivery systems for beneficial microorganisms. In this study, Bacillus subtilis was encapsulated within chitosan-based cast films to evaluate bacterial viability, sustained biological activity, and antifungal efficacy. Films prepared from chitooligosaccharide (COS) and chitosans of low, medium, and high molecular weight (CS-LMW, CS-MMW, CS-HMW) were characterized in terms of morphology, mechanical performance, and pH-dependent swelling behavior. The viscosity of the chitosan solutions increased markedly with molecular weight from 73 cP (COS) to 614 cP (CS-HMW), while film thickness ranged from 34 ± 1.5 to 57 ± 2.3 µm. Mechanical performance improved significantly with increasing molecular weight, with maximum tensile stress exceeding 200 MPa for CS-HMW films, while swelling studies confirmed pronounced pH-dependent behavior consistent with the polyelectrolyte nature of chitosan. Encapsulation effectively preserved bacterial viability and metabolic activity over time. The intrinsic antifungal activity of chitosan synergized with the biocontrol activity of B. subtilis against Fusarium avenaceum and Alternaria solani. The highest antifungal performance was observed for CS-HMW films, which produced inhibition zones up to 84.6 ± 5.0 mm against A. solani. These findings demonstrate that chitosan-based cast films serve as effective carriers for beneficial microorganisms, providing environmental protection and regulated biological activity. The combination of a bioactive polymer matrix with a potent biocontrol agent represents a promising eco-friendly approach to sustainable plant protection.