Microencapsulation of Bacillus megaterium in cationic starch/PVA-based matrices

The increasing demand for sustainable and effective agricultural bio-based products is driving innovation in encapsulation technologies for beneficial microorganisms, such as Bacillus strains, known for promoting plant growth and controlling pathogens. This study proposes an efficient methodology for encapsulating Bacillus megaterium within microparticles using a simple cross-linking/emulsion process based on Cationic Starch (CS) and Polyvinyl Alcohol (PVA). Citric acid (CA) and Sodium Trimetaphosphate (STMP) were employed as cross-linking agents, while bentonite (Bent) was added to modify the materials. The resulting microparticles exhibited a range of properties influenced by the cross-linking agents and bentonite. Encapsulation matrices with STMP and STMP-Bent demonstrated superior performance in providing controlled bacterial release and enhanced protection under adverse conditions. These matrices maintained up to 95 % of the initial cell viability after exposure to heat (55 °C for 24 h), and up to 98 % viability after exposure to UV light (180 min) or pesticides (30 °C for 24 h). In contrast, matrices containing CA or CA-Bent, as well as free bacteria, showed significantly lower bacterial survival rates in the same tests. In a high-salinity soil test (200 mM), STMP-based matrices provided the best protection for encapsulated bacteria, leading to a 10 % increase in B. megaterium growth. Furthermore, these matrices demonstrated an estimated shelf-life of over 40 months when stored at temperatures of 15 °C, 30 °C, and 45 °C. These findings suggest that CS/PVA matrices cross-linked with STMP offer a promising approach for developing more resilient and effective bio-based agricultural products.