Biodegradable PVA-based films for delivery of Bacillus megaterium as seed coating

The synthetic polymer Polyvinyl alcohol (PVA) is known for its water solubility, non-toxicity, biodegradability, and high biocompatibility with cells. These characteristics make it a promising vehicle for beneficial microorganisms in sustainable agricultural practices. Here, we developed biodegradable films made of PVA crosslinked with citric acid (in concentrations ranging from 0 % to 30 %) to deliver Bacillus megaterium as seed coating. Physical-chemical and morphological analyses showed promising compatibility between PVA and citric acid, with the latter improving the thermal behavior of the films. The addition of 30 % citric acid significantly reduced the swelling and solubility of the films, thereby increasing their resistance to degradation, a crucial quality for seed coating. The film matrix allowed the controlled release of B. megaterium, keeping the cell viability during six months of storage and under external stresses. After exposure to heat and insecticide, the PVA film with citric acid kept cell viability in the same order as the initial concentration, which was not observed in free bacteria that decreased 2-4 orders of magnitude in cell viability. The film with encapsulated B. megaterium also promoted soybean seed germination rates comparable to treatment with commercial polymer and superior to untreated seeds, demonstrating its viability for agricultural applications. The PVA film crosslinked with citric acid showed promising potential for encapsulating Bacillus megaterium and seed coating, benefiting microorganism protection and seed germination performance.