Physicochemical Determinants of Storage Stability in Spore-Based Bacterial Biopreparations for Agricultural Use

The stability of spore-forming soil bacteria is crucial for their effective use in agricultural biopreparations. This study evaluated the long-term survivability of selected strains (Paenibacillus amylolyticus, Priestia megaterium, Bacillus velezensis, Bacillus subtilis, and Bacillus licheniformis) with potential applications in biopreparations for crop residue decomposition. The effects of different storage and preservation conditions on vegetative cells and bacterial spores were studied over 12 months. Bacteria were stored at different temperatures (15 °C, 21 °C, 30 °C), pH levels (5, 9, and post-cultivation liquid pH), and osmotic pressures (2%, 5%, and 10% of carbamide, calcium chloride, and multicomponent fertilizer). Additionally, freeze-drying, spray-drying and freezing were performed using cryoprotectants (skimmed milk, trehalose, and glycerol). The results showed that bacterial stability depended on both the strain and storage conditions. Vegetative cells of P. amylolyticus and B. velezensis were most sensitive to temperatures of 30 °C, whereas the spores of most strains demonstrated high temperature resistance. The tested strains exhibited better survivability at pH 5 than pH 9. The addition of calcium chloride, carbamide, or multicomponent fertilizer proved beneficial for maintaining viability, especially increasing spore numbers. Trehalose and skimmed milk were the most effective cryoprotectants overall, though efficacy varied by strain and cell form. These findings provide insight into the optimal conditions for preserving the bacterial viability of spore-producing bacteria in bioformulations, which is crucial for maintaining their effectiveness in agricultural applications.