Biopolymer-based multilayer capsules for protection and controlled release of Pseudomonas fluorescens T17-4 and Bacillus velezensis VRU1

Plant growth-promoting rhizobacteria (PGPR) are widely recognized as sustainable agricultural inputs because they enhance nutrient availability, reduce reliance on chemical fertilizers, and improve soil and plant health. However, their field performance is often limited by reduced viability and stability under environmental stresses. This study aimed to develop and compare double-layer and multilayer polysaccharide–protein–based encapsulation systems to improve the protection, long-term stability, and controlled release of PGPR. Pseudomonas fluorescens T17-4 and Bacillus velezensis VRU1 were encapsulated using an alginate–whey protein isolate core, with successive outer layers of apricot gum and pectin to form double-layer and multilayer capsules. Mesoporous silica nanoparticles were added to further reinforce the capsule structure. The multilayer encapsulation system outperformed the double-layer formulation, showing higher encapsulation efficiency (> 90%), improved structural integrity, enhanced long-term stability with over 90% bacterial viability after six months, and a more controlled release profile. These findings demonstrate that multilayer polysaccharide–protein encapsulation is an effective strategy for protecting PGPR and ensuring their sustained delivery, highlighting its potential for developing robust biofertilizers in sustainable agriculture.