Self-entrapment of Azotobacter vinelandii cultures by gelation of their exopolysaccharides: A way towards next-generation bioinoculants.

Encapsulation of Plant Growth-Promoting Rhizobacteria (PGPR) in hydrogel carriers is a cutting-edge approach in developing agricultural bioinoculants, aiming to improve soil fertility and crop yield. Hydrogels provide protection against environmental stress, though traditional methods using external gel-forming agents limit economic viability. This study presents a novel approach, demonstrating the entrapment of Azotobacter vinelandii, a promising PGPR, within a gel matrix formed by Ca-induced crosslinking of its own exopolysaccharide, alginate. Among the five strains evaluated, A. vinelandii DSM 87, DSM 720, and DSM 13529 showed the highest alginate production, peaking at 4.9 ± 0.6 g/L, 3.5 ± 0.5 g/L, 3.8 ± 0.8 g/L, and enabling stable gel formation by the fourth day of cultivation. These strains also exhibited molecular weights and chemical structures of alginate suitable for effective gelation upon Caaddition. Additionally, these strains demonstrated significant plant growth-promoting activities, including indole acetic acid production (up to 10.5 μg/mL), siderophore release, and phosphate solubilization, further validating their potential for sustainable bioinoculant production. Finally, the viability of the A.vinelandii cells released from the gels was experimentally verified. Our findings support a feasible, cost-effective method for bioinoculant production that leverages A. vinelandii's intrinsic capabilities, offering a sustainable alternative to conventional agricultural practices.

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