Amidated Pectin Hydrogel as a Carrier for Azospirillum sp. in Agricultural Applications

Abstract Plant growth-promoting bacteria (PGPB) are an important technology for increasing crop productivity, with the genus Azospirillum being widely used in grass cultivation. The encapsulation of PGPB in hydrogels represents a promising technology, providing a safer environment for bacterial adaptation and controlled release into the soil, thereby improving their survival. This study investigated the encapsulation of three strains, A. brasilense AbV5 and HM053, and A. argentinense Az39, in amidated pectin (PAm) hydrogels. Three concentrations of PAm (1–3%) were tested, with 3% forming the most regular-shaped beads, which were subsequently used for encapsulation. After encapsulation and drying, the encapsulated population was 7.8 × 10⁷ CFU/g for AbV5, 6.3 × 10⁷ CFU/g for HM053, and 2.5 × 10⁹ CFU/g for Az39. The Az39 strain was the most resistant to the drying process. Cell viability showed no significant reduction after 45 and 60 days for AbV5 and HM053, respectively, whereas Az39 maintained the initial population for 15 days. The beads were biodegradable, with over 94% mass loss after 15 days in soil burial. The bacterial release test showed no bacteria released within the first 48 h, allowing them to stabilize in the environment before release. After this period, release occurred quickly, and the population remained stable for 15 days. These results demonstrate that encapsulation in PAm hydrogels is a viable carrier strategy that warrants further evaluation under plant-growth and field conditions.