Encapsulation of <i>Acidithiobacillus thiooxidans</i> in Sulfur-Loaded Hydrogel Films for Increased Nutrient Uptake by Plants

Designing smart carrier materials for inoculants used in agriculture is essential to ensuring proper shelf life and cell survival in soil. Herein, we propose to encapsulate Acidithiobacillus thiooxidans and elemental sulfur (ES) particles in a single fertilizer material based on biodegradable hydrogel (HG) films made of carboxymethylcellulose cross-linked by citric acid (CA). The goal was to study the direct availability of ES to the bacterium for improved cell survival and sulfate delivery to plants. Film swelling was evaluated as a method for bacterium inoculation. HG films cross-linked with 5 wt % CA displayed a superior swelling ratio than with 10 wt % CA (129 and 10 g·g–1, respectively) and were less affected by the acid pH used forA. thiooxidans growth. The encapsulated bacterium proved to be viable, achieving up to 62% of ES oxidation after reactivation in culture medium. Soybean plants fertilized with the HG films reached 36% of sulfur use efficiency, comparable to the performance of the soluble positive control, thus confirming its effectiveness as a sulfur biofertilizer.