BOOK OF ABSTRACTS 141 IHSS&IWA26 / BRNO / CZECHIA / 23–28 August 2026 Thursday, 27 August 2026 / Hall C Soil Organic Matter, Caustobiolites, and Biochar SL68 Microbial Architects: Plant Growth-Promoting Bacteria Building Their Own Hydrogel Delivery Systems Petr Sedláček1, Martin Súkeník1, Michal Kalina1, Barbora Hlaváčková1, Petr Haleš1, Stanislav Obruča1 1 Faculty of Chemistry, Brno University of Technology, Purkynova 464/118, 61200 Brno, Czech Republic, sedlacek-p@fch.vut.cz The development of sustainable agricultural systems requires innovative strategies that enhance soil functionality while reducing dependence on synthetic fertilizers. Plant growth-promoting rhizobacteria (PGPR) are increasingly recognized as valuable components of biologically based crop management due to their ability to support nutrient cycling, stimulate plant growth, and improve rhizosphere functioning. However, the large-scale deployment of microbial inoculants remains constrained by the cost and complexity of conventional encapsulation technologies. This study presents a novel biofertilizer concept based on the ability of Azotobacter vinelandii to produce extracellular alginate, enabling the formation of self-generated hydrogel matrices of the culture by simple Cainduced crosslinking. The resulting exopolysaccharide-based hydrogels provide both microbial protection and delivery functionality without the need for externally added gelation agents. Beyond technological simplification, this approach offers a unique model system for studying microbial production of biopolymeric matrices that contributes to the stabilization and organization of organic matter in the rhizosphere. A systematic investigation was conducted to identify key factors affecting bacterial growth, alginate production, gel formation, and bioinoculant stability. Among the tested strains, A. vinelandii CCM 289 demonstrated superior exopolysaccharide production, favorable gelation characteristics, and the ability to synthesize plant-beneficial metabolites, including indole-3-acetic acid and siderophores. The study further explored relationships between hydrogel structure, microbial viability, and biological activity, providing insights into how microbial polysaccharide matrices influence the persistence and functionality of beneficial bacteria in soil environments. Particular attention was devoted to combining the self-encapsulation concept with soil amendments rich in organic carbon. Incorporation of biochar or lignohumate resulted in synergistic effects, improving bacterial survival during bioinoculant production while simultaneously introducing complementary soil-conditioning and
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