SELF-ENTRAPMENT OF AZOTOBACTER VINELANDII VIA IN SITU ALGINATE GELATION BY A DUAL BIOPOLYMER APPROACH FOR BIOCHAR ENHANCED SEED COATING APPLICATIONS

SELF-ENTRAPMENT OF AZOTOBACTER VINELANDII VIA IN SITU ALGINATE GELATION BY A DUAL BIOPOLYMER APPROACH FOR BIOCHAR ENHANCED SEED COATING APPLICATIONS

Abstrakt

Global agriculture is currently facing major challenges caused by fertilizer shortages, political instability, and climate change. These pressures highlight the need for sustainable solutions that maintain crop yields under reduced fertilizer input while preventing soil degradation. This study presents a novel bioinoculant carrier based on the plant growth-promoting rhizobacterium Azotobacter vinelandii. During growth, A. vinelandii synthesizes two important biopolymers: extracellular alginate, which acts as a natural gel-forming agent enabling bacterial self-entrapment, and intracellular poly(3-hydroxybutyrate) (PHB) granules, which enhance bacterial stress tolerance and survival in soil. We introduce a self-entrapment gelation concept in which alginate-producing bacteria form their own protective hydrogel matrix, simplifying bioinoculant production and improving cost efficiency. To validate this approach, selected bacterial strains were subjected to gelation experiments under alginate-promoting conditions using 2% (w/w) CaCl₂. The carrier was further evaluated for functional modification with biochar and lignohumate, as well as for co-cultivation with the non-alginate-producing PGPR strain Azospirillum brasilense. A key finding was that co-cultivation of bacteria directly with biochar was more effective than post-cultivation mixing, resulting in higher cell density and a stronger hydrogel structure, where in situ-produced alginate acted as a binder within the porous biochar matrix. Biochar addition improved bacterial viability during freeze-drying. The application potential was demonstrated using lettuce (Lactuca sativa L.) seed coating. Initial tests with pure bacterial cultures confirmed PGPR activity and the effect of the polymer carrier on germination and growth. Wet gel coating provided more consistent seed coverage than freeze-dried cultures, while optimization of cross-linking conditions was essential for maintaining high germination rates.

Global agriculture is currently facing major challenges caused by fertilizer shortages, political instability, and climate change. These pressures highlight the need for sustainable solutions that maintain crop yields under reduced fertilizer input while preventing soil degradation. This study presents a novel bioinoculant carrier based on the plant growth-promoting rhizobacterium Azotobacter vinelandii. During growth, A. vinelandii synthesizes two important biopolymers: extracellular alginate, which acts as a natural gel-forming agent enabling bacterial self-entrapment, and intracellular poly(3-hydroxybutyrate) (PHB) granules, which enhance bacterial stress tolerance and survival in soil. We introduce a self-entrapment gelation concept in which alginate-producing bacteria form their own protective hydrogel matrix, simplifying bioinoculant production and improving cost efficiency. To validate this approach, selected bacterial strains were subjected to gelation experiments under alginate-promoting conditions using 2% (w/w) CaCl₂. The carrier was further evaluated for functional modification with biochar and lignohumate, as well as for co-cultivation with the non-alginate-producing PGPR strain Azospirillum brasilense. A key finding was that co-cultivation of bacteria directly with biochar was more effective than post-cultivation mixing, resulting in higher cell density and a stronger hydrogel structure, where in situ-produced alginate acted as a binder within the porous biochar matrix. Biochar addition improved bacterial viability during freeze-drying. The application potential was demonstrated using lettuce (Lactuca sativa L.) seed coating. Initial tests with pure bacterial cultures confirmed PGPR activity and the effect of the polymer carrier on germination and growth. Wet gel coating provided more consistent seed coverage than freeze-dried cultures, while optimization of cross-linking conditions was essential for maintaining high germination rates.

experiments under alginate-promoting conditions using 2% (w/w) CaCl₂. The carrier was further evaluated for functional modification with biochar and lignohumate, as well as for co-cultivation with the non-alginate-producing PGPR strain Azospirillum brasilense. A key finding was that co-cultivation of bacteria directly with biochar was more effective than post-cultivation mixing, resulting in higher cell density and a stronger hydrogel structure, where in situ-produced alginate acted as a binder within the porous biochar matrix. Biochar addition improved bacterial viability during freeze-drying. The application potential was demonstrated using lettuce (Lactuca sativa L.) seed coating. Initial tests with pure bacterial cultures confirmed PGPR activity and the effect of the polymer carrier on germination and growth. Wet gel coating provided more consistent seed coverage than freeze-dried cultures, while optimization of cross-linking conditions was essential for maintaining high germination rates. Keywords: PGPR, Azotobacter vinelandii, alginate, poly(3-hydroxybutyrate), biochar, seed coating, sustainable agriculture

experiments under alginate-promoting conditions using 2% (w/w) CaCl₂. The carrier was further evaluated for functional modification with biochar and lignohumate, as well as for co-cultivation with the non-alginate-producing PGPR strain Azospirillum brasilense. A key finding was that co-cultivation of bacteria directly with biochar was more effective than post-cultivation mixing, resulting in higher cell density and a stronger hydrogel structure, where in situ-produced alginate acted as a binder within the porous biochar matrix. Biochar addition improved bacterial viability during freeze-drying. The application potential was demonstrated using lettuce (Lactuca sativa L.) seed coating. Initial tests with pure bacterial cultures confirmed PGPR activity and the effect of the polymer carrier on germination and growth. Wet gel coating provided more consistent seed coverage than freeze-dried cultures, while optimization of cross-linking conditions was essential for maintaining high germination rates. Keywords: PGPR, Azotobacter vinelandii, alginate, poly(3-hydroxybutyrate), biochar, seed coating, sustainable agriculture

SÚKENÍK, M.; HALEŠ, P.; KALINA, M.; HLAVÁČKOVÁ, B.; ROHÁČ, M.; SEDLÁČEK, P.; OBRUČA, S.

06.09.2027

University College Dublin

Dublin

ISBP 2026 International Symposium of Biopolymers ABSTRACT BOOKLET

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183

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https://www.ucd.ie/sbbs/isbp2026/t4media/ISBP%202026%20Abstract%20booklet%20FINAL.pdf