Cryo-EM as a tool for observing alginate-based hydrogels

abstract

English

Hydrogel is an organic-based material, which finds its use in various fields ranging from well-known employment in medicine (wound treatment, scaffolds,...) to rising involvement in agriculture (superabsorbents, controlled release of fertilisers,...). While hydrogels containing chemical fertilisers provide valuable nutrients directly, the unused nutrients remain in the soil, where they accumulate, which negatively influences biodiversity, soil fertility, etc. An alternative approach relies on the use of biological fertilisers (bioinuculants) in the form of plant growth-promoting bacteria (PGPRs). One of the PGPRs is Azotobacter vineladii, a microorganism interesting not only for its plant growth-promoting properties but also for its production of various polymers. Namely polyhydroxyalkanoates (PHAs), biopolymers praised for their properties similar to petrochemical plastics, or alginate, polysaccharide capable of forming a hydrogel. A. vinelandii releases alginate to form a capsule around the cells, which protects them from drying out and from other hostile environmental conditions. The production of alginate is a significant advantage of using A. vinelandii as bioinoculant since there is no need to add the hydrogel-forming polymers to the bacteria for encapsulation, the polymer already in the media is crosslinked and the resulting hydrogel is then processed into the final form of bioinoculant suitable for employment in agriculture. This work aimed to study the morphology of hydrogel formed using different crosslinking agents (namely CaCl2 and glucono-D-lactone), a step necessary to determine the most suitable crosslinker. Since alginate hydrogels are composed of polysaccharides and a substantial amount of water, chemical processing for EM could severely alter the hydrogel ultrastructure. Therefore, cryogenic fixation followed by freeze-fracture and cryo-SEM was proposed to be the most promising technique to study the polymeric net the most closely to the native state.

Hydrogel, alginate, bacteria, freeze-fracture, cryo-SEM.

MRÁZOVÁ, K.; HAVLÍČKOVÁ, A.; ČERNAYOVÁ, D.; HRUBANOVÁ, K.; SEDLÁČEK, P.; KRZYŽÁNEK, V.

30. 8. 2024

EMC

Copenhagen

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