Preparation of New Generation of Bio-inoculants and their viability for applicational potential in agriculture

abstract

English

Azotobacter vinelandii is a plant-growth-promoting rhizobacterium (PGPRs), capable of synthesizing two completely different biopolymers with great application potential. Polyhydroxyalkanoates (PHA) are accumulated intracellularly in a form of intracellular granules, whereas alginate is produced extracellularly as an oxygen barrier for the cell. Moreover, A.vinelandii reveals also other auspicious characteristics such as the capability of N2 fixation or production of phytohormones positively stimulating cell growth, therefore, it can be considered to be an interesting plant growth-promoting bacterium. In agricultural demands, the use of PGPRs as bio-inoculants increasing plant and crop yields can be an ecological alternative to conventional fertilizers. To protect bacterial cells and sustain long-term effect of inoculant application, we developed the novel concept in which bacteria are encapsulated into hydrogel-based carriers by using self-produced alginate. This unconventional approach simplifies the encapsulation of bacterial cells and production of hydrogel carriers, which leads to the reduction of the cost, and expands its usability in numerous applications. In this work, the alginate extracellularly produced by the bacteria was crosslinked with a gelation agent (calcium chloride solution, citric acid, magnesium chloride) to form a hydrogel carrier with encapsulated bacteria. Firstly, we screened several strains of A. vinelandii from public collections of microorganisms and select three of them with a sufficient production capacity concerning alginate and PHA and suitable gelation properties (DSM 87, DSM 720 and CCM 289). The produced alginate reached up to 4.9 ± 0.6 g/l by the strain DSM 87, whereas by the strains DSM 720 and CCM 289 alginate concentration ranges between 1.67 (±0.5) – 2.55 (±0.02) g/l. The content of polyhydroxybutyrate ranged from 30 to 50% of cdw in all the strains. The stability and strength of the bacterial gels depend on the type of bacterial strain and gelation agent, which is proved by rheology measurements, SEM and flow cytometry. According to our results from viability tests, the bacteria entrapped in a gel matrix are viable and cultivatable, which confirms the feasibility and viability of the novel concept.

Plant growth-promoting rhizobacteria, PGPRs, alginate, polyhydroxyalkanoates, bioinoculants

ČERNAYOVÁ, D.; SEDLÁČEK, P.; SLANINOVÁ, E.; TRUDIČOVÁ, M.; GAŠPAROVÁ, D.; OBRUČA, S.

16. 9. 2022

HES-SO Valais-Wallis

Sion, Switzerland