Développement de biofertilisants par bioencapsulation des PGPR

Abstract

Microbial encapsulation in alginate matrices represents an innovative solution for improving the efficacy of in sustainable agriculture. In this study, the ionic gelation technique was used to encapsulate two plant growth-promoting bacteria, Bacillus thuringiensis (B25) and Pantoea agglomerans (Pa), in 1% alginate capsules enriched with 5mM proline as an osmoprotectant. Results showed effective encapsulation, with over 99% of bacteria trapped. After 24 months' storage at 4°C, B25 maintained high viability, while the initial Pa concentration of 8,72 × 109 ( 0,04 × 109) CFU/ml was reduced by 99,9% [5,3×104 ( 0,02×104 CFU/g)]. Survival of individually encapsulated bacteria was significantly higher than that of co-inoculated bacteria. Furthermore, the encapsulated bacteria demonstrated a notable ability to colonize Arabidopsis thaliana roots as well as the rhizosphere, rhizoplan and endosphere of durum wheat (Triticum durum), significantly improving plant growth, with significant increases in protein, sugar and chlorophyll contents in wheat. To enhance the viability and efficacy of the microbial formulations, these were optimized by enriching the alginate capsules with natural additives such as clay and talc. Physico-chemical analyses(XRD, FTIR) revealed molecular and structural interactions favorable to matrix stability. Near-perfect encapsulation (> 99.9%) was achieved for all formulations, with exceptional survival rates after 12 months' storage for B25 in alginate matrices enriched with clay and talc. These matrices also demonstrated effective modulation of bacterial diffusion and enhanced protection against UV radiation. Application of the formulations to durum wheatresulted in a significant improvement in growth parameters, reduced oxidative stress (MDA) and higher bacterial density in the rhizosphere for encapsulated versus free bacteria, with successful colonization of internal tissues by Pa. In conclusion, this study demonstrates that encapsulation of B. thuringiensis and P. agglomerans in alginate matrices enriched with natural additives guarantees prolonged bacterial viability, maintenance of PGP activities, controlled release into the rhizosphere, and effective against the damaging effects of UV radiation. These innovative formulations offer considerable potential for the development of sustainable, high-performance bioinoculants, meeting the challenges of modern agriculture while reducing the use of chemical inputs.