Encapsulation of Plant Growth-Promoting Bacteria with Gum Arabic Hydrogels: A Potential System for Sustainable Agriculture

One of the significant challenges of the twenty-first century will be feeding the growing world population while reducing the environmental impact and costs of agricultural production. In the case of extensive cropping, using mineral fertilizers or agrochemicals can contaminate the environment, decreasing the rivers and soil health and contributing to the emission of greenhouse gases. In this scenario, plant growth-promoting bacteria (PGPB) or inoculants have emerged as an alternative for overcoming the need for agrochemicals. The PGPB has gained wide prominence as an alternative to enable more sustainable, low-cost, and high-yield agriculture. It can promote plant growth by producing ammonia, from atmospheric nitrogen, and phytohormones through symbiotic relationships. However, the inoculant industries face many challenges related to the biotic and abiotic stress in soil, which decreases the bacteria's survival, and its efficiency after inoculation. To enhance the effectiveness of microbial inoculants herein, we describe the encapsulation of A. brasilense FP2 (wild-type) into gum Arabic-based hydrogels (HG). A high population of encapsulated A. brasilense (107 CFU/g of dry hydrogel) could survive in the polymeric matrix for seven months. The effect on plant growth-promoting was evaluated on maize (Zea mays), which was the plant model. Compared with inoculation via furrow, the encapsulated PGPB enhanced root diameter and volume above 20%. In addition, it resulted in increments above 60% for root and shoot fresh weight compared to the uninoculated HG. Our results indicated that the gum Arabic hydrogels protect A. brasilense and are suitable for biofertilizer formulations.