Immobilization of a biostimulator microbial consortium on bacterial cellulose and its effect on onion growth, soil nutrient status and the microbial community

The immobilization of plant growth-promoting rhizobacteria (PGPR) in biodegradable polymeric networks is a promising strategy for protecting them from environmental stresses and optimizing their plant-beneficial functions. In this study, a microbial consortium of Pseudomonas stutzeri and Beijerinckia mobilis was immobilized in bacterial cellulose (BC) produced by Komagataeibacter xylinus. Its efficacy was evaluated in onion (Allium cepa) under three treatments: uninoculated control, free cells, and immobilized cells, during a field trial conducted in the 2025 winter cropping season at El-Kharga Oasis, New Valley Governorate, Egypt. Both inoculation forms significantly (P < 0.05) enhanced plant growth, nutrient uptake, and soil fertility, with immobilized cells increasing bulb yield by 44.9% over the control and outperforming free cells. Treatments elevated N, P, K levels in bulbs and soil, with immobilized cells showing superior nutrient mobilization. The microbial diversity in the onion rhizosphere was assessed at harvest. Ecological diversity indices revealed that bacterial treatments, especially in immobilized form, were associated with a short-term reduction in overall microbial diversity, reflecting selective enrichment of plant-beneficial taxa while suppressing non-beneficial competitors. This functional shift enhanced rhizosphere efficiency without long-term detriment to soil health, as confirmed by post-harvest observations. The novelty of this work lies in the field-scale validation of BC as a biodegradable, highly porous carrier that protects PGPR under arid conditions while simultaneously modulating rhizosphere communities. This study highlights microbial immobilization in BC as a robust, eco-friendly approach to enhance crop yield and soil nutrient dynamics, offering a scalable strategy for sustainable agriculture. Photo 1 Graphical illustration showing PGPR immobilization in biocellulose and its effect on onion growth and nutrient uptake through microbiome modulation.