Trifolium alexandrinum L. (berseem) is a major forage legume known for its high nutritional value and importance in animal feeding systems. Enhancing its nutritive profile through sustainable practices can contribute significantly to improving livestock productivity. Plant growth-promoting rhizobacteria (PGPR) have gained attention as eco-friendly biofertilizers that can enhance plant growth and nutrient content. This study aimed to assess the effect of a single PGPR strain (BT1) on the nutritional quality of T. alexandrinum grown under natural field conditions. An open-field experiment was conducted in which seeds were primed with the BT1 strain and irrigated accordingly. An untreated control group was maintained for comparison. The experimental setup included five replicates per treatment. At the vegetative stage, samples were collected and analyzed for nutritional parameters, including dry matter, crude protein, crude fiber, organic matter, PDIE, PDIN, and energy values (UFL and UFV), using standard analytical procedures (AOAC, 1990) and INRA equations. The results indicated that inoculation with BT1 significantly enhanced the nutritional value of T. alexandrinum. Crude protein content increased to 21.53% DM in the BT1-treated group, compared to 16.05% in the control. Organic matter was also higher in the BT1 group (89.70% DM) versus the control (87.48% DM). Although dry matter content was slightly reduced in the BT1 treatment (22.76%) relative to the control (24.35%). Moreover, crude fiber content was slightly lower in the BT1 group (15.74%) than in the control (16.32%). Notably, all modifications observed in the BT1 treatment were in favor of improved forage quality, as reflected by the higher values of energy parameters (UFL and UFV) and protein digestibility indices (PDIN and PDIE) compared to the control. This consistent improvement across multiple nutritional parameters highlights the efficacy of BT1 as a biofertilizer.