Climate change has intensified desertification and droughts, directly impacting agriculture and livestock. To promote sustainability in Colombian grasslands, AGROSAVIA developed a bioinoculant comprising a synthetic bacterial consortium of three rhizobacteria (Herbaspirillum sp. AP21, Azospirillum brasilense D7, and Rhizobium leguminosarum T88) with plant growth-promoting properties and drought resilience. This study evaluated the co-culture fermentation of these strains in M10 medium, testing different carbon source (SC) concentrations relative to the baseline (T0): T0, T1 (-30%), T2 (-10%), T3 (+10%), and T4 (30%). Fermentations were conducted at 150 rpm and 30°C. Co-culture was initiated with strain T88, followed 24 h later by the addition of strains D7 and AP21. To monitor growth dynamics, the cell viability (CFU/mL) of each strain and the mixed culture was quantified after 24 h and 48 h on LMA agar (30 °C, 72 h incubation). Once the optimal carbon concentration was identified, the co-culture was scaled up in an 8 L stirred-tank bioreactor (STR). The bioreactor results showed enhanced growth, with cell counts exceeding 10⁹ CFU/mL, confirming the feasibility of co-culture fermentation for the development of a sustainable bioinoculant to mitigate drought impacts.