Efficient production of rhamnolipids using glucose as carbon source

Rhamnolipids possess significant application potential across various industries, such as agriculture, petroleum recovery, cosmetics, and pharmaceuticals. Vegetable oils are widely regarded as the preferred carbon source for the microbial synthesis of rhamnolipids. However, the high cost of oil-based feedstocks, combined with the presence of residual oils or fatty acids in the fermentation broth, presents considerable challenges to the downstream separation and purification of rhamnolipids. In this study, glucose was employed as the carbon source for the production of rhamnolipids using the high-yielding strain Pseudomonas aeruginosa YM4. A mixed nitrogen source composed of equimolar concentrations of ammonium nitrogen and nitrate nitrogen constituted the optimal nitrogen source. The pH value was identified as the most critical factor influencing rhamnolipid synthesis by strain YM4. A pH range of 7.0 to 7.4 was found to be favorable for rhamnolipid synthesis, with the optimal pH determined as 7.2. Further systematic optimization of fermentation parameters including the C/N ratio, substrate concentration, and Fe ²⁺ in a 5 L bioreactor resulted in a maximum rhamnolipid titer of 29.7 g/L with 100 g/L glucose and a volumetric productivity of 326.4 mg/L/h. HPLC-ELSD analysis revealed that di-rhamnolipids accounted for 73.8% of the total composition. This study provides a promising prospect for the fermentative production of rhamnolipids using glucose as the substrate.