Rhamnolipids are a mixture of the homologs species due to variations in the rhamnose units and β-hydroxy fatty acid moieties, mainly including Rha-C10-C10, Rha-Rha-C10-C10, and Rha-C10. In this study, strain P. aeruginosa YM4 was selected for its capacity to efficiently produce di-rhamnolipid (Rha-Rha-C10-C10) as the predominant component with soybean oil and glycerol as carbon source, accounting for 64.8% and 85.7% of total products, respectively. The critical micelle concentration (CMC) of rhamnolipid products varies with the content of di-rhamnolipid, whereby lower CMC values corresponding to higher di-rhamnolipid contents. The rhamnolipids containing 85.7% di-rhamnolipid had the lowest CMC value of 50 mg/L. Accordingly the viscosity-reducing efficiency and oil-washing efficiency of rhamnolipids increased with higher di-rhamnolipid component. At a concentration of 500 mg/L, the rhamnolipids containing 85.7% di-rhamnolipid worked best and showed 82.5% oil-washing efficiency, which offered great promise for applications in enhanced oil recovery. The results showed the variation of structure and composition of rhamnolipids had a significant effect on their application.
Keywords: Pseudomonas aeruginosa; biosurfactant; di-rhamnolipid; microbial enhanced oil recovery; rhamnolipid.