Soyabean Oil Concentration Dependent Abundance of Rhamnolipid Homologues Determines Microbial Enhanced Oil Recovery Efficacy In Pseudomonas aeruginosa RA5

In the present research, we isolated rhamnolipid (RLs) biosurfactant producing Pseudomonas aeruginosa RA5 from oil contaminated refinery soil. The proportion of its major mono-RLs and di-RLs homologues; Rha-C10, Rha-C10-C10, Rha-Rha-C10, and Rha-Rha-C10-C10 was investigated with minor change in the Soyabean oil concentration from 2–4%. We report P. aeruginosa RA5 for its capacity to efficiently produce di-rhamnolipid (Rha-Rha-C10-C10) as the predominant component with 2% and 4% soybean oil as a sole carbon source, accounting for 3.7 % and 0.7% of total products, respectively. The critical micelle concentration (CMC) of rhamnolipid products varies with the content of di-rhamnolipid, whereby lower CMC values correspond to higher di-rhamnolipid contents. The rhamnolipids containing 3.7% di rhamnolipid had the lowest CMC value of 206 mg/L. Accordingly, the viscosity-reducing efficiency and oil-washing efficiency of rhamnolipids increased with the higher di-rhamnolipid component. At a concentration of 1000 mg/L, the rhamnolipids containing 3.7% di-rhamnolipid (Rha-Rha-C10-C10) worked best and showed 85% 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.