Production of rhamnolipids with a high specificity by Pseudomonas aeruginosa M408 isolated from petroleum-contaminated soil using olive oil as sole carbon source

Rhamnolipids (RLs) represent a very promising class of biosurfactants that have many applications as biocompatible and biodegradable emulsifiers. We have isolated a Pseudomonas aeruginosa strain, denoted strain M408, from petroleum-contaminated soil of the Liaohe oil field (northern China) that is able to produce RLs with a high specificity when grown on olive oil as the sole carbon source. Product analysis of these RLs showed that only di-RLs (F1 sample), including rhamnose (Rha)-Rha-C10-C10 and Rha-Rha-C10-C12/Rha-Rha-C12-C10, and a single mono-RL (F2 sample) of Rha-C10-C10 were produced by the isolate. Further testing revealed that these F1 and F2 products were able to reduce the surface tension of water to 31 and 27 mN/m, respectively. The critical micelle concentration was 120 and 60 mg/L for the F1 and F2 products, respectively. The F1 and F2 products also showed good emulsion stability, achieving an emulsion capacity of 87 and 90 %, respectively, with atoleine after 24 h at a low concentration of 100 mg/L. Maximum production of the RLs was obtained after optimization of the culture conditions, with a 6.85-fold increase in the yield of the RLs, up to 12.6 g/L, relative to the yield before optimization.