Effects of nutrition optimization strategy on rhamnolipid production in a Pseudomonas aeruginosa strain DN1 for bioremediation of crude oil

An indigenous rhamnolipid biosurfactant-producing Pseudomonas aeruginosa strain DN1 was isolated from petroleum-contaminated soil samples which could use crude oil as the sole carbon and energy source. A high yield of 25.9 g/L rhamnolipid mixture was achieved in a shake flask by nutrition optimization strategy based on high throughput screening of strain DN1, supplemented with palm oil and 5.0 g/L sodium nitrate at a C/N ratio of 20. These rhamnolipids reduced the surface tension of water from 45.23 to 25.88 mN/m with a critical micelle concentration of 50 mg/L, and were able to emulsify several hydrocarbons and showed excellent emulsification (100%). A total number of 6 monorhamnolipid homologues (Rha-C8-C8; Rha-C10:1-C8; Rha-C12:2; Rha-C12; Rha-C14-C16; Rha-C16-C16) and 7 dirhamnolipid homologues (Rha-Rha-C10; Rha-Rha-C12; Rha-Rha-C14; Rha-Rha-C8-C10; Rha-Rha-C10-C8:1; Rha-Rha-C10-C10; Rha-Rha-C10-C12) were detected by liquid chromatography/ mass spectrometry analysis allied to electrospray ionization mass spectrometry. In addition, strain DN1 exhibited an enhanced capacity to degrade crude oil (90.52%) by its rhamnolipids. The results indicated that the use of nutrition optimization strategy will be the most popular process strategy for high rhamnolipids productivity by this strain for in situ bioremediation of crude oil.