Rhamnolipid production by indigenous Pseudomonas aeruginosa J4 originating from petrochemical wastewater

Pseudomonas aeruginosa J4, isolated from wastewater of a petrochemical factory located in southern Taiwan, was used to produce rhamnolipid from a variety of carbon substrates, including hydrophilic substrates, vegetable oils, and mineral oils. The P. aeruginosa J4 strain was able to assimilate the seven carbon substrates examined (namely, glucose, glycerol, olive oil, sunflower oil, grape seed oil, diesel, and kerosene), whereas it grew less efficiently in mineral oils (esp., kerosene). Rhamnolipid production from the J4 strain was affected by temperature and agitation rate, as 30°C and 200 rpm agitation were favorable for rhamnolipid production. The rhamnolipid concentration (C _RL) and production rate (v_RL) was also influenced by the carbon sources used to grow the J4 strain. Similar v_RL (10-12 mg/h/L) and C_RL (1400-2100 mg/L) were obtained from using glycerol, glucose, grape seed oil, and sunflower oil as the sole carbon substrate, while using olive oil delivered the best rhamnolipid production. Maximum C_RL (3600 mg/L) and v_RL (26 mg/h/L) were attained at 10% olive oil. P. aeruginosa J4 also utilized diesel and kerosene for rhamnolipid production but with much lower C_RL and v_RL values Rhamnolipid was purified (nearly 90% pure) from the culture broth. Mass spectrometry and NMR analysis indicate that the purified product contained two types of commonly found rhamnolipids: l-rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoate (RL1) and l-rhamnosyl l-rhamnosyl-β-hydroxydecanoyl-β-hydroxydecanoate (RL2). The rhamnolipid product can reduce the surface tension of water to 31 mN/m with a critical micelle concentration of nearly 50 mg/L. The biosurfactant also achieved a maximum emulsion index of 70 and 78%, for diesel and kerosene, respectively, at a low concentration of about 300 mg/L.