Optimization of mineral nutrients to improve rhamnolipid production by Pseudomonas aeruginosa 6 K-11

BACKGROUND: Rhamnolipids are biosurfactants that have their main application in bioremediation processes. They are able to increase the biodegradation and detoxification rates from industrial effluents. The north of Peru and Iquitos have been not only major oil producers but also have been responsible for oil spills. This study therefore focused on the optimization of mineral nutrients such as nitrogen, phosphorous, calcium and iron to improve rhamnolipids production by Pseudomonas aeruginosa 6 K-11, which was isolated from oil soil in Peru. RESULTS: Pseudomonas aeruginosa 6 K-11 was reactivated in Trypticase Soy Broth by scaling from 5 to 200 mL of culture medium for 8 h at each stage. The culture was centrifuged and placed in 100 mL Siegmund–Wagner medium for 36 h in a 500 mL Erlenmeyer flask. First, it was determined that sodium nitrate, monopotassium phosphate, calcium chloride and iron sulfate were the best sources of mineral nutrients. Then, by using corn oil as carbon source, the ratios obtained for carbon-to-nitrogen and carbon-to-phosphorous were 21.172 and 16.279, respectively. In addition, it was found that the optimal concentration for calcium was 0.046 g L⁻¹ and for iron was 0.003 g L⁻¹. The most influential variables were carbon-to-nitrogen and carbon-to-phosphorus ratio. Finally, 35.124 g L−1 rhamnolipids was produced after 168 h of fermentation with the optimal parameters. CONCLUSION: The optimization of mineral nutrients was an important achieved goal for rhamnolipid production. In addition, this optimization can be used for modifying the culture medium to grow the biosurfactant producer strain.