Optimization of rhamnolipid biosurfactant production by mangrove sediment bacterium Pseudomonas aeruginosa KVD-HR42 using response surface methodology

Rhamnolipid biosurfactant production by a novel Pseudomonas aeruginosa strain KVD-HR42 was optimized with statistical approaches. The produced biosurfactant showed surface active properties with stable emulsification activities. Based on the results of Plackett–Burman design, first-order polynomial model was developed and the following significant variables were determined viz., Karanja oil, sodium nitrate and pH. Response surface methodology experimental design was performed by Box–Behnken design to study the concentration of each component. The response plots resulted in the following optimized conditions; Karanja oil (23.85 g/L) sodium nitrate (9.17 g/L) and pH (7.8) which yielded an average biosurfactant production of 5.90±2.1 g/L at 48 h, and 37 °C temperature. The statistical approach resulted in enhanced biosurfactant production. The biosurfactant showed excellent emulsion forming capabilities and could reduce the surface tension to 30.14 mN/m at a CMC value of 100 mg/L. The biosurfactant was found to be stable at extreme conditions of temperature, pH and NaCl concentrations. Additionally surface active nature of the crude biosurfactant was demonstrated using oil displacement assay with a clearance zone of 19.26±0.23 cm2. Our results signify that the biosurfactant has a great industrial potential as a cleansing agent at adverse environmental conditions and provide better alternative to synthetic surfactants.