Optimizing C:N Ratio, C:P Ratio, and pH for Biosurfactant Production by Pseudomonas fluorescens

Abstract

Aim: To optimize the combination of selected culture medium parameters so as to achieve maximum biosurfactant production from Pseudomonas fluorescens. Study Design: (1) Culturing P. fluorescens for biosurfactant production using a glycerol-mineral salt media with variations in  ratio, carbon and phosphorus ratio (C:P ratio), and pH, (2) Screening for biosurfactant activity, (3) use of Response Surface Methodology in determining the combination of the factors that will lead to maximum biosurfactant production. Place and Duration of Study: Department of Microbiology, Faculty of Science, University of Port Harcourt, Nigeria, between September 2016 and June 2017. Methodology: Pseudomonas fluorescens was cultured for biosurfactant production using glycerol-mineral salt media with variations in carbon and nitrogen ratio(C:N ratio), C:P ratio, and pH. Combination of these factors was optimized via the use of Response Surface Methodology. The range of values of the factors investigated was C:N: 20–60, C:P: 10–16, pH: 5.5–8.5. Fifteen experimental runs were carried out. Results: At the end of the experimental runs, the surface tensions of the culture broths ranged from 30.66 – 51.90 mN.m-1. The surface tensions were fitted into the generalized polynomial model for 3-factor design. The model was worked out to be Y = 296.5533 – 34.4456X1 + 0.602833X2 – 23.4019X3 – 0.0545 X1X2 + 1.088889X1X3 + 0.020417 X2X3 + 1.663333X12 – 0.00596X22 + 0.551944X32. Prediction profiles generated from this model showed that the lowest surface tension, indicating maximum biosurfactant production, was achievable at a combination of pH 5.5, C:N = 20, and C:P = 16. Use of this combination for biosurfactant production resulted in reduction of the surface tension of the broth culture from 60.04 mN.m-1 to 30.64 mN.m-1. This almost tallied with the predicted value of 30.57 mN.m-1. Conclusion: The optimized combination avoided wastage of the carbon source. It is thus economical to carry out optimization procedures before proceeding to commercial production of biosurfactants.