Physicochemical and surface-active properties of biosurfactant produced using molasses by a Pseudomonas aeruginosa mutant

Production of a microbial surfactant was studied by growing Pseudomonas aeruginosa EBN-8 mutant on varying concentrations (on the basis of total sugars) of clarified blackstrap molasses as a sole carbon and energy source with or without auxiliary synthetic nitrogen source in 250 mL shake flasks. The progress of fermentation process was monitored by measuring the production of metabolites, and surface-active and emulsification properties of the cell-free culture broth. The biosurfactant was isolated from the supernatant by acid precipitation followed by solvent extraction. The amount of rhamnolipids produced was determined by the orcinol method. The highest dry cell biomass (1.67 g/L) and rhamnolipid (1.45 g/L) yields were observed, at 96 h of incubation on 2% total sugars-based molasses amended with sodium nitrate (at C:N, 20:1) with the product yield related to dry cell biomass (Y _P/X, g/g) of 0.869, specific product formation rate (V, h⁻¹) of 0.295 and volumetric productivity rate (P _V, g/L/h) of 0.015. The surface tension of this culture medium dropped to 28.0 from 50.0 mN/m.

Keywords:

• Biosurfactant
• Molasses
• Product Yield
• Pseudomonas aeruginosa
• Surface-active
• Surface tension

Acknowledgments

The authors acknowledge the Higher Education Commision, Islamabad for providing the funds for research, and Prof. Dr. Syed Mustafa, Director, NCE in Physical Chemistry, University of Peshawar and Dr. A.M. Khalid, Ex-Director, NIBGE, Faisalabad for permission to coduct this collaborative research. Zulfiqar Ali Raza thanks his beloved parents, Dr. M.I. Rajoka, Deputy Chief Scientist, S.I., NIBGE, Faisalabad and Ms. Asma Rehman, Researcher, NIBGE, Faisalabad for their encourgment and help.

Notes

*Values are given in mg/L or specified, otherwise. The values are averages of three replicate readings.

*Values are averages from three independent cultures.

*Values of E-24, EC, U ₅₄₀ and K _d were measured against n-hexadecane. ‘−’ = no value. The values are averages from 3 independent cultures.