Evaluation of different carbon and nitrogen sources in production of biosurfactant by Pseudomonas fluorescens Original Research Article

The production of a biosurfactant by Pseudomonas fluorescens Migula 1895-DSMZ was studied. Cultures conditions involving variations in carbon and nitrogen sources and different C:N ratios were examined at constant temperature and pH, with the aim of increasing productivity in the process. Biosurfactant synthesis was followed by measuring surface tension and emulsifying index E24. The best results were obtained when using olive oil and ammonium nitrate as carbon and nitrogen sources respectively with a C:N ratio of 10. The production of biosurfactant was growth associated as indicated by the growth and biosurfactant production kinetics. The surface tension was reduced to below 32 dyne/cm and with emulsification index E24 of 65% in 36 to 48 h. The properties of biosurfactant that was separated by acetone precipitation were investigated . The biosurfactant was a rhmnolipid-type in nature as a positive rhamnose assay was tested positive. It had a good foaming and emulsifying and antimicrobial activities. It showed stability during exposure to high temperatures (up to 120°C for 15 min), high salinity (10% Nacl) and a wide range of pH. Analysis by infrared spectroscopy (FTIR) and HPLC were also performed.