Effect of pH and salinity on the emulsifying capacity and naphthalene solubility of a biosurfactant produced by Pseudomonas fluorescens

Abstract

A biosurfactant with a low critical micelle concentration, CMC (290 mg L −1), was produced by a Pseudomonas fluorescens strain using olive oil. Measurements of surface tension and emulsification index (E24) showed a positive effect on alkaline pH and a high level of tolerance to ionic strength of the product. Above the CMC, naphthalene solubility was affected by biosurfactant concentration (3–7 times its aqueous solubility), pH and salinity; for 0.5–1.5 g L −1 of biosurfactant, pH 7 and no salinity, naphthalene solubility was about 7-fold its aqueous solubility. The solubility reached a saturation value (205 mg L −1) when biosurfactant concentration exceeded 1.5 g L −1. For alkaline pH or high salinity (above 10%) the solubility decreased by more than 50%. The weight solubilization ratio decreased from 0.63 to 0.015 for increasing biosurfactant concentration up to 1.5 g L −1, alkaline pH or high salinity; and reached a constant value for 4.0 g L −1 biosurfactant irrespective of pH and salinity (in the range of 0.02–0.05 g L −1). In all cases, the solubility of naphthalene in water was enhanced by the biosurfactant addition, showing its potential for application in bioremediation of polycyclic aromatic hydrocarbons contamination in extreme environments.