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

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. (C) 2010 Elsevier B.V. All rights reserved.