Abstract:
Biosurfactants are amphiphilic tensioactive natural products that are capable of lowering the surface and
interfacial tensions of the growth medium. Efficient biosurfactants are characterized by their ability to enhance
the aqueous solubility of hydrophobic compounds and to emulsify hydrocarbons in aqueous medium.
Improvement in the fermentation technology, strain selection and use of cheaper and renewable substrates
have a vital role in enhancing the production processes of biosurfactant industries. However, large scale
production of biosurfactants has not reached a satisfactory economical level due to their low yields. Several
studies have reported significant effect of carbon sources on the productivity of biosurfactants by different
strains. In the current study medium composition optimization approach was investigated for optimal
biosurfactant production using a combination of hydrophobic and hydrophilic carbon sources by Bacillus
subtillis CN2 strain, previously isolated from hydrocarbon contaminated soil. The study demonstrated that
both quantity and type of carbon sources prompted a significant difference in the amount and activity of the
biosurfactant produced. The hydrophobic carbon sources were found to be superior to hydrophilic ones in
promoting biosurfactants production and surface activity superiority. The strain produced 10-fold more
biosurfactant when growing on oil than when grown on glycerol and significantly higher surface activity as
determined from the emulsification index. In addition to using the hydrophobic substrate sunflower oil as a sole
substrate, addition of sunflower oil (5%, wt/v) in to the growth medium after depletion of hydrophilic substrate
(glycerol) stimulated the production of biosurfactant by more than 200%. Both the type and concentration of
the carbon source were shown to be essential determinants of biosurfactant yield and physicochemical
properties. The result of our study showed that the presence of optimal hydrophobic substrates in the growth
medium triggered release of more biosurfactant through their inductive effect, which shows a promising
potential of the approach for large scale viable biosurfactant production.
