Optimizing Carbon/Nitrogen Ratio for Biosurfactant Production by a Bacillus subtilis Strain

A Bacillus subtilis strain isolated from contaminated soil from a refinery has been screened for biosurfactant production in crystal sugar (sucrose) with different nitrogen sources (NaNO3, (NH4)2SO4, urea, and residual brewery yeast). The highest reduction in surface tension was achieved with a 48-h fermentation of crystal sugar and ammonium nitrate. Optimization of carbon/nitrogen ratio (3, 9, and 15) and agitation rate (50, 150, and 250 rpm) for biosurfactant production was carried out using complete factorial design and response surface analysis. The condition of C/N 3 and 250 rpm allowed the maximum increase in surface activity of biosurfactant. A suitable model has been developed, having presented great accordance experimental data. Preliminary characterization of the bioproduct suggested it to be a lipopeptide with some isomers differing from those of a commercial surfactin.