Effect of nutritional and environmental conditions on the production and composition of rhamnolipids by P. aeruginosa UG2.

The production of rhamnolipid biosurfactants by P. aeruginosa UG2 was examined under different culture conditions. Rhamnolipid yield was affected by the nature of the carbon sources, the nutrient concentrations, pH, and age of the culture. Hydrophobic substrates like corn oil, lard (rich in unsaturated and saturated fat), and long chain alcohols maximized biosurfactant production (100-165 mg/g substrate). Hydrophilic substrates like glucose, and succinic acid delivered poor yields (12-36 mg/g substrate). Rhamnolipid production was greater when N as (NH4)(2)SO4 and trace metals were added in several periodic doses rather than at the beginning of the process. Increased biosurfactant production was seen in cultures maintained at neutral pH relative to cultures allowed to develop acidic conditions (pH = 6.25). Although the level of rhamnolipid production was affected by culture conditions, the distribution of rhamnolipid subspecies did not vary between cultures. A dirhamnolipid species containing two 10 carbon alpha-hydroxy fatty acids [Rh2C10C10] was the most abundant in the mixtures (60.6 mol%), while the levels of the monorhamnolipid [RhC10C10] (20.7 mol%) and two dirhamnolipids [Rh2C10C12 and its dehydro variant Rh2C10C12-H2] (18.7 mol%) were similar. Biosurfactant mixtures produced with corn oil as sole carbon source solubilized the herbicide trifluralin [2,6-dinitro-N,N-dipropyl-4-(trifluoromethyl)benzamine] to a greater extent. This suggests that the presence of incompletely metabolized hydrophobic by-products acting as co-solvents can increase the solubilization capacity of biosurfactant mixtures.