(721a) Evaluation of Microbial Lipopeptide Biosurfactants for Oil-Spill Remediation

The selection of a surfactant is influenced by its efficacy and environmental impact and may vary depending on the application. There is an increasing demand for biodegradable and non-toxic surfactants in oil spill remediation. Currently, surfactants are mainly derived via chemical synthesis from petroleum-based hydrocarbons. Lipopeptide biosurfactants, produced by microorganisms, are favored for their attractive surface-activity, biocidal and physiological properties.
In the present study, the properties of two lipopeptide biosurfactants and several commercially-available synthetic surfactants were compared. Both biosurfactants, surfactin and FA-Glu, were produced using genetically-modified strains of Bacillus subtilis on glucose-mineral salts media. With both surfactants, rates of synthesis slowed after ~24 h with depletion of the carbon source. Typical titers from shake flasks were ~200-400 mg/L and ~5.5-6.0 g/L, for FA-Glu and surfactin respectively. When they were produced in large fermentors, the surfactants were recovered via foam fractionation and were enriched several fold over surfactant levels in the residual broth. The initial growth rate of FA-Glu producing cells was faster than that of surfactin-producing cells. The surfactants were recovered at purities of >98% and used in physico-chemical and toxicity experiments. Critical micelle concentrations (CMC) of surfactin and FA-Glu were 0.015 and 0.10 g/L, respectively, in distilled water, and were comparable to that of Corexit 9500, a commercially-available synthetic surfactant. Higher CMCs and lower dispersant-to-oil ratio (DOR) values were observed in saline. This was most probably due to the effects of electrolyte and pH on these properties. Both biosurfactants were more effective oil dispersants than Corexit in fresh water. However, in saline, surfactin was most effective, while Corexit was superior to FA-Glu. Fish survival trials showed that surfactin was the most toxic, while FA-Glu had the lowest toxicity of the surfactants tested. Toxicity increased with elevated saline levels; however, with FA-Glu, the effect of saline on toxicity was minimal.