Many prokaryotic and eukaryotic microorganisms synthesise a wide range of structurally different amphiphilic surface active compounds (SACs). When compared to their synthetic counterparts, many microbial surfactants show superior properties and advantages, such as high surfactant and emulsifying activities, stability in extreme chemico-physical conditions, low toxicity, high biodegradability and the ability of being produced from renewable and cheap raw materials. These characteristics result in a greater acceptability, especially in the applications that cause the dispersion of SACs in the environment. Thanks to their properties, microbial SACs have been evaluated as commercially promising alternatives to chemically synthesised surfactants and emulsifiers in oil industry and bioremediation, as well as in medicine, cosmetic and food industries. The major bottleneck for an industrial application of SACs is production costs. Different strategies have been adopted to make biotechnological processes cost-competitive: (1) use of cheap substrates or wastes (2) optimisation of fermentative conditions and recovery processes and (3) selection of over-producing strains.
Gordonia sp. BS29 was isolated from a chronically dieselcontaminated site. The strain grows using a wide range of aliphatic hydrocarbons and produces extracellular amphiphilic compounds able to stabilise oil/water emulsions. A previous chemical characterisation suggested that the strain BS29 produces lipopolysaccharidic emulsifying agents, both on hydrocarbons and water-soluble substrates. The objectives of this work were to investigate the cultural factors affecting production of the bioemulsifiers by Gordonia sp. BS29 and to find the optimal medium composition for emulsifier production. The kinetics of Gordonia BS29 were investigated in batch cultures on different carbon sources and the kinetic parameters were calculated. The carbon sources which yielded the highest growth rates and yields were selected. Experimental design techniques were used to identify the interactions amongst the type and the concentration of the carbon source, the concentrations of phosphates, ammonium and micronutrients. Statistical optimisation of medium composition was carried out to identify the cultural conditions maximising the emulsifying activity and yields.