Chemically emulsified crude oil as substrate for bacterial oxidation: differences in species response.

Four bacterial species were tested for their abilities to oxidize alkanes in crude oil in water emulsions. The emulsions were prepared by nonionic sorbitan ester and polyoxyethylene ether surfactants. The oxidation rates were measured as initial attack on the emulsions by resting cells pregrown in crude oil media. The bacteria responded differently and both positive and negative effects of surfactant amendment were observed. The same surfactant affected various bacteria differently and the response to the surfactant amendment depended on the physiological state of the bacteria, i.e., exponential versus stationary growth phase. The surfactants caused a marked decrease in cell adhesion to the oil phase for all the bacteria, irrespective of the growth phase and any positive effect on the oil oxidation rates. The response of Deleya salina 128 to polyoxyethylene surfactant emulsified crude oil depended on the length and structure of the hydrophobic tail, the number of hydrophilic ethoxy groups, and the relative proportion of the hydrophobic and hydrophilic constituents in the individual surfactant.