Emulsifier of Arthrobacter RAG-1: isolation and emulsifying properties

Abstract

The oil-degrading Arthrobacter sp. RAG-1 produced an extracellular nondialyzable emulsifying agent when grown on hexadecane, ethanol or acetate medium. The emulsifier was prepared by 2 procedures: heptane extraction of the cell-free culture medium and precipitation with (NH4)2SO4. A convenient assay was developed for measurement of emulsifier concentrations between 3-75 .mu.g/ml. The rate of emulsion formation was proportional to hydrocarbon and emulsifier concentrations. Above pH 6, activity was dependent upon divalent cations; half-maximum activity was obtained in the presence of 1.5 mM Mg2+. With a ratio of gas oil to emulsifier of 50, stable emulsions were formed with average droplet sizes of less than 1 .mu.m. Emulsifier production was parallel to growth on either hydrocarbon or nonhydrocarbon substrates during the exponential phase but production continued after growth ceased.