EMULSIFIER PRODUCTION AND MICROSCOPIC STUDY OF EMULSIONS AND BIOFILMSFORMED BY THE HYDROCARBON-UTILIZING BACTERIA ACINETOBACTER-CALCOACETICUS MM5

A bacterial strain was isolated from a sample of contaminated heating oil and identified as a strain of Acinetobacter calcoaceticus, named M M5. The bacterial isolate was able to grow on petroleum derivatives an d brought about an emulsification of those compounds. A bioemulsifier was extracted from the culture medium of MM5 strain and partially char acterized. This compound was able to emulsify petroleum fuels and both aliphatic and aromatic pure hydrocarbons and was stable over a wide r ange of temperatures. Studies developed by light, scanning electron an d transmission electron microscopy showed that, during the growth on p etroleum derivatives, the microorganisms were orientated on the surfac e of drops enclosed in a skin or membranous polymer produced by the ba cteria. These droplets may represent the hydrocarbon/water emulsion of the liquid culture. The growth of A. calcoaceticus MM5 on media conta ining both hydrocarbon and water-soluble substrates as carbon sources also results in the formation of a film, consisting of amorphous and m embranous layers. The bacteria were connected to the biofilm and showe d intercellular contacts through cell-surface appendages, forming a co mplex network. The importance of the biofilms for bacterial adhesion t o oil droplets and for its nourishment is discussed.