Petroleum-derived hydrocarbons are among the most persistent soil contaminants, and some hydrocarbondegrading
microorganisms can produce biosurfactants to increase bioavailability and degradation. The aim
of this work was to identify biosurfactant-producing bacterial strains isolated from hydrocarboncontaminated
sites, and to evaluate their biosurfactant properties. The drop-collapse method and minimal
agar added with a layer of combustoleo were used for screening, and positive strains were grown in liquid
medium, and surface tension and emulsification index were determined in cell-free supernantant and cell
suspension. A total of 324 bacterial strains were tested, and 17 were positive for the drop-collapse and
hydrocarbon-layer agar methods. Most of the strains were Pseudomonas, except for three strains
(Acinetobacter, Bacillus, Rhodococcus). Surface tension was similar in cell-free and cell suspension
measurements, with values in the range of 58 to 26 (mN/m), and all formed stable emulsions with motor
oil (76-93% E24). Considering the variety of molecular structures among microbial biosurfactants, they
have different chemical properties that can be exploited commercially, for applications as diverse as
bioremediation or degradable detergents.
