Bacterial degradation of polycyclic aromatic hydrocarbons on agar plates: the role of biosurfactants

Summary

Colonies of a polycyclic aromatic hydrocarbon (PAH) degrading and biosurfactant producing strain of Pseudomonas marginalis PD-14B, pre-incubated on nutrient agar plates, formed zones of clearing when the agar surface was coated with phenanthrene. Application of a drop of the cell-free biosurfactant solution to the agar surface, followed by coating with phenanthrene film also produced a clear zone against the opaque background of the PAH coating. The results indicate that bacterial colonies generate transparent haloes not only as a result of PAH degradation, as is generally concluded from such tests, but also by solubilization of these hydrophobic compounds, mediated by biosurfactants released by the cells into the agar zone surrounding the colony.