Effect of surfactants on pyrene degradation by Pseudomonas fluorescens 29L

The effect of surfactants on pyrene degradation in Pseudomonas fluorescens 29L was investigated. This strain produced 30.1 μM of rhamnolipid equivalents (RE) of biosurfactants on 50 mg of pyrene per liter of medium. The production of biosurfactants was significantly correlated with the water solubility (S _w) of the substrate and the growth rate on it. When chrysene, with a S _w of 2.8 × 10⁻³ mg per liter of water, was the carbon source, 13.1 μM of RE of biosurfactants were produced compared to 10.3 μM of RE of biosurfactants on acenaphthene with a S _w of 1.9 mg per liter of water. No biosurfactants were produced on salicylic acid, catechol, and citrate. All of the strain 29L mutants which grew on pyrene produced biosurfactants while among the mutants which grew on naphthalene, only 88.4% produced biosurfactants. The rhamnolipid mixture, JBR425, inhibited the growth of Strain 29L wild type (WT) and all of its mutants on pyrene. However, these mutants were able to grow in the presence of pyrene when the growth medium was supplemented with 10⁻⁶ mg of emulsan per milliliter of medium. This study implies biosurfactants are produced by Strain 29L as a physiological response to the hydrophobicity of pyrene. The combined use of indigenous biosurfactants and the added biosurfactant, emulsan, is a biotechnology to enhance pyrene degradation by Pseudomonas fluorescens 29L.