Effects of surfactants on cell surface tension parameters and hydrophobicity of Pseudomonas putida 852 and Rhodococcus erythropolis 3586.

The interaction between bacteria and surfaces is central to many environmental, industrial and medical applications. Surfactants are commonly used in these applications and can potentially influence the bacterium/surface interaction. The effect of surfactants upon bacterial cell surface thermodynamic properties was examined using a combination of contact angle measurements and LW-AB surface free energy calculation. Two bacterial strains, hydrophilic Pseudomonas putida 852 and hydrophobic Rhodococcus erythropolis 3586, and two surfactant types, the anionic biosurfactant rhamnolipid and the non-ionic chemical surfactant tergitol, were examined. The study demonstrated that surfactant treatment could modify cell surface tension parameters including Lifshitz-van der Waals (γ(LW)), electron-donor (γ(-)) and electron-acceptor (γ(+)) and thereby the bacterial cell hydrophobicity, depending on the surfactant type and concentration and the bacterial surface characteristics. Rhamnolipid and tergitol were found to increase P. putida 852 hydrophobicity, but decrease the hydrophobicity of R. erythropolis 3586. The extent of change was dependent on surfactant concentration. Among the three surface tension parameters, γ(-) was found to be the most important in predicting bacterial cell hydrophobicity.