A Systematic Comparison of Biosurfactant Effects on Physicochemical Properties and Growth Rates of P. aeruginosa MM1011 and TMU56: A Bioremediation Perspective

Abstract

The main objective of this research was to focus on enhancing the substrate uptake rate of P. aeruginosa using various biosurfactants as well as carbon sources in the medium culture. While hexadecane and Polychlorinated Biphenyls (PCBs) were chosen as hydrophobic carbon sources, the effects of glucose on two strains of P. aeruginosa , MM1011 and TMU56, were evaluated. Two kinds of biosurfactants, including surfactin and rhamnolipid at higher and lower than the critical micelle concentrations were added into the medium. After that, the response of bacterium based on cell surface hydrophobicity (CSH) was measured through the BATH assay. General full factorial technique was used to organize the experiments and analyze the effects of input factors on CSH. Although the both strains showed similar growth trend under conditions of different carbon sources, the order of affinity between the various substrates and the specific growth rates was as PCBs> glucose> nutrient broth> hexadecane. The analysis of variance showed that both type of carbon source and the biosurfactant had a significant effect on the CSH of P. aeruginosa TMU56. However, the P. aeruginosa MM1011 strain had no meaningful reaction in the presence of biosurfactant. High value of coefficient of determination (R 2 =0.95) indicated a good agreement between experimental data and predicted values by models. Moreover, SDS-PAGE analysis demonstrated that the variation in hydrophobicity was a result of fluctuation in the amount of major proteins on the bacteria cell wall. The significant effect of biosurfactant on the P. aeruginosa TMU56 at concentration under critical micelle point was related to the release of more outer membrane proteins (OMPs).