Transport of Pseudomonas aeruginosa in Porous Media Mediated by Low-Concentration Surfactants: The Critical Role of Surfactant to Change Cell Surface Hydrophobicity

Transport of P. aeruginosa ATCC 9027 in quartz sands mediated by low-concentration surfactants of sodium dodecyl benzene sulfonate (SDBS) or Triton X-100 was investigated with column experiments. P. aeruginosa ATCC 9027 was cultured with glucose and hexadecane to produce cells with different initial cell surface hydrophobicity (CSH). Transport behavior of cells was characterized by breakthrough curves (BTCs) and deposition rate coefficients (k_d) values were estimated by fitting the BTCs using colloid transport models. Relations between k_d and CSH represented by bacterial-adsorption-to-hydrocarbon fraction (BATH fraction) and between k_d and cell surface charge represented by zeta potential were analyzed to quantitatively describe the effect of surfactants on cell transport. Results showed that at low concentrations the ionic SDBS increased cell surface charge while the nonionic Triton X-100 had no effect, while both of them caused significant differentiation of CSH. The kinetic attachment-detachment model with blocking was the best among the five models tested to fit BTCs and low-concentration SDBS and Triton X-100 caused remarkable change of k_d. A good linear relation between k_d and cell BATH fraction was observed (R² = 0.82), whereas the linearity between k_d and total zeta potential of cell and sand was poor (R² = 0.11). The data reconstructed from our previous studies showed that the linearity between k_d and cell BATH fraction also presented in sands and glass beads for low-concentration rhamnolipid biosurfactant. In all, these results showed that CSH plays a critical role in cell transport in porous media and changing CSH is a common mechanism for low-concentration surfactants to mediate the transport, which implies the potential of using low-concentration surfactants to regulate bacterial transport for bioaugmentation.