Effect of low-concentration rhamnolipid on transport of Pseudomonas aeruginosa ATCC 9027 in an ideal porous medium with hydrophilic or hydrophobic surfaces

Abstract

The success of effective bioaugmentation processes for remediation of soil and groundwater contamination requires effective transport of the injected microorganisms in the subsurface environment. In this study, the effect of low concentrations of monorhamnolipid biosurfactant solutions on transport of Pseudomonas aeruginosa in an ideal porous medium (glass beads) with hydrophilic or hydrophobic surfaces was investigated by conducting miscible-displacement experiments. Transport behavior was examined for both glucose-grown and hexadecane-grown cells, with low or high surface hydrophobicity, respectively. A clean-bed colloid deposition model was used for determination of deposition rate coefficients. Results show that cells with high surface hydrophobicity exhibit greater retention than cells with low surface hydrophobicity. Rhamnolipid affects cell transport primarily by changing cell surface hydrophobicity, with an additional minor effect by increasing solution ionic strength. There is a good linear relation between k rhamnolipid-regulated cell surface hydrophobicity presented as bacterial-adhesion-to-hydrocarbon (BATH) rate of cells (R2 = 0.71). The results of this study show the importance of hydrophobic interaction for transport of bacterial cells in silica-based porous media, and the potential of using low-concentration rhamnolipid solutions for facilitating bacterial transport in bioaugmentation efforts.

Effect of low‐concentration rhamnolipid biosurfactant on Pseudomonas aeruginosa transport in natural porous media

“…The retention of the glucose‐grown cells is only slightly weaker than hexadecane‐grown cells (i.e., hydrophobic cells). This is in contrast to transport of the cells in the ideal porous medium of glass beads, in which retention of hydrophobic cells is strong (∼80%) but retention of hydrophilic cells is significantly weaker (∼20%) [ Zhong et al ., ].…”

“…Successful bioaugmentation depends on effective transport of injected microorganisms over considerable distances and adequate distribution of the injected microorganisms throughout the contaminated zone. This has been a focus of numerous studies on bioaugmentation [ Bai et al ., ; Chen et al ., ; Li and Logan , ; Liu et al ., ; Zhong et al ., ].…”

“…A few prior studies, however, showed that rhamnolipids are able to change cell surface properties at very low concentrations (∼10 mg/L) [ Zhang and Miller , ; Zhong et al ., ]. In our prior recent studies, monorhamnolipid at the concentration of 20 mg/L was observed to significantly attenuate hydrophobic interactions between P. aeruginosa cells and glass beads, and thus reduced cell adsorption and enhanced cell transport [ Zhong et al ., ].…”

Advances in applications of rhamnolipids biosurfactant in environmental remediation: A review

“…The successful bioremediation (bioaugmentation in particular) depends on effective transport of injected bacteria over considerable distances and adequate distribution of the injected bacteria throughout the contaminated area (Liu, Zhong, et al, ). However, the soil has a great adsorption capacity and straining potential for bacterial cells, which may significantly reduce the concentration of suspended bacterial cells as they transport (Zhong, Liu, et al, ). Rhamnolipids have been widely used to modify surface properties of both bacterial cells and soil particles to weaken bacterial attachment and enhance transport of bacteria in soil.…”

“…Recently, the low concentration of rhamnolipid (lower than CMC) was also reported to facilitate bacterial transport in subsurface for bioaugmentation applications. For example, it was reported that low concentration of rhamnolipid significantly attenuated hydrophobic interactions between P. aeruginosa cells and glass beads, and hence reduced cell adsorption and enhanced cell transport (Zhong, Jiang, et al, ; Zhong, Liu, et al, ). The effect of low‐concentration mono‐rhamnolipid on transport of P. aeruginosa cells in natural porous media (silica sand and a sandy soil) with or without hexadecane as the nonaqueous phase liquid (NAPL) was further investigated in the study of Liu, Zhong, et al (), wherein it was observed that transport of cells in natural porous media was enhanced by rhamnolipid through decreasing bacterial CSH, and the relative enhancement in the presence of NAPL was greater than that in the absence of NAPL.…”