Influence of extracellular polymeric substances on Pseudomonas aeruginosa transport and deposition profiles in porous media

The impact of cell surface extracellular polymeric substances (EPS) on bacterial transport and retention profiles was investigated in saturated columns packed with glass beads. Three genetically well-defined isogenic Pseudomonas aeruginosa strains with different EPS secretion capability and EPS composition were used to systematically examine their deposition behavior over a range of solution chemistry. The presence of EPS on nonmucoid strain PAO1 and mucoid strain PDO300 significantly increased bacterial adhesion over the EPS deficient PAO1 psl pel mutant strain despite their similar surface charge as indicated by the zeta potential measurements. Retained bacterial profiles show the deposition rate coefficients with various shapes and degrees of deviation from those expected from the classic filtration theory. Non-monotonic deviations from the log-linear deposition pattern with the majority of the bacteria retained downgradient of the column inlet were observed when bacterial cells were encapsuled by EPS under both high and low ionic strength conditions. In contrast, the EPS-deficient strain exhibited monotonic deviation from theory only under low ionic strength conditions. The results demonstrate that the non-monotonic deviation from filtration theory observed in this study was driven by steric interactions between extracellular polymers and glass beads. Analysis of the retained polysaccharides (carbohydrates and uronic acids) and protein profiles suggests that bacterial re-entrainment and re-entrapment may have contributed to the downgradient movement of the maximum retained bacteria. The detachment of bacteria may leave behind various constituents of EPS as their "footprints," which can be a valuable tool for tracking the trajectory of bacterial transport.