Effects of Outer Membrane Protein TolC on the Transport of Escherichia coli within Saturated Quartz Sands

Abstract

The outer membrane protein (OMP) TolC is the cell surface component of several drug efflux pumps that are responsible for bacterial resistance against a variety of antibiotics. In this research, we investigated the effects of OMP TolC on E. coli transport within saturated sands through column experiments using a wide type E. coli K12 strain (with OMP TolC), as well as the corresponding transposon mutant (tolC∷kan) and the markerless deletion mutant (ΔtolC). Our results showed OMP TolC could significantly enhance the transport of E. coli when the ionic strength was 20 mM NaCl or higher. The deposition rate coefficients for the wild type E. coli strain (with OMP TolC) was usually >50% lower than those of the tolC-negative mutants. The measurements of contact angles using three probe liquids suggested that TolC altered the surface tension components of E. coli cells and lead to lower Hamaker constants for the cell-water-sand system. The interaction energy calculations using the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory suggested that the deposition of the E. coli cell primarily occurred at the secondary energy minimum. The depth of the secondary energy minimum increased with ionic strength, and was greater for the TolC-deletion strains under high ionic strength conditions. Overall, the transport behavior of three E. coli strain within saturated sands could be explained by the XDLVO calculations. Results from this research suggested that antibiotic resistant bacteria expressing OMP TolC could spread more widely within sandy aquifers.

Comparison of the transport of Bacteroides fragilis and Escherichia coli within saturated sand packs

“…Hydrodynamic dispersion of colloid-sized particles (such as the bacterial cells) has been previously shown to be negligible for uniform sands such as were used in this experiment [17,18]. To facilitate the comparison of the mobility of E. coli and B. fragilis within the saturated sand packs, the clean-bed deposition rate coefficients (k d ), which measure the rates at which bacterial cells were being removed from the aqueous phase under pristine conditions (i.e., the sand surfaces are free of bacterial cells), were estimated from the early cell breakthrough concentrations in the effluent [24][25][26]:…”

“…The B. fragilis cells were then harvested through centrifugation (4000 g, 10 min, 4 • C). The fresh bacterial pellets were rinsed 4 times using the appropriate electrolyte solution to remove the growth media [17,18].…”

Blocking effect of colloids on arsenate adsorption during co-transport through saturated sand columns

“…But, at pH 9.8, soil colloid was difficult to deposit into the primary energy minimum due to the high primary energy barrier (>250 kT). The retention of the soil colloids at pH 9.8 possibly occurred mainly through their entrapment within the secondary energy minimum (Feriancikova et al, 2013;Wang et al, 2011b), where the soil colloid is easily removed by kinetic energy of diffusing (Fig. 4b).…”

D‐Amino acids inhibit initial bacterial Adhesion: Thermodynamic evidence

“…where, z B and z G are the zeta potential of bacteria surfaces (B) and quartz sands (G), respectively. Due to Born repulsion, y 0 , the minimum equilibrium cut-off distance between bacterial cells and the collector, equals 0.157 nm in previous work (Feriancikova et al, 2013). R is the cell radius, and h is the separation distance between the cell and the solid surface.…”

“…Initial bacterial adhesion is generally determined by the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory, which is expressed as the sum of Lifshitz–van der Waals interactions and electrostatic interactions (Feriancikova et al, ). The classical DLVO theory was projected to describe the stability of colloidal suspensions.…”