Variation of Surface Charge Density in Monoclonal Bacterial Populations:  Implications for Transport through Porous Media

Abstract

The forced convection of a monodisperse, monoclonal suspension of bacteria through a uniform, saturated porous medium has been investigated. Bench-scale column studies were carried out to measure the removal of microorganisms from suspension due to attachment to the surfaces of the solid phase. The columns were packed with 40-μm borosilicate glass beads, and bacterial sorption was measured as a function of depth in the column using a leucine radiolabel assay. The strains A1264 and CD1 were examined separately. Colloid filtration theory was used to interpret the data, and the average, or effective, affinity of the bacteria for the glass beads was found to decrease with distance traveled through the column. It is postulated that, under these circumstances, the cell/collector affinity (that is, the collision efficiency α) varied due to intrapopulational differences in bacterial surface characteristics. A simple bimodal probability density function, consisting of two Dirac delta functions, was found to satisfactorily represent the α distribution in the original bacterial population. This form of the distribution function was supported by capillary electrophoresis measurements on the bacteria, which showed intrapopulational differences in the surface charge density under the conditions of the transport experiments. These variations in surface charge density are significant inasmuch as they give rise to substantial differences in the colloidal interaction potentials and, presumably, large differences in cell affinity for negatively charged collectors such as glass beads or quartz.

Transport of multiple Escherichia coli strains in saturated porous media

“…Our results are consistent with Simoni et al (1998), Baygents et al (1998), Redman et al (2001a,b), Li et al (2004) and Tufenkji andElimelech (2004b, 2005b), who also reported a reduction of the sticking efficiency with transport distance. In some cases, those variable bacteria deposition rates were likely caused by variation in the LPS coating surrounding the bacteria cells, leading to heterogeneous interaction (Simoni et al, 1998), or by variability in surface charge densities within a bacteria population (Baygents et al;1998, van der Mei and Busscher, 2001, Tufenkji and Elimelech, 2004b.…”

“…In some cases, those variable bacteria deposition rates were likely caused by variation in the LPS coating surrounding the bacteria cells, leading to heterogeneous interaction (Simoni et al, 1998), or by variability in surface charge densities within a bacteria population (Baygents et al;1998, van der Mei and Busscher, 2001, Tufenkji and Elimelech, 2004b. Our results indicated that these transport distance dependent sticking efficiency reductions were caused by the variable presence of motile cells and Ag43 expression: highly motile cells, expressing the Ag43 adhesin were removed faster than cells expressing only one of the two or neither one.…”

“…A characteristic of the classical theory is the use of the sticking efficiency, which is defined by the ratio of the number of particles that strike and stick to a collector to the number of particles striking a collector and is mainly determined by electro-chemical forces between the colloid and surface of the collector. Contrary to the classical theory, research results over the last two decades have indicated that the sticking efficiency of a biocolloid population is not a constant, and the variations have been attributed to variable cell surface properties of individual members of the population, resulting in differences in affinity for collector surfaces (Albinger et al, 1994;Baygents et al, 1998;Simoni et al, 1998;Li et al, 2004;Tufenkji and Elimelech, 2005a;Tong and Johnson, 2007; Foppen et al., 2007a,b). The variation of the deposition rate coefficient has been attributed to a number of reasons, including geochemical heterogeneity on collector grain surfaces (Johnson and Elimelech, 1996;Bolster et al, 2001;Loveland et al, 2003;Foppen et al, 2005), straining (Bradford et al, 2002 andBradford and Bettahar, 2005; Foppen et al, 2007a,b), and heterogeneity of the colloid population due to variability in surface properties (Albinger et al,1994;Baygents et al, 1998.;Simoni et al, 1998;Li et al, 2004; Tufenkji and Elimelech, 2005a,b;Tong and Johnson, 2007).…”

“…However, recent research shows that the deposition rate coefficient is not a constant (Albinger et al, 1994;Baygents, 1998;Simoni et al, 1998;Li et al, 2004;Tufenkji and Elimelech, 2005a,b;Tong and Johnson, 2007;Foppen et al, 2007). The variation of the deposition rate coefficient has been attributed to a number of reasons, including geochemical heterogeneity on collector grain surfaces (Johnson and Elimelech, 1996;Bolster et al, 2001;Loveland et al, 2003;Foppen et al, 2005), straining (Bradford et al, 2002 andBradford and Bettahar, 2005;Foppen et al, 2007a), and heterogeneity of the colloid population due to variability in surface properties (Albinger et al,1994;Baygents et al, 1998.;Simoni et al, 1998;Li et al, 2004;Tufenkji and Elimelech, 2005a,b;Tong and Johnson, 2007;Foppen et al, 2007). The variability in bacteria surface properties has been attributed to variations in lipopolysaccharide (LPS) coating (Simoni et al,1998), distribution of the interaction potential within the bio-colloid population (Li et al, 2004), variations in surface charge densities (Baygents et al,1998;Tufenkji and Elimelech, 2004b), and differences in energy needed to overcome the energy barrier (Tufenkji and Elimelech, 2004b).…”

Processes in Microbial Transport in the Natural Subsurface

“…Most often, however, it is interpreted as reflecting variability in the cell surface properties within a monoclonal bacterial population [1,12,29,110], which would cause the more ''sticky'' bacteria to attach rapidly at short travel distances while a smaller sub-population with less propensity for attachment transports much farther. Baygents et al [10] and Glynn et al [46] observed a bimodal distribution of surface charge density in selected bacterial strains, providing experimental support for this hypothesis. Redman et al [95,96] proposed a multiscale (fractal) distribution of filtration length scales arising from microscale heterogeneity in surface properties of microbes and collectors, and provided experimental support for the model based on column experiments of virus transport.…”