In situ growth and activity and modes of penetration of Escherichia coli in unconsolidated porous materials

Abstract

Statistically reliable data on the in situ rates of growth, substrate consumption, and product formation are required to test the validity of the mathematical models developed for microbially enhanced oil recovery and in situ bioremediation processes. A simple, replicable porous-core system that could be aseptically divided into sections at various times was developed to follow the kinetics of microbial growth and metabolism in situ. This core system was used to study the kinetics of growth and the mode of penetration of strains of Escherichia coli through anaerobic, nutrient-saturated, fine Ottawa sand (permeability of 7.0 p.m2 and porosity of 37%) under static conditions. The in situ rate of growth of a wild-type, motile, chemotactic strain, RW262, was two times slower inside cores than it was in liquid cultures. The mode of metabolism of galactose by strain RW262 was not altered inside cores, as acetate was the only product detected either inside the cores or in liquid cultures. Without applied advective force, strain RW262 grew exponentially and moved through cores at a rate of about 0.1 m/day. The cell population moved through cores in a band-like fashion, as the front of the moving cells consisted of high cell concentrations (greater than 105 cells per ml). Until the breakthrough of the cells occurred, galactose consumption and acetate production were observed only in the proximal sections of the core, showing that the cell propagation preceded the complete depletion of the substrate or the accumulation of large amounts of products. A motile, nonchemotactic strain of E. coli (RP5232) penetrated cores faster than did its chemotactic parental strain (RP437), which can be explained by differences in their mode of growth inside the cores. Unlike the wild-type, chemotactic strain RP437, which grew and moved through cores in a band-like fashion, cells of the nonchemotactic strain moved through cores in a diffuse manner, as the front of the moving cells consisted of low cell concentrations (103 cells per ml). The appearance of nonchemotactic cells in a section of the core was not necessarily followed by an increase in cell concentration in that section with time. For the nonmotile strain RP2912, a high cell density (107 cells per ml) in a section of the core was observed before cells were detected in the next section. This suggested that the transport of nonmotile cells through porous material requires a high cell density and may occur by a physical displacement process in which some of the progeny cells are forced into the less populated regions of the core.

The influence of physical heterogeneity on microbial degradation and distribution in porous media

“…The aqueous biomass was significantly attenuated within the pulse interior. Biological processes that could lead to this reduction in aqueous biomass include a reduction in growth in the pulse interior due to oxygen limitations [Jenneman et al, 1985[Jenneman et al, , 1986Reynolds et al, 1989;Sharma et al, 1993] Figure 5c was almost identical to the experimental data, suggesting that the suppression of the electrostatic potential was the dominant process resulting in the decrease in aqueous biomass within the pulse interior.…”

Determination of effective transport coefficients for bacterial migration in sand columns

“…With growing interest surrounding in situ bioremediation as a treatment option for cleaning up contaminated soil, a few experimental studies (18,22,25,26) have been aimed at determining rates of bacterial penetration through porous media. These studies have typically involved measurement of rates, in units of distance per time, which differ depending on the type of soil (physical characteristics and porosity) used.…”

“…López de Victoria (18) studied several subsurface isolates and their chemotactic response toward and/or away from trichloroethylene and noted rate enhancements from 10 m/s to 20 m/s for several strains when a trichloroethylene gradient was established within 30-cm columns filled with topsoil. Sharma et al (26) improved upon this method of determining penetration rates of E. coli by sectioning columns at a given incubation time and determining bacterial density profiles throughout the column. This group concluded that a nonchemotactic E. coli mutant penetrated in a diffusive manner at a faster rate than its chemotactic parent.…”

Characterization of the Microbial Community in the Rhizosphere ofPhragmites australis(Cav.) Trin ex. Steudel Growing in the Sun Island Wetland

“…The authors postulate that the universal microorganisms thriving in all the sampling points have the capacity to give an ecophysiological response to variational habitats in a broad or specific way. Microorganisms, especially the rhizospheric ones, have the potential to alter the properties of the soil with cells or cellular secretions (Degans, 1997;Jing et al, 2007;Sharma et al, 1993). Multiple secondary effects resulted from microbial consumption and production of metabolites, which may influence the solids, water, and atmosphere of given soil environments (Lehman et al, 2004).…”