You are here:
Sensitivity of Geoelectrical Measurements to the Presence of Bacteria in Porous Media
Citation:
Abdel Aal, G. Z., E. A. Atewana, S. Rossbach, AND D. D. WERKEMA. Sensitivity of Geoelectrical Measurements to the Presence of Bacteria in Porous Media. Journal of Geophysical Research: Biogeosciences. American Geophysical Union, Washington, DC, 115:1-11, (2011).
Impact/Purpose:
Microorganisms are ubiquitous and exist in the subsurface environment as plankton cells or adhered to mineral surfaces of porous media with abundance varying according to the availability of organic matter, water and nutrients [Hazen, 1991; Balkwill and Boone, 1997; Konhauser, 2007]. The microbial cells have distinct electrical properties that probably influence geoelectrical measurements (e.g. the effect of attachment-detachment of bacteria on mobility and zeta potential). It is known that microbial surfaces can develop a significant net surface charge, as a result of protonation/deprotonation of carboxylates, phosphates or other functional groups in their cell envelope [Evgeny et al., 2000]. The net surface charge of bacterial cells results in the formation of an electric double layer, which is subjected to polarization when an electric current is applied. It has been recognized that the ion selectivity of the outer membrane of live bacterial cells in solution can generate a large polarization at low frequencies (<1000 Hz) [Prodan et al., 2004, 2008].
Description:
We investigated the sensitivity of low frequency electrical measurements (0.1-1000 Hz) to (i) microbial cell density, (ii) live and dead cells, and (iii) microbial attachment onto mineral surfaces of clean quartz sands and iron oxide coated sands. Three strains of Pseudomonas aeruginosa PAO1 (wild type, rhlA and pilA mutants) with different motility and attachment properties were used. Varying concentrations of both live and dead cells of P. aeruginosa wild type in sand columns showed no effect on the real conductivity (o') component. However, the imaginary conductivity component (o") increased linearly with increasing concentrations of live cells in sand columns whereas; minimal changes were observed with different concentrations of dead cells. The rhlA mutant of P. aeruginosa showed a higher rate of attachment (K,att) to sand grain surfaces concurrent with a higher o" magnitude, followed by the wild type and pilA mutant. The K,att and corresponding o" values were greater in columns with iron oxide coated sands compared to clean quartz sands. The o" (at 10 Hz) showed a linear and direct correlation with microbial cell density as well as K,att. Minimal changes were observed on the o' due to the attachment of P. aeruginosa cells onto sands. We relate the measured low frequency electrical responses to (i) the distinct electrical properties of live cells and (ii) the density of attached cells to mineral surfaces. The information obtained from this study enhances our interpretation of microbially induced geoelectrical responses in biostimulated geologic media and may have implications for microbial transport studies.