IN-SITU GROWTH AND ACTIVITY AND MODES OF PENETRATION OF ESCHERICHIA-COLI IN UNCONSOLIDATED POROUS MATERIALS

Statistically reliable data on the in situ rates of growth, substrate consumption, and product formation are required to test the validity o f the mathematical models developed for microbially enhanced oil recov ery 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 me tabolism in situ. This core system was used to study the kinetics of g rowth and the mode of penetration of strains of Escherichia coli throu gh anaerobic, nutrient-saturated, fine Ottawa sand (permeability of 7. 0 mum2 and porosity of 37%) under static conditions. The in situ rate of growth of a wild-type, motile, chemotactic strain, RW262, was two t imes slower inside cores than it was in liquid cultures. The mode of m etabolism of galactose by strain RW262 was not altered inside cores, a s acetate was the only product detected either inside the cores or in liquid cultures. Without applied advective force, strain RW262 grew ex ponentially 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 fro nt of the moving cells consisted of high cell concentrations (greater than 10(5) cells per ml). Until the breakthrough of the cells occurred , galactose consumption and acetate production were observed only in t he proximal sections of the core, showing that the cell propagation pr eceded 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 str ain (RP437), which can be explained by differences in their mode of gr owth inside the cores. Unlike the wild-type, chemotactic strain RP437, which grew and moved through cores in a band-like fashion, cells of t he nonchemotactic strain moved through cores in a diffuse manner, as t he front of the moving cells consisted of low cell concentrations (10( 3) cells per ml). The appearance of nonchemotactic cells in a section of the core was not necessarily followed by an increase in cell concen tration in that section with time. For the nonmotile strain RP2912, a high cell density (10(7) cells per ml) in a section of the core was ob served 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.