BRIDGING THE GAP BETWEEN LABORATORY MICROBIAL ATTACHMENT INVESTIGATIONS AND FIELD MICROCOSM STUDIES

The attachment of a bacterium to the mineral surface initiates a host of bacterially driven geochemical reactions. Once attached, cells can facilitate a series of reactions ranging from the retardation of toxic metals adsorbed to their surfaces, to the accelerated weathering of minerals. Microbes may gain a competitive advantage over planktonic cells when attached through the preferential acquisition of nutrients from the host mineral, protection from predation, and communalism among various microbial species. Attached organisms can enhance or potentially decrease the rate of weathering reactions via the generation of pH gradients, complexation via ligands, and by enhancing the kinetics of secondary mineral phase formation. Therefore to accurately predict and quantify bacterial transport in groundwater systems and the role of bacteria in weathering and diagenetic processes we must first quantify the nature and selectivity of the initial attachment of bacteria to mineral surfaces.

In this investigation, we studied the attachment behavior of the dissimilatory iron reducing bacterium (DIRB) Shewanella putrafaciens as a function of pH, ionic strength, and in the presence of natural groundwaters and macronutrients to the mineral magnetite. We utilized batch attachment studies (after Yee et al., 2000) and electrophoretic mobility data under these conditions to enable the interpretation of attachment of this DIRB in a variety of geological settings. Our results indicate that natural groundwaters and the presence of critical macronutrients dampens the electronectivity of magnetite surface at near-neutral pH increasing which enhances Shewanella putrefaciens attachment affinity in experimental systems