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A quantitative understanding of microorganism migration in geological formations is critical to predict the dissemination of microorganisms in the environ ment and to evaluate the efficacy of microbially mediated in situ pollutant degradation. The key event that retards the movement of microorganisms in the saturated zone with respect to the convective water flow is the interaction between microorganisms and the matrix surfaces. This interaction may result in adhesion and concomitant retardation. Interactions are determined by the surface thermodynamics of the microorganism and the matrix. Whereas the nature of the matrix substratum surface may be considered temporally invariant, the nature of bacterial cell surfaces is a function of its physiological state. The work presented here explored quantitatively the impact of the physiological state of Pseudomonas aeruginosa Olin on its surface thermodynamic characteristics and its adhesion to dolomite. Lewis acid/base (hydrophobic), Lifshitz−van der Waals (electrodynamic), and Coulombic (electrostatic) forces were measured via contact angle measurements and electrophoretic mobility assays. It was found that P. aeruginosa Olin exhibited a decreased electron-donating potential (γi -) and increased ζ-potential in the stationary phase as compared with logarithmic growth and decay phases. These changes in surface thermodynamic properties were clearly manifested in subsequent partitioning experiments with dolomite. P. aeruginosa Olin was found to partition onto dolomite to a significantly larger extent in the stationary phase than in the logarithmic growth or decay phases. This observation further corroborates the need to include Lewis acid/base interactions in the evaluation of bacterium/surface interactions. The reported results indicate the clear impact of physiological state on surface thermodynamics and adhesion.

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