Ten strains of Rhizobium meliloti and two non-rhizobial strains, Escherichia coli JM105 and Comamonas testosteroni B-356, were studied for their behaviour in soil and water matrices by determining their hydrophobicity, as measured by bacterial adherence to n-octane, and adhesion, as measured by their retention on sandy soil particles. The hydrophobicity values for the rhizobial strains were similar to that for E. coli (around 15%). whereas C. testosteroni, which belongs to the Pseudomonads group, showed a significantly higher level (33%). Both non-rhizobial strains, however, showed higher levels of adhesion, (85% and 78%, respectively) than did the rhizobial strains ( approximate to 55%). The cell surface properties of the rhizobial strains were influenced by the composition of the growth media used, being significantly higher with nutrient-rich media. The nature or level of contaminants in the soil from which these strains were originally isolated did not, however, influence these properties. These characteristics are important in determining the fate of bacteria in the unsaturated subsurface soil environment because of their influence on the vertical transport, distribution and survival. Information about these characteristics will be particularly useful in choosing strains for agricultural applications (e.g., as biofertilizers or biocontrol agents) or in situ soil environmental operations (e.g., bioaugmentation for bioremediation of pollutants). (C) 2001 Elsevier Science Ltd. All rights reserved.