Summary: The force necessary to remove the cells of a bacterium, an isolate (Bacillus sp.) from grassland soil, from a quartz plate was investigated in phosphate buffer solution by using a well-defined liquid flow caused by electroosmosis. The cells were not removed at a specific strength of removal force but removed over a wide range of force, about 10−14-10−12 N per cell. An exponential relation was observed between the removal force and the number of removed cells in media of pH 7·0,80 and 9·0; more cells were removed by a smaller force. Experiments in media of different pH values in the range 3·0 to 9·0 showed that greater force was necessary to remove the cells in media of lower pH. The smaller electrostatic repulsion between the bacterial cells and the quartz plate at lower pH values was considered to result in the greater force needed for removal. The relation between the strength of the removal force and the strength of the adhesion force of the bacterial cells was considered. The findings showed that the cell adhesion was reversible and that the adhesion site was located near the end of the cell.
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