The cell surface charge of fast-and slow-growing bacteria isolated from a paddy soil.

Abstract

The cell surface charge of 101 strains of bacteria isolated from grassland soil was examined by determining the electrophoretic mobility (EPM) of the cells. The isolates were cultured in diluted nutrient broth medium at 27°C and the EPM of the cells was measured by micro-electrophoresis in 10mM phosphate buffer solution at 25°C as a function of pH varying from 3.1 to 9.0. All the isolates showed negative EPM values at pH 7. These values varied characteristically among strains, i.e., slow-growing isolates showed a lower level of negative EPM values compared with fast-growing isolates. The EPM of each strain did not greatly differ from pH 9 to 6, whereas it showed a lower level of negative values under more acidic conditions. This change in the EPM value was smaller for the slow-growing isolates than that for the fast-growing ones. Under the most acidic condition (pH 3.1), some isolates, mostly the fastest-growing, Gram-positive bacteria, showed positive EPM values. The above detailed changes in EPM suggest that the fast-growing isolates have a greater number of acidic groups at the cell surface, compared with the slow-growing isolates. Furthermore, the finding of positive EPM values for the fastest-growing bacteria indicates the existence of some basic groups at their cell surface.