THE CELL SURFACE CHARGE OF FAST- AND SLOW-GROWING BACTERIA ISOLATED FROM A PADDY SOIL

In this study, the cell surface charge of 109 strains of the bacteria isolated from a paddy soil, which showed a wide range of growth rates (0.7-15.1 h doubling time), were examined. As found in the case of grassland-soil bacteria previously (Morisaki, H., Kasahara, Y., and Hattori, T., J. Gen. Appl. Miclobiol., 39, 65-74, 1993), among the strains, fast-growing isolates showed a greater level of negative charge at the cell surface at pH 7.0 compared with the slow-growing isolates. To determine the pH-dependence, the cell surface charge was measured as a function of pH varying from 2.4 to 9.0. Under acidic conditions (below pH 4.0), the negative cell- surface charge became lower. At the most acidic condition (pH 2.4) 34 out of 40 strains of the fast-growing bacteria showed a positive surface charge. This change in the cell surface charge caused by pH-shift from neutral to acidic condition, which was considered to be because charged functional groups (weak acids such as carboxylic acid) existing or exposed at the cell surface lost their negative charge, was greater for the fast-growing isolates than that for the slow-growing ones.