The influence of certain electrolytes upon the electrical charge of bacteria. 2

Abstract

In connection with an extensive series of studies on the effect of electrolytes upon the various properties of the bacterial cell, we have measured the electrical charge of vegetative cells of B. cereus (chosen on account of its large size) by the direct microscopic method described by Northrop. 3 In conducting these experiments a voltage of known magnitude (112 v.) is applied to non-polarizing zinc-zinc sulphate electrodes and the direction and velocity of migration of the bacteria in unbuffered suspensions determined by observing through the microscope the time taken by the bacterial cells to cross a definite space on the ocular micrometer. In order to avoid theoretical assumptions we have expressed all results in terms of this observed velocity, a high velocity in general presumably signifying of course a greater charge. The average results obtained with varying hydrogen ion concentrations generally based on four or more observations at each P_H value are indicated below.

It appears that these bacteria maintain a fairly high and reasonably consistent negative charge through the wide range of reaction between P_H 5 and P_H 10, rising somewhat with increasing alkalinity. On the acid side of this range the charge drops steadily to an isoelectric point at about P_H 2.0, the charge beyond this point being slight and variable and sometimes reversed. At reactions more alkaline than P_H 10 the charge diminishes even more rapidly to a second (alkaline) isoelectric point at about P_H 12.