Effect of certain electrolytes on the buffering power of bacterium coli. 1

In the present studies we have developed a technique for the measurement of the power of the bacterial cell to combine with hydrogen and hydroxyl ions. The bacteria show a general tendency to simulate amphoteric colloids and we have therefore measured their amphoteric property by the use of titration curves. A bacterial suspension in water or in a particular salt solution is titrated electrometrically with hydrochloric acid and with sodium hydroxide and similar titration curves are obtained for the menstruum alone. From these two sets of curves it is possible to calculate a series of “buffer ratios” by taking the quotients of the amounts of acid or alkali added to shift the P_H one unit in the bacterial suspension and in the menstruum alone. Such buffer ratios have been calculated for each P_H unit zone between P_H 2 and P_H 12. The titration cells which have been developed for these experiments are illustrated in the accompany figure. The buffer ratios for Bact. coli in distilled water, 0.725, M NaCl, 0.145 M CaCl₂ and in 0.580 M NaCl + 0.145 M CaCl₂ solutions are presented in Table I.

Our findings may be summarized in the following categorical manner:

1. In distilled water suspensions of Bacterium coli show a marked tendency to resist a change in hydrogen-ion concentration in the zones of P_H which are of physiological interest, i. e., P_H 4-10. In more acid and more alkaline solution this buffering power is weaker and the buffer ratios approximate unity at P_H 3-4 and at P_H 10-11.