Abstract
Numerous experiments in this laboratory and elsewhere 1 have shown that all cations in low concentration stimulate, and in higher concentration inhibit, bacterial viability. It has been suggested that the stimulating effect was associated with increased diffusion through the cell wall—the inhibitive effect with decreased diffusion. Shaughnessy and Winslow 2 demonstrated that salt concentrations known to be favorable did show an increase in ammonia in the menstruum surrounding the cells while toxic concentrations showed a reverse effect. No bacterial counts were made in these experiments, however; and the purpose of the present study was to check these earlier results by parallel determinations of bacterial numbers and diffusion products.
Heavy cultures of Esch. coli were washed off in distilled water, from 12-18 hour agar surface growths in Blake bottles, filtered through paper or cotton to remove clumps or agar, and centrifuged twice to remove soluble foreign materials. The washed cells were then divided into 4 portions which were resuspended respectively in distilled water, in 0.05-0.08 Molar NaCl, in 0.8-1.0 Molar NaCl and in 2.0 Molar NaCl. They were allowed to stand in contact with these menstrua for 30 minutes at 37°. The cells were then removed by centrifugation and the ammonia in the menstruum determined by direct Nesslerization after preliminary clarification by the Standard Methods for Water Analysis of the A.P.H.A. with slight modification. This modification consisted of comparing each specimen with a separate set of color standards containing a corresponding amount of clarified NaCl, since it was found that the different concentrations of NaCl employed caused different degrees of interference with normal Nessler color development.
The basic data for 5 experiments are presented in Table I, with computations of rate of ammonia yield per cell per hour based on the mean of the initial and final counts.
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