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J Bacteriol. 1969 March; 97(3): 1062-1068
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Change in the Absorbancy of Bacterial Suspensions Before Initiation of Growth

Unilever Research Laboratory, Sharnbrook, Bedford, England

ABSTRACT

The apparent absorbancy of suspensions of stationary-phase cells of Streptococcus lactis strain 354/07 decreased immediately after being placed in fresh media. This optical effect also occurred in defined mixtures of buffer glucose and KCl. CaCl₂ caused the absorbancy to increase. CaCl₂ and KCl together had about the same effect as KCl alone. SrCl₂ could replace CaCl₂, but it was less effective by a factor of 10². MnCl₂, MgCl₂, and NaCl were without effect. The absorbancy did not change when cells were first killed by p-chloromercuribenzoate or when the reaction was carried out at 0 C. The rate of the reaction was dependent on temperature and concentration of glucose and salts. Gradient centrifugation suggests that this optical effect was caused by change in the refractive index of the test organism rather than by change in volume. Nine other organisms representing four additional genera gave the same optical effect as S. lactis 354/07. Two other organisms reacted feebly whereas another strain of S. lactis reacted in the opposite way, the absorbancy of the suspension increasing instead of decreasing. Spores of Bacillus cereus did not respond.

¹ Present address: Microbiology Division, Food and Drug Directorate, Tunney's Pasture, Ottawa 3, Canada.