Bacterial Cells

VAIRO, MARINA L. R. (University of Sao Paulo, Sao Paulo, Brazil) AND WALTER BORZANI. Precise adsorption method for measuring the percentage of dead bacterial cells. Appl. Microbiol. 10: 500-503. 1962.-It was observed that Freundlich's law is obeyed when methylene blue is adsorbed from different aqueous solutions by mixtures of dead and live bacterial cells. A simple and precise colorimetric method was developed for determining the percentage of dead cells. Borzani and Vairo (1960a) proposed a method for the evaluation of the percentage of dead cells in suspensions of Sarcina lutea, based on the fact that, when this percentage is greater than about 40 %, the adsorption of methylene blue by the dead cells follows Freundlich's law. It was also observed (Borzani and Vairo, 1960a) that the described method was not applicable to Bacillus subtilis, Serratia marcescens, and Escherichia coli, because dead and live cells of these microorganisms adsorb practically the same quantity of methylene blue. The purpose of this paper is to show that (i) the convenient choice of the experimental conditions leads to the applicability of Freundlich's law to the adsorption of dye by mixtures of dead and live cells of bacteria other than S. lutea, (ii) the applicability of Freundlich's law is observed when the percentage of dead cells varies from 0 to 100 %, and (iii) the simple and precise method for the measurement of the percentage of dead yeast cells, proposed in a previous paper (Vairo, 1962b), can be applied to some bacteria. This report shows that the adsorption of certain dyes by mixtures of dead and live bacterial cells follows Freundlich's law when the percentage of dead cells varies from 0 to 100 %, and describes a method for the measurement of the percentage of dead bacterial cells. Application of Freundlich's law. The physicochemical law of Freundlich, already mentioned in other papers (Borzani and Vairo, 1958, 1959, 1960b; Vairo, 1962a, 1962b), can be written: C;C= KPC Cfn where Ci is the initial dye concentration, Cf is the concentration at the equilibrium point, C is the cell concentration, and P is the percentage of dead cells; K and n are constants that depend upon the experimental conditions. In this particular case, C is constant and P varies from 0 to 100 %. The previous equation, then, can be written: