Changes in Transforming DNA in Pneumococcus

Abstract

DURING the course of an investigation involving the transforming ability of pneumococcal DNA, an interesting correlation was found between the transforming activity of lysates prepared at varying times from the same culture and the number of viable organisms in the culture. Streptococcus pneumoniae, strain Aml, an aminopterin resistant strain derived from strain R36A of Avery et al.¹, was grown first in P medium and then in NS medium in the manner designed to promote competence². At appropriate times, 1.0 ml. aliquots of the culture in NS medium were lysed in the presence of sodium citrate by the addition of sodium deoxycholate, and the DNA was precipitated with ethyl alcohol using sodium hyaluronate as coprecipitant². In one of the experiments to be discussed another aliquot was taken at the same time as that for the lysate, and, after suitable dilution, was plated out in triplicate for a viable count. The lysates were assayed for their transforming activity with respect to resistance to aminopterin by a conventional method², using Str. pneumoniae strain Cl. 3 as the receptor organism.