Determining the optimal thymidine concentration for growing Thy- Escherichia coli strains

Abstract

Changes of thymidine concentration in the growth medium affect the chromosome replication time of Thy- strains without at the same time causing a detectable difference in the growth rate (R. H. Pritchard and A. Zaritsky, Nature 226:126-131, 1970). Consequently, the optimal thymidine concentration cannot be determined by ascertaining which concentration produces the highest growth rate. Here we present a method for determining the optimal thymidine concentration of any Thy- Escherichia coli strain. Using this method, we found that the E. coli 'wild-type' strain MG1655 has a partial Thy- phenotype.