Effect of iso-propyl-thio-beta-D-galactoside concentration on the level of lac-operon induction in steady state Escherichia coli.

In steady state E. coli cells growing at their maximal rate in broth, maximum induction of beta-galactosidase occurs at 0.10 mM isopropyl-thio-beta-D-galactoside (IPTG). Although induction of lac is near zero in steady state cells that are growing in 0.01 mM IPTG, induction at mildly subdued levels persists down to at least 0.001 mM in post-steady state cultures. Meanwhile, thiogalactoside transacetylase remains uninduced over the full range in which the cells are in steady state.