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Abstract
In previous studies, successful knock-outs of the lacI gene in various Escherichia coli ( E. coli ) strains was created. Further testing of the MG1655/ Δ lacI strain grown at 30 ˚ C in M9 glycerol minimal media showed wild type basal levels of β -galactosidase production. Potential explanations for such a result could include faulty chromosomal gene alterations, metabolic alterations due to differences in growth phase, or media selection that introduced catabolite repression exclusively to the MG1655/ Δ lacI strain. In this study, a qualitative inspection of growth of wild type and Δ lacI mutant strains of E. coli on various differential and selective plates was used to determine if the strains created in Beamish et al’s study have a faulty chromosome insertion of the kanamycin selection cassette. Quantitative growth and β -galactosidase enzyme activity assays were performed to see if the bacterial growth phase and catabolite repression play a crucial role in the basal β -galactosidase production levels of the MG1655/ Δ lacI mutant. Preliminary data revealed that all strains of Δ lacI mutants showed constitutive β -galactosidase production in the absence of an inducer, contrary to previous findings. The study revealed that catabolite repression and early growth up to four hours in relatively low bacterial density are not responsible for the reported wild type basal level production of β -galactosidase seen in the MG1655/ Δ lacI mutant in the previous study.