The Role of Glycerol and Isopropyl Thiogalactoside in Escherichia coli Growth and Lactose Induction of ß-Galactosidase

Enzyme induction was studied by performing β -galactosidase activity assay on a culture of Escherichia coli K-12 wild-type strain B23 induced by IPTG in the presence and absence of lactose. Our findings suggest that lactose-only media supported a slower growth than glycerol-containing media did. Furthermore, lactose was found to have no effect on Escherichia coli growth in glycerol, whereas its analogue, isopropyl thiogalactoside, negatively influenced growth. In terms of β -galactosidase activity, lactose and isopropyl thiogalactoside were also found to exert different effects. Lactose in the absence of IPTG appeared to be the stronger inducer, yielding a higher enzyme activity. Interestingly, the addition of both lactose and isopropyl thiogalactoside decreased enzyme activity to a minimal level.