The Time Course of β-Galactosidase Induction in Escherichia coli

Bacteria can vary their enzymic composition markedly when grown in different conditions. In particular, specific enzymes required to utilize a given carbon or nitrogen source are usually only present when they are essential for growth. Such enzymes are known as inducible . In contrast, some enzymes that are normally present in actively growing cells may under certain conditions, especially if the product of their reaction(s) is present in excess in the growth media, be absent or present only in barely detectable amounts. Such enzymes are known as repressible . Naturally certain enzymes are present in cells, in variable amounts, regardless of growth conditions. These enzymes are known as constitutive . This ability to regulate the levels of enzymes in response to different growth conditions enables bacteria to maximize their resourses by only synthesizing enzymes when they are actually needed to support cell maintenance and growth.