Life processes transform materials available from the environment into cell components. Organic materials are converted to carbon skeletons for monomer and polymer synthesis, as well as being used to supply energy. Microbes synthesize monomers in the proportions needed for growth. This is possible through the regulation of the reactions of anabolism and catabolism. With a few exceptions, microbial ecosystems are oligotrophic with a limited availability of nutrients, the raw materials used for biosynthesis. Furthermore, nutrients are not usually found in balanced concentrations while the organisms have to compete with each other for available nutrients.

Unlike animals and plants, unicellular microbial cells are more directly coupled to their environment, which changes continuously. Many of these changes are stressful so organisms have evolved to cope with this situation. They regulate their metabolism to adapt to the ever-changing environment.

Since almost all biological reactions are catalyzed by enzymes, metabolism is regulated by controlling the synthesis of enzymes and their activity (Table 12.1). Metabolic regulation through the dynamic interactions between DNA or RNA and the regulatory apparatus employed determine major characteristics of organisms. In this chapter, different mechanisms of metabolic regulation are discussed in terms of enzyme synthesis through transcription and translation and enzyme activity modulation.

Mechanisms regulating enzyme synthesis

The rate of biological reactions catalyzed by enzymes is determined by the concentration and activity of the enzymes. Various mechanisms regulating the synthesis of individual enzymes are discussed here before multigene regulation is considered.