Chapter 5: Microbial Metabolism

Enzymes play a central role in these metabolic reactions, and the chapter thoroughly explains their structure, specificity, cofactors, and mechanisms of action. It also discusses how environmental conditions like temperature, pH, and substrate concentration influence enzymatic activity, and how inhibitors—both competitive and noncompetitive—can affect enzyme function. The role of ATP as the primary energy currency is emphasized, with explanations of how it is generated through substrate-level phosphorylation, oxidative phosphorylation, and photophosphorylation. The chapter continues by tracing the key metabolic pathways used by microorganisms to produce energy from glucose: glycolysis, the Krebs cycle (citric acid cycle), and the electron transport chain. Aerobic respiration, which uses oxygen as the final electron acceptor, is compared to anaerobic respiration, which uses alternative acceptors. Fermentation is introduced as a method of ATP production that does not require oxygen or the electron transport chain, with examples like lactic acid and alcoholic fermentation in microbes. The chapter also explores the metabolism of other energy sources, including lipids and proteins, and explains how they are catabolized through pathways that converge with central metabolism. Biosynthetic (anabolic) pathways are described in the context of how microbes build macromolecules such as amino acids, nucleotides, and lipids. Finally, the chapter addresses amphibolic pathways—those that function in both catabolism and anabolism—and how regulation of metabolic pathways allows microbes to respond to changing environmental conditions. This chapter lays the biochemical groundwork for understanding microbial growth, energy production, and the metabolic diversity that makes microorganisms so adaptable across a range of environments.