MICROBIOLOGY Study Guide - 2012

CHAPTER 9. PHYSIOLOGY OF MICROORGANISMS

Microbial physiology studies life Functions based on continuous METABOLISM, which consists of two interrelated processes: assimilation (anabolism) and dissimilation (Catabolism). Anabolic reactions lead to the synthesis of new cellular components, whereas catabolic reactions result in The formation of low-molecular-weight compounds. Some of these compounds serve as precursors for The Biosynthesis of Cell components and enter anabolic pathways, while others are unused by The Cell and excreted into the environment.

To sustain metabolic processes, microorganisms require Energy Sources and nutrients. Microbial energy sources include the electromagnetic energy of light (physical energy) and the energy of oxidation-reduction reactions (chemical energy). The Essence of oxidation-reduction reactions lies in The transfer of electrons from compounds capable of being oxidized (electron Donors) to molecules capable of accepting electrons and thereby being reduced (electron acceptors). Prokaryotes are known to obtain energy through Three Main Mechanisms: Fermentation, Respiration, and Photosynthesis. During fermentation, certain oxidation-reduction reactions result in the formation of compounds whose phosphate groups contain a high amount of Free energy. The corresponding enzyme transfers this phosphate group to ADP, leading to the formation of ATP. The release of energy in the form of ATP during specific fermentation-coupled oxidation-reduction reactions is known as substrate-level phosphorylation.

Various prokaryotes can generate energy via respiration. During The oxidation of organic substances, electrons are transferred along the Respiratory Electron Transport chain, which in many cases leads to the reduction of molecular oxygen to H₂O and the synthesis of ATP. Here, the release of energy in the form of ATP molecules is referred to as Oxidative Phosphorylation. The generation of ATP during photosynthesis is called photosynthetic phosphorylation.

The energy released during respiration and photosynthesis is stored across membranes in the form of the electrochemical proton motive force of hydrogen ions (Δμ_H⁺). In this case, chemical energy is converted into electrochemical energy and can subsequently be utilized for ATP synthesis.

9.1. MICROBIAL ENZYMES

In bacterial Cells, metabolic processes are catalyzed by specific Enzymes. Much like the cells of higher organisms, a microbial cell is equipped with a highly active enzymatic apparatus representing all six known classes of enzymes.

Despite The small size of a bacterial cell, the Intracellular Distribution of enzymes is strictly ordered. Enzymes responsible for Energy Metabolism and nutrient transport are localized in the cytoplasmic membrane (CM) and its derivatives. Protein Synthesis enzymes are associated with Ribosomes. Many Other Enzymes are not bound to specific structures and reside freely in the Cytoplasm.

Some cytoplasm-localized enzymes function independently of one another, whereas others are closely linked, ensuring that metabolic reactions proceed in a precise sequence. Intracellular enzymes that are structurally and functionally integrated form multienzyme complexes, such as respiratory enzymes.

Bacterial Cells also contain lytic enzymes. Responsible for Cell Division and autolysis, they are localized in The Cell wall. The processes of cell wall lysis and biosynthesis occur concurrently with bacterial GROWTH AND DEVELOPMENT, with cell lysis taking place only at late developmental stages. Lytic enzymes of bacterial spores are activated during sporulation and spore germination.

Bacterial enzymes are subdivided into exoenzymes and endoenzymes. Endoenzymes are found exclusively inside the cell, catalyzing biosynthetic and energy-yielding reactions. Exoenzymes are secreted into the external environment to carry out extracellular Digestion. Their function is to catalyze the Hydrolysis of complex Organic compounds into simpler ones that can be readily utilized by the microbial cell. These include Enzymes of the hydrolase Class. Certain exoenzymes perform defensive functions; for instance, penicillinase, secreted by some Bacteria, renders the cell invulnerable to this antibiotic.

Depending on the conditions of their synthesis, Enzymes are classified as constitutive or inducible.

Constitutive enzymes are those synthesized by the cell regardless of the presence of the substrate on which the bacteria are growing. Glycolytic enzymes, for example, fall into this category.

Inducible enzymes are synthesized only in response to the presence in the environment of a specific substrate required by the cell—an inducer. The inducer interacts with the repressor, inactivating it, which in turn activates the cell's genetic apparatus and initiates the Synthesis of the corresponding enzyme. Inducible enzyme synthesis continues as long as the inducer remains present in the medium. The majority of hydrolytic enzymes are inducible.

Alongside processes that induce enzyme synthesis, cells also undergo enzyme suppression, or repression. Depending on The Nature of the repressor, Two Types of repression are distinguished: end-product repression and catabolite repression. In addition to end-product repression, another regulatory mechanism known as catabolite repression occurs. The presence of glucose and certain other readily utilized sources of carbon and energy in the medium leads to the repression of many inducible enzymes. Specifically, glucose represses the synthesis of β-galactosidase even when the enzyme's inducer, lactose, is present in the medium. Catabolite repression can be viewed as an adaptive mechanism enabling the microbial cell to preferentially utilize readily available energy sources.

In addition to metabolic enzymes, pathogenic bacteria possess so-called aggressiveness enzymes, which act as virulence factors. These include deoxyribonuclease, neuraminidase, collagenase, and hyaluronidase. The latter degrades hyaluronic acid, a major component of the Extracellular matrix in Connective Tissue.

Microbial enzymes are widely utilized in the food industry, microbiological industry, and medicine. Producers of these enzymes include bacteria, Yeasts, and filamentous Fungi. Proteolytic Enzymes are used in cottage cheese production and cheesemaking; pectolytic enzymes are employed to accelerate juice extraction from fruits and berries and to clarify juices; and amylolytic enzymes have found broad application in brewing, the alcohol industry, and baking. Microbial enzymes such as Restriction Endonucleases and ligases are indispensable tools in Introduction/32.html">Genetic Engineering.

The Application of Enzymes across various Branches of the food industry significantly accelerates technological processes and increases both the yield and quality of the final products.