Clip Autosuggest Results Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content +++ ROLE OF METABOLISM IN BIOSYNTHESIS AND GROWTH ++ Microbial growth requires the polymerization of biochemical building blocks into proteins, nucleic acids, polysaccharides, and lipids. The building blocks must either be present in the growth medium or synthesized by the growing cells. Additional biosynthetic demands are placed by the requirement for coenzymes that participate in enzymatic catalysis. Biosynthetic polymerization reactions demand the transfer of anhydride bonds from adenosine triphosphate (ATP). Growth demands a source of metabolic energy for the synthesis of anhydride bonds and for the maintenance of transmembrane gradients of ions and metabolites. ++ Metabolism is composed of two components: catabolism and anabolism (Figure 6-1). Catabolism encompasses processes that harvest energy released from the breakdown of compounds (eg, glucose), and using that energy to synthesize ATP. In contrast, anabolism, or biosynthesis, includes processes that utilize the energy stored in ATP to synthesize and assemble the subunits, or building blocks, of macromolecules that make up the cell. The sequence of building blocks within a macromolecule is determined in one of two ways. In nucleic acids and proteins, it is template-directed: DNA serves as the template for its own synthesis and for the synthesis of the various types of RNA; messenger RNA serves as the template for the synthesis of proteins. In carbohydrates and lipids, on the other hand, the arrangement of building blocks is determined entirely by enzyme specificities. Once the macromolecules have been synthesized, they self-assemble to form the supramolecular structures of the cell, for example, ribosomes, membranes, cell wall, flagella, and pili. ++ FIGURE 6-1 The relationship between catabolism and anabolism. Catabolism encompasses processes that harvest energy released during disassembly of compounds, using it to synthesize adenosine triphosphate (ATP); it also provides precursor metabolites used in biosynthesis. Anabolism, or biosynthesis, includes processes that utilize ATP and precursor metabolites to synthesize and assemble subunits of macromolecules that make up the cell. (Reproduced with permission from Nester EW, Anderson DG, Roberts CE, et al: Microbiology: A Human Perspective, 6th ed. McGraw-Hill, 2009, p. 127. © McGraw-Hill Education.) Graphic Jump LocationView Full Size| Favorite Figure |Download Slide (.ppt) ++ The rate of macromolecular synthesis and the activity of metabolic pathways must be regulated so that biosynthesis is balanced. All of the components required for macromolecular synthesis must be present for orderly growth, and control must be exerted so that the resources of the cell are not expended on products that do not contribute to growth or survival. ++ This chapter contains a review of microbial metabolism and its regulation. Microorganisms represent extremes of evolutionary divergence, and a vast array of metabolic pathways is found within the group. For example, any of more than half a dozen different metabolic pathways may be used for assimilation of a relatively simple compound, benzoate, and a single pathway for benzoate assimilation may be regulated by any of more than half a dozen control mechanisms. Our ... Your Access profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'. Please click ‘Continue’ to continue the affiliation switch, otherwise click ‘Cancel’ to cancel signing in.

+++ INTRODUCTION ++ Cultivation is the process of propagating organisms by providing the proper environmental conditions. Parasites, bacteria, and viruses all generally require cultivation for detailed study. The field of microbiology has the greatest experience in the cultivation of bacteria and as such, this is the focus of this chapter. ++ Bacteria divide by binary fission, asexual reproduction where a single cell divides giving rise to two cells. Those two cells give rise to a total of four cells and so on. This process of replication requires the acquisition of elements that make up their chemical composition. Nutrients from the environment provide these elements in metabolically accessible forms. In addition, organisms require metabolic energy to synthesize macromolecules and maintain essential chemical gradients across their membranes. Factors that must be controlled during growth include the nutrients, pH, temperature, aeration, salt concentration, and ionic strength of the medium. +++ REQUIREMENTS FOR GROWTH ++ Most of the dry weight of microorganisms is organic matter containing the elements carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. In addition, inorganic ions such as potassium, sodium, iron, magnesium, calcium, and chloride are required to facilitate enzymatic catalysis and to maintain chemical gradients across the cell membrane. ++ For the most part, the organic matter is in macromolecules formed by the introduction of anhydride bonds between building blocks. Synthesis of the anhydride bonds requires chemical energy, which is provided by the two phosphodiester bonds in adenosine triphosphate (ATP; see Chapter 6). Additional energy required to maintain a relatively constant cytoplasmic composition during growth in a range of extracellular chemical environments is derived from the proton motive force. The proton motive force is the potential energy that can be derived by passage of a proton across a membrane. In eukaryotes, the membrane may be part of the mitochondrion or the chloroplast. In prokaryotes, the membrane is the cytoplasmic membrane of the cell. ++ The proton motive force is an electrochemical gradient with two components: a difference in pH (hydrogen ion concentration) and a difference in ionic charge. The charge on the outside of the bacterial membrane is more positive than the charge on the inside, and the difference in charge contributes to the free energy released when a proton enters the cytoplasm from outside the membrane. Metabolic processes that generate the proton motive force are discussed in Chapter 6. The free energy may be used to move the cell, to maintain ionic or molecular gradients across the membrane, to synthesize anhydride bonds in ATP, or for a combination of these purposes. Alternatively, cells given a source of ATP may use its anhydride bond energy to create the proton motive force that in turn may be used to move the cell and to maintain chemical gradients. ++ To grow, a bacterium requires all the elements in its organic matter as well as the full complement of ...

TAXONOMY—THE VOCABULARY OF MEDICAL MICROBIOLOGY ++ One has only to peruse the table of contents of this book to appreciate the diversity of medical pathogens that are associated with infectious diseases. It has been estimated that we currently have the capacity to identify a surprisingly small number of the pathogens responsible for causing human disease. In part this is due to our inability to culture or target these organisms using molecular probes. The diversity of even these identifiable pathogens alone is so great that it is important to appreciate the subtleties associated with each infectious agent. The reason for understanding these differences is significant because each infectious agent has specifically adapted to a particular mode(s) of transmission, the capacity to grow in a human host (colonization), and a mechanism(s) to cause disease (pathology). As such, a vocabulary that consistently communicates the unique characteristics of infectious organisms to students, microbiologists, and health care workers is critical to avoid the chaos that would ensue without the organizational guidelines of bacterial taxonomy (Gk. taxon = arrangement; eg, the classification of organisms in an ordered system that indicates a natural relationship). ++ Identification, classification, and nomenclature are three separate but interrelated areas of bacterial taxonomy. Each area is critical to the ultimate goal of accurately studying the infectious diseases and precisely communicating these to others in the field. ++ Identification is the practical use of a classification scheme (1) to isolate and distinguish specific organisms among the mix of complex microbial flora, (2) to verify the authenticity or special properties of a culture in a clinical setting, and (3) to isolate the causative agent of a disease. The latter may lead to the selection of specific pharmacologic treatments directed toward their eradication, a vaccine mitigating their pathology, or a public health measure (eg, handwashing) that prevents further transmission. ++ Identification schemes are not classification schemes, although there may be some superficial similarity. For example, the popular literature has reported Escherichia coli as the causative agent of hemolytic uremic syndrome (HUS) in infants. There are hundreds of different strains that are classified as E. coli but only a few that are associated with HUS. These strains can be “identified” from the many other E. coli strains by antibody reactivity with their O-, H-, and K-antigens, as described in Chapter 2 (eg, E. coli O157:H7). However, they are more broadly classified as a member of the family Enterobacteriaceae. ++ In a microbiologic context, classification is the categorization of organisms into taxonomic groups. Experimental and observational techniques are required for taxonomic classification. This is because biochemical, physiologic, genetic, and morphologic properties are historically necessary for establishing a taxonomic rank. This area of microbiology is necessarily dynamic as the tools continue to evolve (eg, new methods of microscopy, biochemical analysis, and computational nucleic acid biology). ++ Nomenclature refers to the naming of an organism by an established group ...

This chapter discusses the basic structure and function of the components that make up eukaryotic and prokaryotic cells. It begins with a discussion of the microscope. Historically, the microscope first revealed the presence of bacteria and later the secrets of cell structure. Today, it remains a powerful tool in cell biology. +++ OPTICAL METHODS +++ The Light Microscope ++ The resolving power of the light microscope under ideal conditions is about half the wavelength of the light being used. (Resolving power is the distance that must separate two point sources of light if they are to be seen as two distinct images.) With yellow light of a wavelength of 0.4 µm, the smallest separable diameters are thus about 0.2 µm (ie, one-third the width of a typical prokaryotic cell). The useful magnification of a microscope is the magnification that makes visible the smallest resolvable particles. Several types of light microscopes, which are commonly used in microbiology, are discussed as follows. +++ A. Bright-Field Microscope ++ The bright-field microscope is the most commonly used in microbiology courses and consists of two series of lenses (objective and ocular lens), which function together to resolve the image. These microscopes generally employ a 100-power objective lens with a 10-power ocular lens, thus magnifying the specimen 1000 times. Particles 0.2 µm in diameter are therefore magnified to about 0.2 mm and so become clearly visible. Further magnification would give no greater resolution of detail and would reduce the visible area (field). ++ With this microscope, specimens are rendered visible because of the differences in contrast between them and the surrounding medium. Many bacteria are difficult to see well because of their lack of contrast with the surrounding medium. Dyes (stains) can be used to stain cells or their organelles and increase their contrast so that they can be more easily seen in the bright-field microscope. +++ B. Phase-Contrast Microscope ++ The phase-contrast microscope was developed to improve contrast differences between cells and the surrounding medium, making it possible to see living cells without staining them; with bright-field microscopes, killed and stained preparations must be used. The phase-contrast microscope takes advantage of the fact that light waves passing through transparent objects, such as cells, emerge in different phases depending on the properties of the materials through which they pass. This effect is amplified by a special ring in the objective lens of a phase-contrast microscope, leading to the formation of a dark image on a light background

Humans also have an intimate relationship with microorganisms; 50–60% of the cells in our bodies are microbes (see Chapter 10). The bacteria present in the average human gut weigh about 1 kg, and a human adult will excrete his or her own weight in fecal bacteria each year.