Metabolic cycles, bacteria

Sulfonamides are used for controlling urinary tract infections, acute and chronic lung infections (norcadiosis), protozoan infections of the nervous system (i.e., toxoplasmosis), and a variety of infections in humans and livestock. Their mode of activity is by inhibiting the multiplication of bacteria by competitively inhibiting para-aminobenzioc acid (PABA) in the folic acid metabolism cycle (O Neil et al., 2001). More specifically, they block the synthesis of folic acid in bacteria as the drugs are structurally similar to PABA. Folic acid is essential to the synthesis of amino acids and nucleic acids. In bacteria, folic acid is synthesized from PABA... 

The glyoxylate cycle enhances the metabolic versatility of many plants and bacteria. This cycle, which uses some of the reactions of the citric acid cycle, enables these organisms to subsist on acetate because it bypasses the two decarboxylation steps of the citric acid cycle. 

Metabolic Cycles in the Fermentation by Propionic Acid Bacteria... 

Physiological Role of Citric Acid. Citric acid occurs ia the terminal oxidative metabolic system of virtually all organisms. This oxidative metabohc system (Fig. 2), variously called the Krebs cycle (for its discoverer, H. A. Krebs), the tricarboxyUc acid cycle, or the citric acid cycle, is a metaboHc cycle involving the conversion of carbohydrates, fats, or proteins to carbon dioxide and water. This cycle releases energy necessary for an organism s growth, movement, luminescence, chemosynthesis, and reproduction. The cycle also provides the carbon-containing materials from which cells synthesize amino acids and fats. Many yeasts, molds, and bacteria conduct the citric acid cycle, and can be selected for thek abiUty to maximize citric acid production in the process. This is the basis for the efficient commercial fermentation processes used today to produce citric acid. 

The processes of electron transport and oxidative phosphorylation are membrane-associated. Bacteria are the simplest life form, and bacterial cells typically consist of a single cellular compartment surrounded by a plasma membrane and a more rigid cell wall. In such a system, the conversion of energy from NADH and [FADHg] to the energy of ATP via electron transport and oxidative phosphorylation is carried out at (and across) the plasma membrane. In eukaryotic cells, electron transport and oxidative phosphorylation are localized in mitochondria, which are also the sites of TCA cycle activity and (as we shall see in Chapter 24) fatty acid oxidation. Mammalian cells contain from 800 to 2500 mitochondria other types of cells may have as few as one or two or as many as half a million mitochondria. Human erythrocytes, whose purpose is simply to transport oxygen to tissues, contain no mitochondria at all. The typical mitochondrion is about 0.5 0.3 microns in diameter and from 0.5 micron to several microns long its overall shape is sensitive to metabolic conditions in the cell. 

There are several examples in which metabolites that toxify the organism responsible for their synthesis are produced. The classic example is fluoroacetate (Peters 1952), which enters the TCA cycle and is thereby converted into fluorocitrate. This effectively inhibits aconitase—the enzyme involved in the next metabolic step—so that cell metabolism itself is inhibited with the resulting death of the cell. Walsh (1982) has extensively reinvestigated the problan and revealed both the complexity of the mechanism of inhibition and the stereospecihcity of the formation of fluorocitrate from fluoroacetate (p. 239). It should be noted, however, that bacteria able to degrade fluoroacetate to fluoride exist so that some organisms have developed the capability for overcoming this toxicity (Meyer et al. 1990). 

Kertesz MA (1999) Riding the sulfur cycle—metabolism of sulfonates and sulfate esters by Gram-negative bacteria. EEMS Microbiol Rev 24 135-175. 

Nothing seems to be known as yet of the metabolic regulation of enzymes of poly(3HB) producing bacteria that catalyze the last step of the poly(3HB) cycle, i. e., the activation of acetoacetate (Fig. 1, steps 9,10). Since both enzymes are involved in a catabolic sequence, it may be speculated that they are inhibited, for... 

In some ways it is surprising that aerobic bacteria have not made more use of zinc, internally, and calcium generally, especially in controls since we know they present no redox threat and we shall see that their uses increase dramatically in eukaryotes. The aerobic bacteria do have genetic connections for controlling zinc (e.g. the transcription factor ZUR and ZntR genes) but its use is not extensive. The absence of full use of Ca and Zn may well be due to the limited space and the fast time of the bacterial cell metabolism and life cycle. 

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