When facultative organisms as examined under the microscopes are grown under aerobic conditions, growth is always more vigorous than that obtained under anaerobic conditions. This is because of the greater amount of phosphate bond energy made available by respiration. (more…)
Catabolite Repression This type of control is frequently observed when organisms are grown on glucose or some other rapidly metabolizable energy source. The catabolite repression results in a repression of synthesis of enzymes that would metabolize the added substrate less rapidly than glucose, this is oftentimes referred to as the glucose effect. When the lac system is induced, the rate of synthesis of beta-galactosidase is considerably reduced in cultures growing upon glucose, compared with cells for which some other metabolite is provided as the carbon source. The addition of cAMP to cultures overcomes glucose repression by stimulating transcription of the inducible enzyme, beta-galactosidase. The level of cAMP in the cell varies with conditions of growth and reflects the energetic needs of the cell. The level is low when the available energy exceeds the biosynthetic requirement for energy and the level of cAMP rises when the carbon supply of the organisms is depleted. The molecular aspects of catabolite repression are presented in. (more…)
Porin These are major proteins uniquely found in the outer membrane and having molecular weights of around 35,000. They form transmembrane pores or diffusion channels that allow passage of small hydrophilic molecules through the outer membrane. Porins also serve as specific attachment sites for phage, vitamin B12, and other nutrients. The structures of porins are better seen using the microscope. The occurrence of some porins is regulated environmentally by the presence or absence of certain substrates. Two classes of porins have been found. Enterobacterial porins exclude molecules greater than 600 daltons, whereas P. aeruginosa and perhaps gonococcal porins exhibit higher cutoff ranges. Porins are known to be mitogenic, indicating that since both LPS and porins act similarly in this respect, the mammalian system is geared to detect either or both components of potentially infectious organisms. (more…)
Mesosomes These membrane-associated organelles are more easily demonstrated in gram-positive than in gram-negative bacteria. Mesosomes are usually seen as cytoplasmic sacs that contain whorled, lamellar, tubular, or vesicular structures and are often associated with division septa. Their compositions are obviously observed when utilizing a microscope in studying them. Attachment of mesosomes to both DNA chromatin and membrane has been demonstrated by thin-section electron microscopy. Formation of protoplasts or spheroplasts results in eversion of tubular or vesicular mesosomal components, which remain attached at one end to the outside of the membrane, whereas the enclosing mesosomal sacs disappear and are apparently pulled into the membrane by the stretched protoplast. These are all clearly viewed using the microscope. Mesosomes have been reported to be artifacts of fixation procedures, but it is difficult to explain vesicular mesomal tubules as artifacts. (more…)
Bacterial cells, like the cells of all living organisms, accomplish work and are seen with microscopy. For this they require a source of energy. Although the wide variety of compounds that serve as a source of energy for microorganisms is almost limitless, there is a remarkable plainness in the basic metabolic patterns utilized to transform this energy into a useful form. Many of these systems are fundamentally similar to those found in the higher forms of life, but superimposed on these basic mechanisms are examples of differentiation unique to the bacterial world. (more…)
The fermentation of glucose is always initiated by a phosphorylation at the expense of ATP, to yield glucose 6-phosphate. The pyretic acid to which glucose 6-phosphate is converted is a key intermediate in the fermentative metabolism of all carbohydrates. In its formation, NAD is reduced and must be re-oxidized in order to achieve a final oxidation-reduction balance. This re-oxidation characteristically occurs in the terminal step reactions and is accompanied by the reduction of a product derived from pyretic acid. This procedure has been observed using a light microscope. Various microscopes such as stereo microscope, electron microscope, scanning electron microscope and other high power microscopes can be used to study the conditions of bacteria under different processes. (more…)