High Power Microscopes and Bacteria Membranes
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.
In gram-negative cells, points of connection between membrane and wall, known as adhesion sites or Bayer junctions, occur. The Bayer junctions are physiologically active. Externally, they appear to be sites of bacteriophage DNA injection and complement-mediated lysis. Internally, they appear to be growth zones where they serve as sites for translocation of secretory protein, outer membrane proteins and lipopolysaccharides, and capsular polysaccharides. Sex pili as well as flagella also emerge from the cell at fusion sites between inner and outer membranes. The different kinds or types of microscopes such as the light microscope, binocular microscope, stereo microscope, high-powered microscope and electron microscope can all be used to observe the activities of the microorganisms such as flagella.
Protoplasts and Spheroplasts Bacteria ordinarily lyse in water or serum when the rigid cell wall peptidoglycan layer of the cell envelope is dissolved by lysozyme or other agents. Nonetheless, if stabilized by hypertonic solutions of sucrose or salts depending upon the organism, a wall-less, osmotically sensitive spherical body called a protoplast is liberated. If envelope components are retained the osmotically sensitive body is called a spheroplast. Gram-positive bacteria generally yield protoplasts, whereas gram-negative organisms yield spheroplasts since some outer membrane components inevitably are retained. Spheroplasts can also be produced by growth in hypertonic environments in the presence of cell wall synthesis inhibitors, such as penicillin. Spheroplasts and protoplasts actions are being viewed using microscopes.
Periplasm Periplasm, which occurs in the space between the plasma membrane and the outer membrane and can be seen using a binocular microscope, may readily be observed in gram negative bacteria but only with difficulty in gram-positive bacteria. This may be explained by the high internal osmotic pressures of gram-positive bacteria, which is 8 to 20 atm, compared to those of gram-negative bacteria, which is 3 to 5 atm. The periplasmic space of gram-negative bacteria varies with growth conditions and among individual bacteria. These growth conditions are studied with the help of a microscope. In E. coli, the periplasmic space has been shown by cytochemical staining to contain various proteins, including alkaline phosphatase, acid hexosephosphatase, and, cyclic phosphodiesterase. It is also thought to contain hydrolytic enzymes, such as acid phosphatase, and plasmid-controlled penicillinases, in addition to binding proteins that specifically bind sugars, amino acids, and inorganic ions. These can be released from the cell by osmotic shock such as rapid dilution of hypertonic cell suspensions, after EDTA treatment. Other enzymes, such as the chromosomally controlled penicillinases of E. coli, may be membrane associated, since they are released from the cell only during spheroplast formation. This strain of bacteria, which causes food poisoning is vividly observe with the use of a microscope.
The Plasma Membrane Beneath the rigid cell wall layer and in close association with it is the delicate cytoplasmic membrane, vitally important to the cell. In thin sections the plasma membrane shows a typical unit-membrane or trilaminar sandwich structure of dark-light-dark layers. The plasma membrane cannot be seen by the naked eye only. Teaching microscope during biology classes are being used in order for it to be clearly seen. Further, utilizing the tri-ocular microscope, the entire class or group of medical personnel is able to view the specimen because of its capability to project the specimen under study. The Membrane as an Osmotic Barrier Although bacteria, which are only perceived with the aide of the microscope, are regarded as extremely tolerant to osmotic changes in their external environment, they undergo either plasmolysis or plasmoptysis when placed in media of varying salt concentrations. Plasmolysis is the shrinkage of the membrane and cytoplasm from the cell wall, which resulted from placing cells in hypertonic solutions. Gram-negative cells are more easily plasmolyzed than are gram-positive cells, which correlate with their relative internal osmotic pressures. Plasmolysis actions and results are clearly viewed under a microscope.
The osmotic barrier in bacteria is indicated by their ability to concentrate certain amino acids against concentration gradients. In gram-positive bacteria, a gradient of 300 to 400 fold may exist across the surface layers. Phosphate esters, amino acids, and other solutes contribute to the internal osmotic pressure. Osmotic activity is also indicated by the cells selective permeability toward various compounds. The positivity and negativity of the bacteria using a gram stain are observed only with the use of a microscope. Various kinds of microscopes can be made use of. Membrane-associated Structures Membranes isolated after careful lysis account for some 30 percent or more of the cell weight. Up to 90 percent of the ribosomes may be isolated as a membrane-polyribosome-DNA aggregate.
Membrane Components Membranes contain 60 to 70 percent protein, 30 to 40 percent lipid, and small amounts of carbohydrate. The varied structures of these membranes are apparently viewed with the help of any microscopes. Phosphatidylethanolamines, which is 75 percent, phosphatidylglycerol, which is 20 percent, and the rest which are glycolipids are found as major constituents. Choline, sphingolipids, polyunsaturated fatty acids, and steroids are rare. Pathogenic mycoplasma integrates steroids from the environment into their plasma membranes. Glycolipids include diglycosvldiglycerides, found primarily in gram-positive bacterial membranes, which also contain lipoteichoic acids. A 55-carbon polyisoprenoid alcohol known as undecaprenol or bactoprenol occurs in small amounts.
Various enzymic activities are associated with membrane proteins. These include the energy-producing bacterial cytochrome and oxidative phosphorylation system, the membrane permeability systems, and various polymer-synthesizing systems. An ATPase has been isolated from knob-like membrane structures similar to those found in eucaryotic mitochondria. The latter are lucidly seen using the microscope.