Bacterial sheaths

Figure 8.6 High resolution transmission electron microscopy imagery reveals manganese and iron minerals that appear to be moving from the granular remnants of bacterial sheaths into adjacent clay minerals. The granular textures found between layered varnish consist of Mn-Fe precipitates on bacterial remains (Krinsley, 1998). Images are of varnishes from (A) Nasca, Peru (B, E) Death Valley (C, D) Kaho olawe, Hawaii (F) Antarctica. Scale bars in nanometres.

High resolution transmission electron microscopy imagery of manganese and iron minerals that appear to be moving from the granular remnants of bacterial sheaths into adjacent clay minerals. 

Polyneuritis is a disorder of the peripheral nerves. It involves damage to the myelin sheath. The condition is due to inflammation of the axonal membrane caused by viral or bacterial attack, i.e. an antoimmnne disease. Guillain-Barre syndrome is one form of polynenritis and is an example of an autoimmune disease caused by immune mimicry in response to a bacterial or viral antigen. It is discnssed in Chapter 17. 

Several other diseases exist which can destroy the myelin sheath. Many are a result of viral infections or the body s immune response to a bacterial infection. Guillain-Barre syndrome causes numbness and paralysis starting at the extremities radiating into the trunk of the body where it can cause complete respiratory collapse. Guillain-Barre has occurred in senior citizens who have been given flu vaccinations. The virus used in the vaccination may be attenuated (diminished in virility but not "killed") and still be capable of causing an infection. 

Other bacterial coats. Archaebacteria not only have unusual plasma membranes that contain phytanyl and diphytanyl groups (Section A,3)608 but also have special surface layers (S-Iayers) that may consist of many copies of a single protein that is anchored in the cell membrane.609 The surface protein of the hypothermic Staphylothermus marius consists of a complex structure formed from a tetramer of 92-kDa rods with an equal number of 85-kDa "arms."610 611 S-layers are often formed not only by archaebacteria but also by eubacteria of several types and with quite varied structures.612 14 While many bacteria carry adhesins on pili, in others these adhesive proteins are also components of surface layers.615 Additional sheaths, capsules, or slime layers, often composed of dextrans (Chapter 4) and other carbohydrates, surround some bacteria. 

Bacteriophage, a virus infecting bacterial cells, has a structure somewhat different from those previously described. A head contains the nucleic acid and the viral DNA passes through a tail during the infection process. In the T-even phages (Fig. 1), the tad consists of a tube surrounded by a sheath and is connected to a thin collar al the head end and a plate at the tip end. The sheath is capable of contraction and the plate possesses pins and tail fibers, which are the organs of attachment of the bacteriophage to the. wall of the host cell. 

The effectiveness of a disinfectant also depends upon the age of the microorganism. For example, young bacteria can easily be killed, while old bacteria are resistant. As the bacterium ages, a polysaccharide sheath is developed around the cell wall this contributes to the resistance against disinfectants. For example, when using 2.0 mg/L of applied chlorine dosage, for bacterial cultures of about 10 days old, it takes 30 min of contact time to produce the same reduction as for young cultures of about one day old dosed with one minute of contact time. In the extreme case are the bacterial spores they are, indeed, very resistant and many of the chemical disinfectants normally nsed have little or no effect on them. 

Fig. 1 Examples of bacterial hair styles , a Thick and straight type 1 fimbriated E. coli. Type 1 fimbriae are composite structures with a relatively rigid 8 nm wide rod tipped by a thin (2.5 nm) more flexible tip fibrillum. b Thin and wavy F17 fimbriated E. coli covered with 1-3 pm long, flexible, 2-3 nm wide fimbriae, c Tangled (capsules and sheaths) Y. pest is FI capsular antigen. No individual fibres are visible, but the capsule consists of a tangle of thin ( 2 nm) flexible fibres. AFM amplitude picture (a) kindly provided by Dr R. Willaert, Ultrastructure, VU Brussels TEM picture (b) kindly provided by I. Caplier, Protein Chemistry, VU Brussels and reprinted from [23] with permission from the publisher SEM picture (c) reprinted from [24] with permission from the publisher...

Tincture 1 5 with 50 percent alcohol. Note usnea is not easily soluble in alcohol unless it is mechanically ground first. The outer, green sheath will powder the inner cord will remain unpowdered and appear much like a ball of white hair. Both will give up their constituents to an alcohol/water combination). As a preventative or for immune stimulation 30 to 60 drops up to 4 times a day. For acute bacterial infections, including tuberculosis 1 teaspoon (5 ml) up to 6 times a day. 

Rice bacterial blight (Xanthomonas oryzae Dowson) Sheath blight of rice (Pellicularia sasakii (Shirai) S. Ito)... 

We have already considered one application of living system utilization in medicine, where genetically engineered anaerobic bacterial spores seek ont cancerous tissue (see Example 6.15.1). In another application, multiple sclerosis (MS) can be helped by transplanting cells from one part of the body to another (Thieme, 2001a). MS is the resnlt of the destruction of myelin sheaths around nerves in the brain and spinal cord. This slows the conduction of impulses greatly (see Section 4.4.3). Schwann cells taken from the limbs of patients and injected into MS-affected areas can produce new myelin and reverse the most devastating aspects of the disease. 

Coliphage attacks E. coli in a series of steps. First the long tail fibres come to rest on the surface of the cell, then the spiked base-plate is brought into contact with this surface. The lysozyme-like enzyme in the plate then depolymerizes a small area in the murein of the bacteria cell wall. The myosin-like sheath of the virus then contracts and the solid core pierces the bacterial membrane finally the viral DNA is injected into the cytoplasm (Lwoff, 1961). 

Anti-adhesive agents have been sought to prevent the sticking of the bacteria to teeth but generally these have not been successful, and bacteriocides are normally used. The problem is the mechanism of the bacterial adhesion, as shown in Fig. 12.25. It is thought that a fdm of polymer from saliva first attaches to the hydroxyapatite. Then bacteria attach to this coating. The bacteria produce a complex layer of cell sheath which glues the cells to each other. 

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