Cell wall bacterium

FIGURE 19.27 A DNA molecule is very large, even in bacteria. In this micrograph, a DNA molecule has spilled out through the damaged cell wall of a bacterium. 

The essential genetic material ofthe original vegetative bacterium is retained in the core or protoplast around this lies the thick cortex which contains the murein or peptidoglycan already encountered as a cell wall component (see Fig. 1.2). The outer coats which are protein in composition are distinguished by their high cysteine content. In this respect they resemble keratin, the protein of hair and horn. 

Although equal amounts of the two possible forms are generated in every synthesis of amino acids, (almost) only L-amino acids are incorporated into proteins and peptides. This phenomenon is valid for the amino acids in all life forms, from the bacterium to the elephant. But there are exceptions some antibiotics contain D-amino acids in their proteins, and these also occur in a few components of cell walls. Here, the D-amino acids have a certain protecting function with respect to degradation enzymes, which are specialised to deal with L-amino acids. 

Fowle et al. (2000) have measured the sorption by a soil bacterium (B. subtilis) of uranyl in 0.1 M NaC104 at 25°C as a function of pH, time, and solid solute ratio, using a batch technique. The stoichiometiy and thermodynamic stability of the important uranyl-surface complexes indicated that uranyl formed two different surface complexes, one involving neutral phosphate functional groups, and another with deprotonated carboxyl functional groups, on the bacterial cell wall ... 

Erwinia spp. are commonly present on vegetables at harvest. This bacterium has the characteristic of producing extracellular enzymes that degrade plant cell walls. Moreover, many Erwinia spp. such as E. carotovora are capable of using compounds as energy that are normally not utilized by most common bacteria (Jay 1992). Moreover, these species produce many enzymes (such as pectate lyase, polygacturonase,... 

It is a gram-negative, nonmotile bacterium. They are among the smallest of bacterial organisms and lack a true cell wall. This organism requires a host to survive. 

Plette, A. C. C., Benedetti, M. F. and van Riemsdijk, W. H. (1996). Competitive binding of protons, calcium, cadmium, and zinc to isolated cell walls of a grampositive soil bacterium, Environ. Sci. Technol., 30, 1902-1910. 

The Gram-positive bacterium Streptococcus pneumoniae is an important cause of respiratory tract infections, bacteremia, and meningitis. In this strain, the cell wall anchored pneumococcal surface protein A (PspA) has been demonstrated to bind lactoferrin [181]. PspA and closely related proteins in a variety of pneumococcal isolates are most likely involved in the sequestration of iron from lactoferrins, and finally contribute to the virulence of these bacteria. However, the means by which the pneumococcus acquires iron at the mucosal surface during invasive infection is not well understood at the molecular level [182],... 

Figure 1.3. Phagocytosis of Staphylococcus aureus by a human neutrophil. Neutrophils were incubated with opsonised S. aureus and fixed after 15 min incubation. The bacterium in the centre has been lysed, and only the cell wall remains. Source Experiment of Bernard Davies and John Humphreys, reproduced with permission from Colour Atlas of Paediatric Infectious Diseases, by Hart and Broadhead (Mosby Year Book Europe).

Mycobacterium is a genus of bacteria that has characteristic cell walls and unusual staining properties. AIDS patients are most commonly infected with an atypical form of tuberculosis bacterium called Mycobacterium avium inter-cellulare. This bacterium does not normally cause disease in healthy people, but in AIDS patients, it may cause tuberculosis-like disease in the lungs. The infection can also involve numerous other tissues, such as the bone marrow, and bacteria may be present in the blood at very high levels. Patients with this opportunistic infection will have fevers and low number of white blood cells. These infections are often resistant to drugs. 

In addition to transpeptidases, other penicillin-binding proteins (PBPs) function as transglycosylases and carboxypeptidases. All of the PBPs are involved with assembly, maintenance, or regulation of peptidoglycan cell wall synthesis. When (3-lactam antibiotics inactivate PBPs, the consequence to the bacterium is a structurally weakened cell wall, aberrant morphological form, cell lysis, and death. 

It is probable that the transport properties are relatively insignificant in the Ames assay, for the only possibility would be the transport of the agent through the cell wall of the bacterium. Thus it is probable that the dibenzylnitrosamine either does not undergo metabolism or, once the metabolism has occurred, the electrophile does not behave in the usual fashion to give a carcinogenic event. Some evidence has been reported which would... 

Figure 9.4 Mechanism of penicillin. By means of its highly reactive lactam ring, penicillin is able to deactivate the transpeptidase enzyme. This in turn leads to a halting of cell wall construction within the bacterium, ultimately leading to bacterial death.

Lysozyme is an enzyme that hydrolyzes some bacterial cell-walls, the bacterium used for the assay being Micrococcus lysodeikticus. Lysozyme is found in a wide variety of species and locations, including bacteriophages, blood, egg white, gastric secretions, milk, nasal mucus, papaya, sputum, and tears. The outstanding achievement in this field has been the elucidation of the crystal structures of some of the lysozyme-substrate complexes. 

By market volume the most important flavour molecule is L-glutamic acid. In 2004, the worldwide annual MSG production was estimated to be amount 1,500,0001 [21]. The amino acid is extensively used as taste enhancer, frequently in conjunction with nucleotides, a flavour impression which is also referred to as umamf, a term derived from the Japanese meaning deliciousness or a savoury or palatable taste. MSG is manufactured by aerobic cultivation of Coryne-bacterium glutamicum on starch hydrolysates or molasses media in large-scale bioreactors (up to 500 m ). Production strains with modified metabolic flux profiles and highly permeable cell walls for an improved product secretion are... 

Antibiotic resistance in bacteria is not a fixed property, and the degree of resistance detectable in the laboratory probably bears litde relationship to the resistance of the organism when growing in the intestinal tract of animals. The types of resistance that bacteria may develop to the action of antibiotics involve two distinct mechanisms mutation and inheritance. The former mechanism affects DNA sequence and results in the synthesis of a protein or macromolecule by the bacterial chromosome that differs from the original chemical entity, with the ability to interfere with the antibiotic activity. Because an antibiotic hinders a bacterium only after it has entered or crossed the cell wall and has bound to a target site, resistance can develop directly if the mutation has so altered the characteristics of the protein or macromolecule that the cell wall, receptor site, or transport mechanism is no longer friendly to the antibiotic. 

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