Bacterial cell capsules

Polysaccharides occur (1) in cell walls, (2) extracellularly in capsules and gums, and (3) inside of bacterial cells. The first two have already been discussed. 

Work at the EPA Gulf Breeze Laboratory has demonstrated the potential usefulness of encapsulation in the bioremediation of PAHs. A model system has been developed in which a pure culture capable of degrading fluoranthene (strain EPA505) has been successfully encapsulated in polyurethane foam and polyvinyl alcohol (Baker et al., 1988). The capsules can be stored for several months at 4 °C with only minimal loss of viability. Upon addition of the capsules to moist soil, fluoranthene mineralization commenced in approximately the same way as observed when fresh bacterial cells were added to the soil. These results are shown in Figure 5.7a. Since the same inoculation size was used in all flasks during this experiment, the results suggest that the immobilization process does not significantly affect microbial activity. 

Its chemical makeup is considered in Chapter 8. One of the layers is often referred to as the outer membrane. In some bacteria the wall may be as much as 80 nm thick and may be further surrounded by a thick capsule or glycocalyx (slime layer).13 The main function of the wall seems to be to prevent osmotic swelling and bursting of the bacterial cell when the surrounding medium is hypotonic. 

Uropathogenic E. coli cause 90% of the urinary tract infections. The bacteria colonize from the feces or perineal region and ascend the urinary tract to the bladder. With the aid of specific adhesins (pyelonephritis-associated pili) they are able to colonize the bladder. Another factor involved in the pathogenicity of the uropathogenic strains of E. coli is their resistance to complement-dependent bactericidal effect of serum. This phenomenon is associated with the presence of a capsule, which decrease the ability of antibodies and/or complement to bind to the bacterial surface, which in turn prevents the phagocytes from recognizing and engulfing the bacterial cells. 

The example describes the creation of a comparison between two entries uploaded into WebACT from the public DNA database. Each entry contains the DNA sequence and annotation for a gene cluster from S. pneumoniae encoding the biosynthesis of a particular polysaccharide capsule structure. Each strain of S. pneumoniae carries 1 version of the gene cluster out of a possible 90 (17). The different capsule types are conventionally determined by serotyping. The capsule forms the outer coating of these bacterial cells and differences in their structure affect interactions with the human host. 

D-Fructofuranosides occur abundantly in Nature. They occur in plants, examples include inulin, levan, and sucrose, and also in bacterial cell-walls and capsules such as those of species of Streptococcus, Haemophilus, and Yersinia 85 Unfortunately, synthesis of their glycosides presents the same type of problem as that in the synthesis of (3-mannosides, namely difficulty of approach of a nucleophile from the [3 side ... 

Capsules and capsular antigens are considered to be outer envelope polymers, usually high-molecular-weight acidic polysaccharides, which surround the bacterial cell in the form of a hydrophilic gel. Polysaccharides adhering weakly to the cell are known as slime layers. 

Biotechnological methods of hyaluronan production from bacterial strains involve cultivation in selected conditions where the polysaccharide capsule is formed during the stage of logarithmic growth on the surface of the bacterial cells. But at the stationary growing stage, HA can move into the cultural liquid and a capsule could become thin or disappears completely [30]. At the end of the process, up to 1-6 g of the desirable product could accumulate in 11 of the cultural liquid. HA accumulation could be controlled by the measurements of the viscosity of the cultural liquid. 

Unicellular bacteria and cyanobacteria consist of prokaryotic cells, which differ in several major respects from the eukaryotic cells of higher organisms. Illustrated in Figure 11.11, prokaryotic bacterial cells are enclosed in a cell wall, which in many bacteria is frequently surrounded by a slime layer (capsule). The thin cell membrane or cytoplasmic membrane on the inner surface of the cell wall encloses the cellular cytoplasm, controls the nature and quantity of materials transported into and out of the cell, and is susceptible to damage from some toxic substances. Hairlike pili... 

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